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NIST Special Publication 250-89 

NIST MEASUREMENT SERVICES: 

Spectral Irradiance Calibrations 

Howard W. Yoon and Charles E. Gibson 

Optical Technology Division 

Physical Measurement Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899-0001 

July 2011 

U.S. DEPARTMENT OF COMMERCE 

Gary F. Locke, Secretary 

National Institute of Standards and Technology 

Patrick D. Gallagher, Director 
National Institute of Standards and Technology Special Publication 250-89 

Nat. Inst. Stand. Technol. Spec. Publ. 250-89, 132 Pages, (July 2011) 

CODEN: NSPUE2 

NIST PRINTING AND DUPLICATION OFFICE 

GAITHERSBURG, MD: 2011
 

 iii

PREFACE 

The calibration and related measurement services of the National Institute of Standards 

and Technology are intended to assist the makers and users of precision measuring 

instruments in achieving the highest possible levels of accuracy, quality, and 

productivity. NIST offers over 300 different calibrations, special tests, and measurement 

assurance services. These services allow customers to directly link their measurement 

systems to measurement systems and standards maintained by NIST. These services are 

offered to the public and private organizations alike. They are described in NIST Special 

Publication (SP) 250, NIST Calibration Services Users Guide. 

The Users Guide is supplemented by a number of Special Publications (designated as the 

"SP250 Series") that provide detailed descriptions of the important features of specific 

NIST calibration services. These documents provide a description of the: (1) 

specifications for the services; (2) design philosophy and theory; (3) NIST measurement 

system; (4) NIST operational procedures; (5) assessment of the measurement uncertainty 

including random and systematic errors and an error budget; and (6) internal quality 

control procedures used by NIST. These documents will present more detail than can be 

given in NIST calibration reports, or than is generally allowed in articles in scientific 

journals. In the past, NIST has published such information in a variety of ways. This 

series will make this type of information more readily available to the user. 

This document, SP250-89 (2011), NIST Measurement Services: Spectral Irradiance 

Calibrations supersedes the NBS Special Publication 250-20 (1987). It describes the 

calibration of 1000 W tungsten quartz-halogen lamps over the wavelength region from 

250 nm to 2400 nm (test numbers 39030C-39046C in SP250, NIST Calibration Services 

Users Guide). Inquiries concerning the technical content of this document or the 

specifications for these services should be directed to the author or to one of the 

technical contacts cited in SP250. 

NIST welcomes suggestions on how publications such as this might be made more 

useful. Suggestions are also welcome concerning the need for new calibrations services, 

special tests, and measurement assurance programs. 

James K. Olthoff Katharine B. Gebbie 

Deputy Director for Measurement Services Director 

Physical Measurement Laboratory Physical Measurement Laboratory 
 

 iv

ABSTRACT 

This document describes the process of the realization, the maintenance and the 

dissemination of the spectral irradiance scale and its accompanying uncertainties at the 

National Institute of Standards and Technology. It describes the measurement procedures 

for the realization of the scale and the uncertainties of the detector-based spectral 

irradiance scale. During the realization process, the spectral irradiances are ultimately 

made Système International d'Unités (SI) traceable to the unit of electrical power through 

the electrical-substitution cryogenic radiometer and the unit of length through the 

aperture area and the distance measurements. This document also contains a 

representative calibration report and values for the NIST-disseminated spectral irradiance 

standards along with the irradiance calibration procedures manual. 

KEY WORDS: spectral irradiance scale, calibration, cryogenic radiometer, filter 

radiometer, high-temperature blackbody, uncertainties, temperature, 

Planck radiance 

 
 

 v

TABLE OF CONTENTS 

ABSTRACT ....................................................................................................................... iv

1. Introduction .....................................................................................................................1

1.1 Spectral Irradiance ....................................................................................................2

1.2 History of the NIST spectral irradiance scales .........................................................2

1.3 Description of current services in spectral irradiance calibrations ...........................3

2. Scale Realization .............................................................................................................4

2.1 Measurement equation for temperature determination ............................................5

2.2 Description of the high-temperature blackbody (HTBB) .........................................6

2.3 Validation of the HTBB as a Planckian Radiator .....................................................6

2.4 HTBB Operation ......................................................................................................8

2.5 Spectral Irradiance Transfer to 1000 W FEL Lamps ...............................................9

3.  Description of the FASCAL 2 Facility .........................................................................11

3.1 Spectroradiometer system ......................................................................................12

3.2 Performance Characterizations of the FASCAL 2 Facility ....................................14

4. Uncertainty Analysis of the Spectral Irradiances Issued on FEL Lamps .....................18

4.1 Uncertainties of the HTBB detector-based temperatures .......................................18

4.2 Uncertainties of the spectral irradiance realization to primary working standards 18

4.3 Uncertainties of the issued spectral irradiance standards .......................................19

4.4 International comparisons to support the NIST assigned uncertainties .................20

5. Future Work ..................................................................................................................23

Acknowledgments..............................................................................................................23

References ..........................................................................................................................24

Appendix A: Lamp selection process........................................................... A1 

Appendix B: Orientation dependence of the FEL lamp....................................... B1 

Appendix C: Physical alignment of the FEL lamp............................................ C1 

Appendix D: Atmospheric absorption and FEL interpolations.............................. D1 

Appendix E: Sample calibration report......................................................... E1 

Appendix F: Irradiance calibration procedures manual....................................... F1 

Appendix G: Radiation constants................................................................ G1 

Appendix H: Conversion factors................................................................ H1 

Appendix I: Alignment jig........................................................................ I1 

Appendix J: Kinematic lamp socket............................................................. J1 

Appendix K: Calibration data points............................................................ K1 

Appendix L: Calibration services................................................................ L1 
 

 vi

LIST OF FIGURES 

Figure 1. The primary scale realization for the NIST spectral irradiance scale. The 

cryogenic radiometer calibrates the trap detectors for optical power by 

substitution with electrical power. The aperture areas and distances are 

traceable to length standards. ............................................................................ 4

Figure 2. The irradiance responsivities of the filter radiometers used in the realization as 

measured with the NIST detector-based scale realized from the electrical 

substitution cryogenic radiometer. The Planck radiance law at 3000 K is 

shown plotted on the right axis. ........................................................................ 5

Figure 3. The comparison of spectral radiances found using the radiances determined 

from the VTBB with the radiances found using the detector-based filter 

radiometers for the measurements on indicated dates. The agreement within 

the expanded uncertainties of the comparisons indicates that the emissivity of 

the HTBB as well as the temperature assignment are within the combined 

uncertainties of the comparison. ....................................................................... 8

Figure 4. The time-dependent drift of the HTBB. The HTBB was monitored with 

optical feedback from the rear. Measurements are performed during a time 

duration of about 30 min. The drift of the HTBB accounted by a component 

in the total uncertainty budget. .......................................................................... 9

Figure 5. The spectral irradiance of the HTBB at 2950 K with the measurement 

parameters as described with the spectral irradiances of a typical 1000 W FEL 

lamp. The measurement parameters for the HTBB were chosen to closely 

match the spectral irradiance of the lamp. ...................................................... 11

Figure 6. The optical layout showing the monochromator table with the positions of the 

input and the exit optics. A double monochromator in a Czerny-Turner design 

is used for dispersion and stray-light rejection. .............................................. 13

Figure 7. The left axis denotes the percent differences from the mean of the spectral 

irradiances measured over a duration of 1 h. A total of three consecutive 

measurements were performed with the individual measurements denoted by 

squares, triangles, and circles. The right axis indicates the typical spectral 

irradiance of a 1000 W FEL lamp. The spectral irradiances were measured 

using the PMT (open), the Si diode (solid), and the InGaAs diode (opencrossed). .......................................................................................................... 15

Figure 8. The residuals of the linear fit to the wavelength calibrations performed using 

various low-pressure lamp sources for the wavelength region from 200 nm to 

1000 nm. ......................................................................................................... 16

Figure 9. The residuals of the linear wavelength fit to the wavelength calibrated using 

various spectral line sources for the near IR wavelength region. ................... 17

Figure 10. The expanded uncertainties of the PWS and the total uncertainties of the 

issued spectral irradiance standards with respect to SI units. ......................... 19

Figure 11. The percent differences from the mean of three separate, independent spectral 

irradiance scale realizations performed on four separate days. The differences 

are shown with the assigned expanded uncertainties of the working standards 

for the detector-based spectral irradiance scale. ............................................. 20
 

 vii

LIST OF TABLES 

Table 1. The current spectral irradiance calibration tests offered. ................................... 3

Table 2. The specifications of the monochromator system and the detectors used to 

measure the spectral irradiances. ...................................................................... 13

Table 3. The order-sorting filters used in FASCAL 2 with the 6-position filter wheel 

placed at the entrance to the monochromator. .................................................. 14

Table 4. Uncertainty components for the HTBB temperature determination. At the 

HTBB temperature of 2950 K, an irradiance response uncertainty of 0.26 % 

corresponds to a temperature uncertainty of 0.86 K (k = 2). ............................ 21

Table 5. Uncertainty budget for spectral irradiance calibrations using FASCAL 2.... . 22 
 

 1

1. Introduction 

This document supersedes the NBS Special Publication 250-20 (1987). In 2000, a 

new detector-based spectral irradiance scale was realized using a high-temperature 

blackbody in conjunction with absolute filter radiometers, traceable to the absolute 

cryogenic radiometer. The filter radiometers are used to determine the thermodynamic 

temperature of the blackbody. This new scale reduced the uncertainties in the 

disseminated spectral irradiances as compared to the gold fixed-point blackbody derived 

scale of 1990 and 1992. Beginning with the calendar year 2001, all NIST-disseminated 

spectral irradiance standards have been based upon the detector-based scale. 

The development and the use of cryogenic radiometers have led the trend toward 

decreasing uncertainties in the radiometric and the photometric scales due to 

improvements in the absolute power measurements [T1T, T2T]. Furthermore, detector-based 

scales can be often maintained with shorter measurement chains and lower uncertainties 

than source-based scales. For example, the photometric scale at NIST has been detectorbased and traceable to the NIST High-Accuracy Cryogenic Radiometer (HACR) since 

1993 [T3T], and the implementation of the detector-based photometric scale resulted in a 

factor of two reduction in the expanded uncertainties compared to the previous, sourcebased photometric scale [T4T]. The establishment of the detector-based spectral irradiance 

scale is a part of a long-term effort in the Optical Technology Division aimed at reducing 

the realization chain and lowering the uncertainties in the issued standards. 

This document describes the process of the realization, the maintenance and the 

dissemination of the spectral irradiance scale at the National Institute of Standards and 

Technology and its accompanying uncertainties. It describes the measurement 

procedures for the realization of the scale and the uncertainties of the detector-based 

spectral irradiance scale. During the realization process, the spectral irradiances are 

ultimately made Système International d'Unités (SI) [T5T] traceable to the units of electrical 

power through the electrical substitution cryogenic radiometer and the unit of length and 

the aperture area through the distance measurements. The uncertainties described in this 

document have been analyzed according to the ISO Guide to the Expression of 

Uncertainty in Measurement [T6T]. The appendix contains a representative calibration 

report and values for the NIST-disseminated spectral irradiance standards. It also 

describes the proper handling and alignment of the standards to minimize the transfer 

uncertainties. The process of lamp selection prior to calibrations is described, and the 

prior knowledge about the long-term stability of the lamps results in minimization of 

redundant measurements [T7T]. 

 
 

 2

 1.1 Spectral Irradiance 

Spectral irradiance is the measure of the optical power, Φ, incident on an area, dA, per 

unit wavelength, dλ, and is denoted by 

λ λ dA d

d E ⋅Φ =

2

. (1) 

A commonly used unit to denote spectral irradiance is microwatts per square centimeter 

area per nanometer wavelength or μW cmP

-2P

 nmP

-1P

. 

The spectral irradiance source standards calibrated at NIST are used in turn to 

calibrate spectroradiometers which measure the spectral power incident on an area at a 

set distance from the source. For example, the NIST issued spectral irradiance standards 

are used to determine the solar terrestrial spectral irradiance, especially in the ultraviolet 

wavelength region, to provide data on climate change and health of ecosystems [T8T]. 

These standards are also used to determine the spectral irradiances of various sources 

such as lamps and light emitting diodes, and also to determine the color temperature of 

sources [T9T]. Photometric source scales such as the lumen can be also be derived from 

spectral irradiance sources. The spectral irradiance sources could also be used in 

conjunction with spectral reflectance standards to generate spectral radiance [T10T]. Many 

national measurement institutes also use NIST spectral irradiance standards as the basis 

in generating their own national spectroradiometric and photometric scales. 

1.2 History of the NIST spectral irradiance scales 

Due to the central role of spectral irradiance source standards in many radiometric 

and photometric calibrations, NIST has long provided these standards. The earliest 

NIST-calibrated sources were total irradiance standards issued in 1913 by Coblentz who 

calibrated them by comparison to blackbodies [T11T]. Much later in 1963, the first spectral 

irradiance standards were issued using a 200 W quartz-iodine lamp with a coiled-coil 

tungsten filament [T12T]. It was soon recognized that a source with greater radiation was 

needed to calibrate sources such as the sun, and in 1967, 1000 W lamps were first issued 

[T13T]. Due to the difficulties in scaling up the irradiances to the level of the 1000 W 

lamps, the realization of the scales to Système International d'Unités (SI) was performed 

infrequently. A new scale was realized 1973 [T14T], and the first Consultative Committee 

on Photometry and Radiometry (CCPR) comparison performed in 1976 [T15T]. The next 

CCPR comparison was piloted by NIST in 1990 coincident with a new realization of the 

scale [T16T]. In recognition of the difficulties in realizing a scale from the gold-point 

blackbody near 1337 K to calibrate a source with distribution temperature of 3200 K, 

work was performed to realize the scale using a high-temperature blackbody with 

detector-based thermodynamic temperature in 2000 [T17T]. The NIST detector-based 

spectral irradiance was used in the CCPR K1-a key comparison [T18T] of spectral 

irradiance from 250 nm to 2500 nm, and the detector-based spectral irradiance scale was 

realized again in 2003. A new facility, the Facility for Automated Spectroradiometric 

Calibrations 2 (FASCAL 2), was developed in 2001 to reduce the transfer and realization 

uncertainties and to meet the increased demand for these standards. This document 

describes the process of realization of the NIST spectral irradiance scale from the SI units 

and the procedure for the derivation of the spectral irradiance from those units. 
 

 3

1.3 Description of current services in spectral irradiance calibrations 

The current calibration services according to the test numbers and the descriptions of 

the tests are listed in Table 1. The tests are grouped according to the needs of the users 

such as the ultraviolet community for measurements from 250 nm to 450 nm, the 

photometric community for the wavelength region from 350 nm to 800 nm, and the 

selected short-wave infrared region along with the full wavelength region from 250 nm to 

1600 nm or from 250 nm to 2400 nm. Since many NIST customers also have longstanding history of usage of the same lamp, recalibrations are grouped differently from 

the issuing of newly calibrated lamps. Such breakdowns of the calibrations into 

categories are in response to customers request for reducing calibration costs and turnaround times for the calibrations. 

Table 1. The current spectral irradiance calibration tests offered. 

Test Number Description 

39030C Spectral Irradiance Standard, 1000 W Tungsten Quartz–Halogen 

Lamp (250 nm to 450 nm) 

39031C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(250 nm to 450 nm) 

39032C Spectral Irradiance Standard, 1000 W Tungsten Quartz–Halogen 

Lamp (350 nm to 800 nm) 

39033C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(350 nm to 800 nm) 

39040C Spectral Irradiance Standard, 1000 W Tungsten Quartz–Halogen 

Lamp (250 nm to 1600 nm) 

39041C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(250 nm to 1600 nm) 

39045C Spectral Irradiance Standard, 1000 W Tungsten Quartz–Halogen 

Lamp (250 nm to 2400 nm) 

39046C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(250 nm to 2400 nm) 

 
 

 4

2. Scale Realization 

At the National Institute of Standards and Technology, the spectral irradiance 

scale is realized using a detector-based scale. The NIST spectral irradiance scale is 

realized using filter radiometers (FR) calibrated for absolute, spectral power responsivity 

traceable to the NIST cryogenic radiometer. The cryogenic radiometer measures the 

optical power by the substitution of electrical power for comparison [T19T]. Thus the 

measured optical power is traceable to electrical power. The aperture areas which are 

needed for conversion of radiant power to irradiance are measured using interferometric 

techniques [T20T]. The calibrated FRs are then used to determine the radiance temperature 

of a high-temperature blackbody (HTBB) operating near 3000 K. The spectral irradiance 

of the HTBB is determined using the knowledge of the geometric factors and Planck 

radiance law and then is used to assign the spectral irradiances of a group of 1000 W FEL 

lamps. Thus the NIST spectral irradiance scale is ultimately traceable to the electrical 

power and the unit of length. The procedure for the realization is shown in Fig. 1. 

Cryogenic 

Radiometer 

Trap Detectors 

Silicon Working 

Standard Detectors 

Filter Radiometers 

High-temperature 

Blackbody 

Primary Working 

Standard Lamps 

Aperture Areas 

FR-HTBB 

distance 

Figure 1. The primary scale realization for the NIST spectral irradiance scale. The cryogenic radiometer 

calibrates the trap detectors for optical power by substitution with electrical power. The aperture areas and 

distances are traceable to length standards. 

 
 

 5

2.1 Measurement equation for temperature determination 

The radiance temperature of the high-temperature blackbody is found using a 

measurement equation, which describes the optical flux transfer with circular and coaxial 

source and receiver apertures [T21T]. For a filter radiometer, the signal S is given by, 

ε () ( ) λ λ λ π π δ R L T d

D

G r r S , 2 (1 ) 2 2

BB ∫ + = , (2) 

where ε is the emissivity, R is absolute spectral power responsivity. The geometric 

factors D and δ, are given by D P

2

P

 = d P

2

P

 + r P

2

P

 + rB

BBPB

2

P

 and δ = r P

2

P

rB

BBPB

2

P

/D P

4

P

, where rB

BBB and r 

are the radii of the blackbody aperture and the filter radiometer apertures, respectively, 

and d is distance between the filter radiometer aperture and the blackbody aperture. G is

the preamplifier gain, and L is the spectral radiance found using the Planck radiation law. 

The spectral power responsivity of the filter radiometers are measured in the NIST 

Spectral Comparator Facility TP

22PT. The radiance temperatures are found by iteratively 

changing the blackbody temperature in Eq. 2 until an exact match of the calculated signal 

to the measured signal is found. The irradiance responsivities of the FRs used for the 

realization are shown in Fig. 2 along with the Planck radiance at 3000 K. 

200 400 600 800 1000 10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

 Wavelength [ nm ]

Irradiance Responsivity [ A cm2 / W ]

 FR2

 FR3

 FR4

 Spectral Radiance [ 

μW/ cm2 nm sr ]

Figure 2. The irradiance responsivities of the filter radiometers used in the realization as measured with 

the NIST detector-based scale realized from the electrical substitution cryogenic radiometer. The Planck 

radiance law at 3000 K is shown plotted on the right axis. 

The uncertainties of the radiance temperatures found using the filter radiometers 

are primarily determined by the uncertainties in the spectral power responsivity. The 

lowest uncertainties are maintained in the visible wavelength region from 400 nm to 900 
 

 6

nm where the spectral power responsivity of the Si-trap transfer detector can be smoothly 

interpolated between the discrete laser calibration wavelengths of the cryogenic 

radiometer. The uncertainties of the spectral power responsivity can be directly 

converted to uncertainties in temperature using the derivative of the Wien approximation 

with respect to temperature, 

2

2

T

c T

L

L Δ = Δ

λ , (3) 

where the relationship between the uncertainty in radiance, L, to the uncertainty in 

blackbody temperature, T, and cB

2 Bis the second Planck’s constant, 1.4387752 cm K, and λ

is the wavelength. The Wien approximation is used to simplify the handling of 

equations. Under these experimental conditions, no appreciable differences exist 

between Eq. 3 and the similar differential equation found using the Planck’s radiance law 

in the wavelength between 250 nm and 2400 nm. Due to the changes in the shape of the 

blackbody radiance with temperature as described in the Planck radiance law, the 

temperature uncertainties are both dependent on temperature as well as wavelength. 

2.2 Description of the high-temperature blackbody (HTBB) 

One of the technological advances which makes possible the realization of the 

detector-based spectral irradiance scale is the development of pyrolytic-graphite 

blackbodies, enabling extended operations near 3000 K without rapid degradation of the 

cavity [T23T]. The high-temperature blackbody used in this work consists of pyrolyticgraphite rings with an inner diameter of 24 mm stacked to form a cavity with a depth of 

14.5 cm. The cavity bottom consists of an inverted cone with an apex angle of about 

150°, and the radiance at the backside of the cavity bottom is imaged through an opening 

at the rear of the cavity using a fused-silica lens onto a temperature-stabilized photometer 

for operation in closed-loop configuration. The lens also serves to seal the rear of the 

blackbody cavity to atmosphere. The current of the HTBB power supply is adjusted 

using a control loop to maintain a constant output from the photometer. Although the 

spectral irradiance in the ultraviolet wavelength region could be increased with higher 

temperatures, the HTBB was operated at near 2950 K to avoid possible changes in the 

spectral emissivity of the blackbody due to the sublimation of the graphite [T24T]. Since 

the graphite rings expand about 10 % from room temperature to near 3000 K, the current 

was increased at 0.1 A/s to nearly 510 A at 2950 K to allow gradual expansion of the 

cavity. The HTBB was also turned off in a similar manner to avoid thermo-physical 

shocks. 

2.3 Validation of the HTBB as a Planckian Radiator 

To determine the spectral emissivity of the HTBB, the spectral radiance of the 

HTBB was measured from 250 nm to 2400 nm at discrete wavelengths by comparison to 

a variable-temperature blackbody (VTBB) with a high emissivity. The VTBB is a 

NIST-designed blackbody with an internal diameter of 11 mm with an opening of 2 mm 

diameter to result in an estimated emissivity > 0.999 [T25T]. The Any temperature nonuniformity of the cavity would lead to deviations of the HTBB spectral radiance from a 

single-temperature Planck radiance. For these comparisons, the temperature of the 
 

 7

VTBB was set at 2687 K and the temperature of the HTBB was set at 2950 K. Although 

the temperatures are different, the radiance ratios did not differ even at 250 nm, where the 

differences are greatest, by more than a factor of seven. Furthermore, prior to these 

measurements, the linearity of the spectroradiometer has been measured at various 

wavelengths using the portable Beamconjoiner [T26T] and found to be linear under these 

experimental conditions. The spectral radiance determinations were performed before 

and after spectral irradiance transfer to a set of 1000 W FEL lamps. The checks of the 

HTBB as a Planckian radiator were performed to verify that the HTBB did not change in 

the spectral distribution since the FR’s are used to measure over a relatively broad 

spectral region. 

The spectral radiance measurements of the HTBB were performed with the 

aperture in front of the spherical input mirror to the spectroradiometer reduced to 4 cm 

diameter resulting in F/25 focused at the opening of the HTBB at the plane of the watercooled aperture. The reduction in the opening of the spherical input mirror resulted in a 

circular target of 12 mm diameter at the bottom of the HTBB cavity. To keep the same 

target area constant for the measurements, in both the spectral irradiance and the spectral 

radiance modes the HTBB was mounted on a motorized translation stage for control of 

the distance between the HTBB and the measuring instruments. If possible, the same 

area at the rear of the HTBB should be viewed for all measurements to avoid errors from 

the possible spatial non-uniformity of the HTBB. 

The temperature of the variable-temperature blackbody was determined using 

spectral radiance ratios at 655 nm to a vacuum tungsten-filament lamp maintained at the 

freezing-temperature of gold as prescribed in the ITS-90. The spectral radiance of the 

HTBB was determined at discrete wavelengths by comparison to the VTBB and also 

determined from the radiance temperature found using the filter radiometers. The 

radiance temperatures of the HTBB found using the filter radiometers were in agreement 

with those found using the ITS-90 ratios to within 0.5 K at all instances such comparisons 

were performed. The respective blackbodies were compared using spectral radiance 

ratios, 

λ,VTBB

λ,HTBB

λ,HTBB λ,VTBB λ S

S

L = L f . (4) 

The LB

λB and the SBλB denote the spectral radiance and the measured spectral radiance 

response of the HTBB and the VTBB, and λ f is the possible linearity correction to the 

response ratios. The spectral radiances of the HTBB were found to conform to a single 

temperature Planck radiance law to within the combined uncertainties of the 

measurements as shown in Fig. 3. Figure 3 shows the percent differences from a single 

temperature Planck radiance law with the temperature of the HTBB determined using the 

FR’s and the spectral radiances determined using the VTBB. The errors bars on the 

individual comparisons correspond to the expanded uncertainty of 0.86 K at 2943.4 K 

converted to a spectral radiance uncertainty using the derivative of the Wien 

approximation from Eq. 2. As expected for comparison of two blackbodies, the 

differences in the spectral radiance becomes smaller with increasing wavelength, but 

there are no discernible increasing spectral differences toward the shorter wavelengths, as 

would be expected if either of the temperature assignments of the respective blackbodies 

were in error. The differences between the detector-based radiance temperatures and the 
 

 8

source-based determinations also agree with the previous measurements, which also 

showed differences of < 0.5 % from 250 nm to 1000 nm [T27T]. 

The spectral radiances from the VTBB are determined using Planck radiance law 

from the assigned radiance temperatures at 655.3 nm and the estimated VTBB emissivity 

[T28T]. The emissivity is estimated using calculations from the partial reflectivity and the 

solid angle opening of the VTBB and experimental determinations with changing the 

solid angle of the opening. The spectral radiances of the HTBB are in turn assigned 

using the VTBB from the respective signals, i, and the gains, G, 

VTBB

VTBB VTBB

HTBB HTBB

HTBB, VTBB

L

G i

G i L ⋅

⋅ = . (5) 

0 500 1000 1500 2000 2500

-1.0

-0.5

0.0

0.5

1.0

 100 * [L HTBB, FR - L HTBB, VTBB ] / L HTBB, VTBB 

Wavelength [ nm ]

 09/21/00

 09/27/00

 10/06/00

 10/19/00

Figure 3. The comparison of spectral radiances found using the radiances determined from the VTBB with 

the radiances found using the detector-based filter radiometers for the measurements on indicated dates. 

The agreement within the expanded uncertainties of the comparisons indicates that the emissivity of the 

HTBB as well as the temperature assignment are within the combined uncertainties of the comparison. 

2.4 HTBB Operation 

The measurements of the HTBB temperatures are performed with the filter 

radiometers placed on a motorized table for individual alignment along the optical axis of 

the HTBB. A water-cooled precision aperture is placed in front of the HTBB, and the 

distance from this aperture to the filter radiometer aperture is measured using a 

micrometer. The current to the HTBB is controlled by a servo loop, and an optical 

detector monitors the rear of the cavity. The radiance temperature measurements over a 

time period of 4 h are plotted in Fig. 4. A determination of the spectral radiance of the 
 

 9

HTBB can be performed in about 30 min, and the temperature of the HTBB is stable 

during these measurements. For clarity only the temperatures measured using FR4 are 

plotted with the 0.21 K (k = 2) uncertainties. The temperature determinations using the 

three FRs are in agreement within their combined uncertainties. 

09:00 10:00 11:00 12:00 13:00 14:00 15:00

2952.0

2952.5

2953.0

2953.5

2954.0

 Temperature [ K ]

 Time [ h ]

 FR2

 FR3

 FR4

Figure 4. The time-dependent drift of the HTBB. The HTBB was monitored with optical feedback from 

the rear. Measurements are performed during a time duration of about 30 min. The drift of the HTBB 

accounted by a component in the total uncertainty budget. 

2.5 Spectral Irradiance Transfer to 1000 W FEL Lamps 

The spectral irradiance assignment of twelve 1000 W FEL working standard lamps 

occurred over a two week period from September 28 to October 12, 2000. The spectral 

irradiances of a group of three lamps were assigned at one time, and the measurements 

were separated into the ultraviolet and the visible wavelength region, 250 nm to 900 nm, 

and the short-wave infrared region, 800 nm to 2400 nm. Since there are four separate 

FEL lamp measurement stations, each of the measurements of individual lamp was 

performed in a different station using different shunt resistors, power supplies, and lamp 

mounts. Each of the lamp stations were checked for possible position effects, and no 

perceptible effects due to station-to-station variations were found. 

The HTBB was turned on at least 2 h before use, and temperature-stabilized using 

the optical feedback. The temperature of the HTBB was assigned using the FR’s and the 

spectral irradiance responsivity of the spectroradiometer assigned using the known 

spectral irradiance of the HTBB. All the spectral irradiance responsivity transfers to the 

spectroradiometer were done at a distance of 43.406 cm (±0.005 cm) from the HTBB 

aperture to the 1 cmP

2

P

 area aperture of the integrating sphere receiver (ISR) resulting in a 

24.7 mm diameter circular target area at the cavity bottom. The spectral irradiance 
 

 10

responsivity of the spectroradiometer is assigned using the known spectral irradiance of 

the HTBB at the input aperture of the ISR, 

( )

2

2

BB ,

, 

D

L T r E HTBBλ π

λ = , (6) 

with the measurement parameters as defined in Eq. 2. 

After the spectral irradiance responsivity assignment of the spectroradiometer, the 

spectral irradiance of a group of three FEL lamps were assigned with each lamp 

measured in three separate source positions. The spectral irradiance of each lamp was 

assigned using, 

HTBB

FEL

FEL HTBB S

S

E E f

,

,

, ,

λ

λ

λ = λ λ , (7) 

where EB

λ, FEL (HTBB)B is the spectral irradiance of the FEL lamp (HTBB), SBλ, FEL (HTBB)B is the 

net signal from the FEL lamp (HTBB) measured using the spectroradiometer, and fB

λB is 

the linearity correction factor for the comparison. With the use of a shutter, the 

background signals were subtracted from the total signals to obtain the net signals. The 

distance of the HTBB from the ISR was also chosen such that the same gain factors could 

be used to measure both the FEL and the HTBB. Figure 5 is a plot of the calculated 

spectral irradiances of the HTBB at 2950 K plotted with the spectral irradiances of a 

typical 1000 W FEL lamp with the blackbody source aperture of 9.9933 mm (± 0.0002 

mm) diameter and the ISR receiving aperture of 11.2838 mm (± 0.0002 mm) in diameter 

separated by a distance of 43.406 cm (±0.005 cm). At all wavelengths, Fig. 5 shows that 

the HTBB has a greater spectral irradiance than the FEL lamp. Although the spectral 

irradiance changes by a factor > 10P

3

P

 from 250 nm to 2400 nm, the HTBB/FEL signal 

ratio does not exceed 2.5. The close match of the irradiances was chosen to minimize 

possible errors resulting from signal-to-noise, non-linearity, and stray-light effects. 
 

 11

0 500 1000 1500 2000 2500 3000

10-2

10-1

100

101

102

 Wavelength [ nm ]

 Spectral Irradiance [ 

μW / cm2/ nm ]

 HTBB 2950 K

 1000 W FEL

Figure 5. The spectral irradiance of the HTBB at 2950 K with the measurement parameters as described 

with the spectral irradiances of a typical 1000 W FEL lamp. The measurement parameters for the HTBB 

were chosen to closely match the spectral irradiance of the lamp. 

3. Description of the FASCAL 2 Facility 

Figure 6 shows the physical layout of the FASCAL 2 facility. The sources and 

the rails for moving the spectroradiometer system are placed on a single 4.23 m by 1.52 

m fixed optical table, and the spectroradiometer is placed on a smaller, 1.52 m by 0.91 m 

moveable optical breadboard for translation between the separate sources. The optical 

breadboard is placed on linear rails, and the movement is controlled by a ball screw 

driven by a DC servo motor with feedback control. The total range of movement is 3.5 

m, and the linear position of the spectroradiometer table is measured using a 4 m long, 

linear encoder; the linear position of the spectroradiometer is reproducible to 2.5 μm. 

The facility has four separate lamp mounts to calibrate the NIST disseminated spectral 

irradiance sources, FEL lamps, which are placed in kinematic lamp mounts with 6-axes 

of adjustments for alignment. The electrical power to the lamps is controlled using a 

calibrated shunt resistor with a temperature coefficient of resistance of 3 ppm / C°, and 

the lamp current is actively controlled using 16 bit current regulation. The lamp voltages 

are also recorded. The last station holds the high-temperature blackbody (HTBB) 

capable of extended operations near 3000 K. The temperature of the HTBB is detectorbased and assigned using filter radiometers calibrated for absolute spectral irradiance 

responsivity for the realization of the spectral irradiance scale. 

 
 

 12

3.1 Spectroradiometer system 

 The spectroradiometer system is also shown in detail in Fig. 6. The spectral 

irradiances of the sources are measured using an integrating sphere receiver (ISR) with a 

circular opening with 1 cmP

2

P

 aperture area. The ISR is a 2.54 cm diameter packed 

polytetrafluoroethylene (PTFE) sphere for high transmittance throughout the spectral 

range of measurements. A 2 mm by 10 mm opening is made at the side of the ISR and 

imaged 1:1 using a 30.48 cm focal length spherical mirror. A flat folding mirror is used 

to couple the light into the monochromator. An additive-dispersive double 

monochromator (McPherson 2035DTP

*

PT) with dual gratings placed in motorized grating 

turrets is used, and a combination of 5 different filters are used for second-order rejection 

from the grating and for further stray-light rejection. The entrance and the exit slits of the 

monochromator are 2 mm wide and 10 mm high and unchanged during the course of the 

measurements. The width of the intermediate slit is opened to 4 mm with the height kept 

the same as the entrance and exit slits. The monochromator is a Czerny-Turner design 

with a focal length of 0.35 m and an effective aperture of F/4.8. The angular change of 

the grating is achieved using a sine-bar mechanism and driven with a DC servo motor 

with an absolute encoder with 2P

14P

 or 16,384 pulses per revolution attached to the shaft of 

the sine-bar mechanism for wavelength measurements. The temperatures of the 

monochromators are also monitored using platinum resistance thermometers, and 

recorded during the spectral irradiance measurements. To avoid errors in the wavelength 

arising from thermal changes in the monochromator, the monochromator section is 

temperature stabilized using forced air from TE coolers set to the ambient temperature of 

the laboratory prior to turning on the FEL lamps. To avoid stray light, the entire 

monochromator system including the input optics and the detectors are covered using a 

light-tight box. 

HTBB

Lamp Stations

Moving 

Spectroradiometer

Platform

InGaAs

Si

PMT

ISR
 

 13

Figure 6. The optical layout showing the monochromator table with the positions of the input and the exit 

optics. A double monochromator in a Czerny-Turner design is used for dispersion and stray-light rejection. 

Three separate detectors with two gratings and spectral selection filters are used 

for spectral coverage from 200 nm to 2500 nm. The spectral range of the gratings and the 

detectors are shown in Table 1, and although the blaze wavelength is outside the range of 

the Si diode wavelength region, the throughput of the monochromator is adequate. For 

measurements in the ultraviolet wavelength region, a Hamamatsu R106 low-noise bialkali side-on photomultiplier tube (PMT) is used. The bi-alkali PMT is chosen for low 

Table 2. The specifications of the monochromator system and the detectors used to 

measure the spectral irradiances. 

Beginning 

Wavelength 

[ nm ] 

End 

Wavelength 

[ nm ] 

Grating 

[g/mm] 

Grating 

Blaze 

[ nm ] 

Dispersion 

[ nm/mm ] 

Bandwidth 

[ nm ] 

Type of 

Detector 

Mode of 

Operation 

200 nm 450 nm 1200 300 2 4 Bi-alkali 

PMT DC 

350 nm 1100 nm 1200 300 2 4 TE-cooled 

Si diode DC 

900 nm 2500 nm 600 1250 4 8 

TE-cooled 

ExtendedInGaAs 

diode 

AC 

 

 

temporal drift and low dark currents. The temperature of the PMT is stabilized to - 26 °C 

using a temperature-feedback controller, and the PMT is attached to the output port of the 

monochromator. A fused silica lens is attached to the PMT housing and focuses the 

image of the output slit onto the PMT with 2:1 de-magnification factor. Detectors are 

selected by the use of a motorized 45° mirror, internal to the monochromator. The 2.4 

mm by 2.4 mm square silicon (Si) photodiode is temperature stabilized and cooled to - 

25 °C for low-noise operation. The 2 mm diameter indium gallium arsenide (InGaAs) 

photodiode is cooled to - 80° C using 4-stage TE coolers, and the InGaAs diode is 

selected for extended responsivity to 2500 nm. For the extended wavelength of 

measurements, order-sorting filters are critical to reduce the second-order radiation 

generated by the gratings when measuring a broad-band source. Table 3 lists the ordersorting filters used with the filter types and the specifications along with the operational 

wavelengths listed. For the ultraviolet wavelength region from 250 nm to 400 nm, ordersorting filters are not used. 

 
 

 14

Table 3. The order-sorting filters used in FASCAL 2 with the 6-position filter wheel 

placed at the entrance to the monochromator. 

 Filter Specification [nm ] Operation Wavelengths [nm ]

Filter wheel position Filter Type Beginning (t=0.7) End (t=0.7) Begin End 

1 BG-24 250 425 250 400 

2 BG-40 370 570 450 550 

3 OG-550 560 >2500 600 1000 

4 RG-850 860 >2500 1050 1540 

5 LP-1500 1540 >2500 1600 2500 

6 empty 250 400 

The output of the monochromator is coupled to the Si and the InGaAs diodes using 

Al and gold-coated off-axis ellipsoid mirrors, respectively, with 5:1 de-magnification of 

the exit slit. Both the Si diode and the PMT are used in DC-current measurement mode, 

and the InGaAs detector is used with a frequency-stabilized chopper wheel (not shown) 

and phase-sensitive detection techniques for better signal-to-noise ratios in the shortwave infrared wavelength region. The Si and the InGaAs photodiodes are placed on a 

computer-controlled translation stage for repeatability. The helium-neon laser (not 

shown) on the detector stage is used in the alignment of source to the optical axis of the 

spectroradiometer. For the long-term stability of the system responsivity, both the 

monochromator and the detector stage are purged using nitrogen gas boil-off from a 

liquid nitrogen reservoir to reduce the atmospheric absorption and to increase the longterm stability of the internal mirrors and gratings. The fore-optic section is purged with a 

positive overpressure of dry air to keep out the moisture and other contaminants which 

can degrade the foreoptics. 

 3.2 Performance Characterizations of the FASCAL 2 Facility 

A primary goal of the FASCAL 2 facility is the spectral irradiance calibration of 

1000 W FEL lamps with > 1000:1 signal-to-noise ratio from 250 nm to 2500 nm and 

subsequent spectral irradiance assignment to other lamps. To achieve the desired signalto-noise ratio, the spectral throughput of the spectroradiometer system has to be 

sufficient. The typical spectral irradiance of an FEL lamp at 50 cm is plotted in Fig. 7 
 

 15

1000

-0.5

0.0

0.5

10-1

100

101

102

103

 100*( Si- Smean ) * Smean-1

Wavelength [ nm ]

InGaAs Diode

Si Diode

PMT

 Spectral Irradiance [ 

μW / cm2 nm ]

Figure 7. The left axis denotes the percent differences from the mean of the spectral irradiances measured 

over a duration of 1 h. A total of three consecutive measurements were performed with the individual 

measurements denoted by squares, triangles, and circles. The right axis indicates the typical spectral 

irradiance of a 1000 W FEL lamp. The spectral irradiances were measured using the PMT (open), the Si 

diode (solid), and the InGaAs diode (open-crossed). 

along with the percent change in the spectral irradiance response of the spectroradiometer 

found using the three detectors. Each detector is used to measure the spectral irradiance 

of an FEL lamp fixed at a distance of 50 cm and current-stabilized at 8.2 A. The lamp is 

measured using each detector 3 times over a time period of ≈ 1 h. The percent 

differences of the individual signals from the mean, 

 

∑

∑ ⎟

⎠

⎞ ⎜

⎝

⎛

⋅ −

Δ = n

i

i

n

i

i i

S

n

S

n

S

S

1

1 100

, (8) 

are plotted in Fig. 7 using the PMT, Si, and InGaAs photodiodes. 

The spread in the signals below 300 nm is due to the combined effects of the 

instability of the FEL lamp and the low signals, but the spread in the signals is still well 

below the total uncertainty of the spectral irradiance scale in this spectral region. 

Although the PMT is sensitive to 600 nm, the Si diode is the preferred detector from 350 

nm to 1100 nm due to its lower noise and better temporal stability. Since the Si diode is 

temperature stabilized, any changes in the responsivity due to the temperature-dependent 

band-gap shift are minimized. In Fig. 7, the measurements with the extended-InGaAs 

diode show greater fluctuations, especially near 2400 nm. Since the foreoptics of the 

monochromator is not purged, the increase in the differences of the signals at 1400 nm 
 

 16

and at 1800 nm is due to the presence of water-vapor absorption at these wavelengths 

leading to increased fluctuations in the measured signals. With the exceptions of the 

measurements at 1400 nm, 1800 nm, and 2400 nm, our goal of achieving a signal-tonoise ratio of 1000:1, as determined by the standard uncertainty of the measurement at a 

set wavelength, is met. 

The wavelength accuracy is critical, particularly in the ultraviolet wavelength 

region where the slope of the spectral irradiance with respect to wavelength is especially 

steep. The uncertainties in the spectral irradiance due to the wavelength uncertainty can 

be estimated by approximating the spectral shape of the FEL lamp with a 3000 K 

blackbody. Using the Wien approximation, the derivative with respect to wavelength is 

λ

λ

λ

d 5 d c2 ⎟

⎠

⎞ ⎜

⎝

⎛ = − L T

L

, (9) 

where cB

2B is the second radiation constant, T, temperature, and λ, wavelength. The 

wavelength accuracy of the spectroradiometer was checked using low-pressure Hg, Ne, 

and Ar spectral-line lamps which were placed into an integrating sphere to fill the 

entrance optics of the monochromator. The residuals of the linear fit to the wavelength 

calibrations are shown in Fig. 8. The wavelength uncertainties are found to be less than 

100 200 300 400 500 600 700 800 900 1000

-0.2

-0.1

0.0

0.1

0.2

Residuals [ nm ]

Wavelength [ nm ] 

Figure 8. The residuals of the linear fit to the wavelength calibrations performed using various lowpressure lamp sources for the wavelength region from 200 nm to 1000 nm. 

± 0.1 nm (k=2) from 200 nm to 1000 nm. The residuals of the linear fits for the shortwave infrared wavelength region are shown in Fig. 9. Higher-order polynomials were 

also used to correct the wavelength errors, but did not lead to significant reduction in the 

wavelength uncertainties. The wavelength uncertainties are less than ± 0.15 nm (k=2) 

from 1000 nm to 2500 nm. The spectral irradiance uncertainty due to a 0.1 nm 

wavelength error is estimated from Eq. 2 to be < 0.6 % at 250 nm, and the spectral 

irradiance uncertainty decreases with wavelength to < 0.1 % past 500 nm since the 
 

 17

spectral irradiance of the FEL lamp peaks near 900 nm. The wavelength positioning is 

reproducible to ± 0.015 nm with changes in the gratings using the motorized grating 

turret. 

600 900 1200 1500 1800 2100 2400

-0.2

-0.1

0.0

0.1

0.2

Residuals [ nm ] 

Wavelength [ nm ] 

Figure 9. The residuals of the linear wavelength fit to the wavelength calibrated using various spectral line 

sources for the near IR wavelength region. 

 Since each NIST-issued spectral irradiance standard is measured at against one 

working standard lamp in one of the four stations, the invariance of the spectral 

irradiance of the standards with respect to changing lamp stations was also examined. 

The measurements with different power supplies and shunt resistors guard against 

possible systematic errors in the current and the power supply in the calibration of the 

standard. The use of different lamp stations also makes the spectral irradiance 

measurement eliminates systematic effects of scattered light and lamp positioning. The 

measurement of a common FEL lamp in each of the four stations shows reproducibility to 

0.1 % in the wavelength region from 350 nm to 1000 nm. 
 

 18

4. Uncertainty Analysis of the Spectral Irradiances Issued on FEL Lamps 

The discussion of the uncertainties associated with the detector-based spectral 

irradiance scale realization is separated into parts. Since the absolute radiance 

temperature determination of the HTBB is performed with filter radiometers with peak 

spectral responsivities near 550 nm, the expanded uncertainties in the spectral irradiance 

measurement at 550 nm is first discussed. The spectral irradiance uncertainties are 

converted into temperature uncertainties using the derivative of the Wien approximation. 

The Wien approximation is used since the measurements with the FRs are performed at 

short-wavelengths from the peak wavelength of the 3000 K Planck spectral radiance. 

The uncertainties of the spectral irradiances of the primary working standards (PWS) are 

assigned. Finally, the expanded uncertainties of the issued standards or the lamps-under 

test (LUT) are assigned with additional uncertainty added to account for the temporal 

changes of the PWS. 

4.1 Uncertainties of the HTBB detector-based temperatures 

The uncertainties associated with the detector-based temperature determinations 

of the HTBB can be found from the uncertainty analysis of Eq. (1) as shown in Table 3. 

The individual components are listed in descending order of importance, with the 

uncertainty due to the spectral power responsivity dominating. Additional sources of 

uncertainty from the alignment and aperture area measurements are small. The expanded 

spectral irradiance responsivity uncertainty at 550 nm of 0.26 % leads to an expanded 

temperature uncertainty of 0.86 K, at 2950 K. The increase in the uncertainties in the 

ultraviolet region in line 1 of Table 4 is due to the sensitivity of the Planck radiance to 

temperature which is inversely proportional to wavelength. 

4.2 Uncertainties of the spectral irradiance realization to primary working 

standards 

Table 4 describes the additional uncertainties associated with the HTBB spectral 

irradiance including the components due to spectral emissivity, spatial uniformity, and 

temporal stability. Line 1 shows the expanded uncertainty of the spectral irradiance due 

to the 0.86 K expanded temperature uncertainty at 2950 K. The uncertainties due to the 

spectral emissivity in line 2 and the spatial uniformity uncertainty in line 3 of the HTBB 

are then assigned from the data in Fig. 3 where two different blackbodies were compared. 

The temporal stability of the HTBB component in line 4 has been measured as shown in 

Fig. 4 and also constantly monitored using the optical feedback at the rear of the cavity. 

The uncertainties in the alignment of the apertures and in the distance measurements are 

included in the geometric factor uncertainty in line 5. 

Lines 6 to 9 pertain to the transfer of the spectral irradiance to PWS using the 

spectroradiometer. The detectors used in the spectroradiometers have shown better than 

0.1 % (k = 2) stability during the spectral irradiance measurements, but in the ultraviolet 

wavelength region, the integrating sphere used to collect the irradiance can change in 

throughput due to changes in the spectral reflectance of the coating [T29T]. The increase in 

the uncertainty at 2400 nm is due to the stability of the spectroradiometer responsivity 
 

 19

from the performance of the InGaAs detector near its bandgap wavelength. In line 7, a 

substantial contribution to the total uncertainty comes from the uncertainty in the absolute 

wavelength, especially in the ultraviolet wavelength region where the responsivity 

changes rapidly, due to the spectrally dependent coatings on mirrors in the 

spectoradiometer. To minimize this contribution, the wavelength drive of the 

spectroradiometer has an absolute optical encoder attached to the shaft, and piece-wise 

continuous polynomial corrections are applied to achieve ± 0.05 nm standard uncertainty 

in the wavelength. 

4.3 Uncertainties of the issued spectral irradiance standards 

For determination of the uncertainties on the issued standards, additional 

components arising from the lamp-to-lamp transfer and long-term stability of the working 

standards are added in lines 10 and 11. An additional increase in the total uncertainties 

arises from the possible temporal drift of the PWS. All lamps standards are subjected to 

screening procedure for temporal drift, and lamps that change by more than 0.5 % at 650 

nm over the duration of 24 operational hours are rejected from further evaluation as 

possible standards. The temporal drift is found to be inversely proportional to the 

wavelength, and is accordingly larger at the shorter wavelengths. Figure 10 plots the 

expanded uncertainties of the PWS along with the total uncertainties of the issued 

spectral irradiance standards with respect to SI units. The increase in the ultraviolet 

wavelength region and the increase in the uncertainties at 2400 nm is discussed above. 

0 500 1000 1500 2000 2500

0.0

0.5

1.0

1.5

2.0

Uncertainties ( 

k=2 ) [ % ]

Wavelength [ nm ]

 Uncertainty of PWS

 Overall uncertainty

Figure 10. The expanded uncertainties of the PWS and the total uncertainties of the issued spectral 

irradiance standards with respect to SI units. 
 

 20

To determine whether the uncertainties have been correctly determined, data from 

separate independent scale realizations of an FEL lamp (F210) were analyzed. Figure 11 

shows the percent differences from the mean in the detector-based spectral irradiance of 

the lamp with three independent assignments from 250 nm to 900 nm and from three 

other separate assignments 800 nm to 2400 nm over four separate days. The spectral 

irradiance assignments show that the three independent scale realizations for a particular 

wavelength region are all within the assigned (k = 2) expanded uncertainties of the 2000 

spectral irradiance scale. The temperature of the HTBB was determined on each of the 

days during the realization and the spectral irradiance responsivity was assigned about 30 

min after a temperature assignment using the filter radiometers. The separate spectral 

0 500 1000 1500 2000 2500

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

 Difference from mean [ % ]

 Wavelength [ nm ]

Figure 11. The percent differences from the mean of three separate, independent spectral irradiance scale 

realizations performed on four separate days. The differences are shown with the assigned expanded 

uncertainties of the working standards for the detector-based spectral irradiance scale. 

irradiance assignments are all within the expanded uncertainties. 

4.4 International comparisons to support the NIST assigned uncertainties 

The NIST assigned uncertainties are used in international intercomparisons of 

radiometric scales such as the CCPR k1-a key comparison where the spectral irradiance 

scales of 13 different countries were compared using 1000 W FEL lamps as the 

comparison artifacts [T30T]. The results of the measurements are compared using a 

weighted mean with the weights being the inverse of the respective national measurement 

laboratory’s (NMI) uncertainties squared. The spectral irradiances measured by the 

individual NMI are then compared against the weighted mean to determine the degrees of 

equivalence between the respective NMIs and also to determine if the differences from 

the weighted world mean or the Key Comparison Reference Value (KCRV) are within 
 

 21

the expanded uncertainties stated by the respective NMI. The detailed results of the 

comparison can be seen in Ref. 29. The differences of the NIST measurements from the 

KCRV were all within the expanded NIST uncertainties. 

Table 4. Uncertainty components for the HTBB temperature determination. At the 

HTBB temperature of 2950 K, an irradiance response uncertainty of 0.26 % corresponds 

to a temperature uncertainty of 0.86 K (k = 2). 

Source of uncertainty 

[ 550 nm ] 

Fractional uncertainty Expanded uncertainty [%] 

(k = 2) 

Spectral power responsivity, FR 

R

ΔR 0.22 

Solid angle factor, HTBB/FR 0.026 

Area of detector aperture 

A

ΔA 0.02 

Area of HTBB aperture 

A

ΔA 0.02 

Measurement precision, 

HTBB/FR 

 0.006 

Amplifier gain 

G

ΔG 0.006 

Combined expanded uncertainty 

[ k = 2 ] 

 0.26 
22

Table 5. Uncertainty Budget for Spectral Irradiance Calibrations Using FASCAL 2.

Relative Expanded Uncertainties (k 

S ource of Uncertainty 250 

nm 

350 

nm 

450 

nm 

555 

nm 

654.6 

nm 

900 

nm 

1600 

nm 

1. HTBB temperature uncertainty (0.86 K at 2950 K) (B) 0.57 0.41 0.32 0.26 0.22 0.16 0.09 2. HTB B spectral emissivity (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 3. HTBB spatial uniformity (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 4. HTBB temporal stability (0.1 K / h) (B) 0.07 0.05 0.04 0.03 0.03 0.02 0.01 5. Geometric factors in irradiance transfer (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 6. Spectroradiometer responsivity stability (B) 0.60 0.60 0.30 0.30 0.30 0.30 0.30 7. Wavelength accuracy (0.1 nm) (B) 0.58 0.26 0.13 0.07 0.04 0.01 0.01 8. Lamp/spectroradiometer transfer (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 9. Lamp current stability (B) 0.07 0.05 0.04 0.03 0.03 0.02 0.02 Total uncertainty of the primary working standards 1.03 0.80 0.50 0.45 0.43 0.40 0.37 10. Lamp -to-lamp transfer (A) 0.50 0.30 0.20 0.20 0.20 0.20 0.20 11. Long -term stability of primary working standards (B) 1.31 0.94 0.73 0.59 0.50 0.36 0.20 Overall uncertainty of the test with respect to SI units 1.74 1.27 0.91 0.77 0.69 0.57 0.47 

Note: The Type A or Type B evaluation of the uncertainty is indicated in parentheses.
 

 23

5. Future Work 

The development of FASCAL 2, a dedicated spectral irradiance realization and 

calibration facility, and the implementation of the detector-based spectral irradiance scale 

have lead to lower total uncertainties and faster calibration throughput of the spectral 

irradiance standards. Currently, lamps in 4 stations can be turned on or off with 

computer control enabling automated calibrations with the only manual operation that of 

placing the lamps in their mounts. The implementation of “Once is Enough” program [7] 

of having quality-control charts and eliminating repetitive measurements requires even 

better understanding of the calibration process so that the low uncertainties can be 

routinely maintained. One of the best ways to ensure that the calibration standards are 

within the specified uncertainties is to measure the same quantity with two different 

realization chains to compare the different ways of approaching the same quantity. This 

approach can help discover systematic sources of uncertainties which can be unknown 

with just a single approach. 

The assigned spectral irradiances derived from the HTBB can also validated by 

direct measurements with a calibrated filter radiometer. The filter radiometers can be 

calibrated for spectral irradiance responsivity from the NIST Spectral Irradiance and 

Radiance responsivity Calibrations using Uniform Sources (SIRCUS) facility [T31T] using 

monochromatic radiation which overfills the entrance aperture of the filter radiometers. 

If filter radiometers can be developed to cover a selected wavelength region to measure 

every FEL lamp operated in FASCAL 2, their measured irradiance response with their 

calculated irradiance response can be compared. If the entrance aperture is placed at 

exactly 50 cm away from the FEL mount, aligned to the optical axis, then the calculated 

irradiance response, vB

CB, is given by, 

vC = G∫(sE ⋅ E)dλ (10) 

where G is the preamplifier gain in volts/amp, sB

EB is the measured absolute spectral 

irradiance responsivity, and E is the assigned spectral irradiance from FASCAL 2. Since 

the absolute spectral irradiance responsivity can be determined with expanded 

uncertainties of < 0.1 % in the visible wavelength region, then the calculated irradiance 

response should be in agreement with the measure response to within the uncertainties of 

the NIST assigned values in Table 4. We are in the process of implementing the above 

procedure. 

Acknowledgments 

 The authors gratefully acknowledge the help and encouragement of Gerald Fraser, 

Robert Saunders and Al Parr of the Optical Technology Division at all stages of this 

project. The authors would like to also acknowledge the assistance of Tom Larason and 

George Eppeldauer in the development and the characterization of the filter radiometers 

used in the scale realization. The authors also acknowledge the assistance from Jim 

Proctor in setting up the FASCAL 2 facility. 

 
 

 24

*Certain commercial equipment, instruments, or materials are identified in this paper to 

foster understanding. Such identification does not imply recommendation or 

endorsement by the National Institute of Standards and Technology, nor does it imply 

that the material or equipment are necessarily the best available for the purpose. 

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spectral response using the National Institute of Standards and Technology highaccuracy cryogenic radiometer, Applied Optics 35, 4392-4403 (1996). 

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T4T. Y. Ohno, Improved photometric standards and calibration procedures at NIST, J. Res. 

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thP

 Edition, Bureau International des Poids et 

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T10T. G. Meister, P. Abel, R. Barnes, J. Cooper, C. Davis, G. Fargion, R. Frouin, M. Godin. 

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T11T. W.W. Coblentz, Bull. Bur. Stds. 11, 87 (1914). 

T12T. R. Stair, W. E. Schneider and J. K. Jackson, A New Standard of Spectral Irradiance, 

Applied Optics 2, 1151-1154 (1963). 

T13T. R. Stair, W.E. Schneider and W.B. Fussell, The New Tungsten-Filament Lamp 

Standards of Total Irradiance, Applied Optics 6, 101-105 (1967). 

T14T. R.D. Saunders and J. B. Shumaker, NBS Tech Note, 594-13, 1977. 
 

 25

T15T. M. Suzuki and N. Ooba, Metrologia 12, 123 (1976). 

T16T. J.H. Walker, R.D. Saunders, J.K. Jackson, and K.D. Mielenz, J. Res. Natl. Inst. Stand. 

Technol. 96, 647-668 (1991). 

T17T. H.W. Yoon, C.E. Gibson, P.Y. Barnes, Realization of the National Institute of 

Standards and Technology Detector-based Spectral Irradiance Scale, Applied Optics

41, 5879-5890 (2002). 

T18T. E.R. Woolliams, N.P. fox, M.G. Cox, P.M. Harris and N.J. Harrison, The CCPR k1-a 

key comparison of spectral irradiance from 250 nm to 2500 nm: measurements, 

analysis and results, Metrologia 43, S98-S104 (2006).

T19T. T.R. Gentile, J.M. Houston, J.M. Hardis, C. L. Cromer A. C. Parr, National Institute 

of Standards and Technology high accuracy cryogenic radiometer, Applied Optics 35, 

1056-1068 (1996). 

T20T. J. Fowler and M Litorja, Geometric area measurements of circular apertures for 

radiometry at NIST, Metrologia 40, S9-S12 (2003).

T21T. H.W. Yoon, C.E. Gibson, Determination of radiance temperatures using detectors 

calibrated for absolute spectral power response, Proceedings of the TEMPMEKO99, 

J. F. Dubbeldam and M. J. deGroot, eds., NMI Van Swinden lab. Delft, Netherlands, 

1999, pp. 737-742. 

T22T. T.C. Larason, S.S. Bruce, A.C. Parr, Spectroradiometric detector measurements: part 

I- ultraviolet detectors and part II- visible to near-infrared detectors, NIST 

Measurement Services SP 250-41 (National Institute of Standards and Technology, 

Gaithersburg, MD, 1998).

T23T. V.I. Sapritsky, Blackbody radiometry, Metrologia 32, 411-418 (1996). 

T24T. P. Sperfeld, S. Galal-Yousef, J. Metzdorf, B. Nawo, and W. Moller, The use of selfconsistent calibrations to recover absorption bands in the black-body spectrum, 

Metrologia 37, 373-376 (2000). 

T25T. J.H. Walker, R.D. Saunders and A.T. Hattenburg, Spectral Radiance Calibrations, 

NBS Special Publication 250-1, U. S. Government Printing Office Washington 1987. 

T26T. A. Thompson, H.M. Chen, Beamcon II, a linearity measurement instrument for 

optical detectors, J. Res. Natl. Inst. Stand. Technol. 99, 751 (1994). 

T27T. H.W. Yoon, C.E. Gibson, Comparison of the absolute detector-based spectral 

radiance assignment with the current NIST-assigned spectral radiance of tungsten 

strip lamps, Metrologia 37, 429-432 (2000). 

T28T. H.J. Kostkowski, D.E. Erminy, A.T. Hattenburg, Advances in Geophysics 14, 111-

127 (1970).

T29T. D.R. Gibbs, F.J. Duncan, R.P. Lambe and T.M. Goodman, Ageing of materials under 

intense ultraviolet radiation, Metrologia 32, 601-608 (1996). 
 

 26

T30T. http://kcdb.bipm.org/ 

T31T. S.W. Brown, G.P. Eppeldauer, K.R. Lykke, NIST Facility for Spectral Irradiance and 

Radiance Responsivity Calibrations with Uniform Sources, Metrologia 37, 579-582 

(2000).
Appendix A. Lamp Selection Process 

Before the FEL lamps are selected as spectral irradiance standards, the lamps are 

put through an aging and screening processes. Since lamps will typically become more

stable with operating hours, the aging process is to accelerate the long-term stable

behavior of the lamps by operating the lamps at slightly higher electrical power than their 

calibrated use. When the FEL lamps are obtained from the vendor, the lamps are aged by 

operating them at a constant voltage of 120 VDC, higher than their operating voltage, for 

4 hours. The lamps are also operated at constant current of 8.2 ADC for 48 hours. The 

lamps are then placed in brass holders and then potted using ceramic cement. 

A.1 Spectral Screening

The screening of the lamps is performed using a spectroradiometer. The lamps 

are measured using a double monochromator for the presence of spectral features. The 

lamps are scanned from 250 nm to 400 nm every 0.1 nm with 0.02 mm entrance slit 

width resulting in ~ 0.04 nm bandwidth. In order to increase the measured signal this

procedure is performed with a mirror in place of the integrating sphere. The result of 

such a scan is shown in Fig. 1. Although in the past the presence of such lines would 

250 275 300 325 350 375 400

0

1

2

3

4

5

6

Emission

Absorption 

Signal [ V ]

Wavelength [ nm ]

Figure A1. The spectral features from the FEL lamp measured using a double monochromator with

bandwidth of 0.04 nm. The step changes are due to the changes in the high-voltage bias of the 

photomultiplier tube. The emission doublets are due to the presence of aluminum inside the FEL. 

lead to rejection of any lamps which exhibit such features, at present, all lamps with the 

features are accepted since we are not able to find any lamps without the spectral 

features. The measurements are performed using a photomultiplier tube (PMT) and the 

abrupt changes in the signal at ~ 265 nm and at ~ 315 nm are due to the changes in the 

high-voltage bias of the PMT. The emission lines are indicated in Fig. 1 along with an 

absorption feature at ~ 280 nm. The measured emission lines along with the listed 

aluminum emission wavelengths from the CRC Handbook [1] are listed in Table 1. The 

 A1 
differences are within the uncertainties of the wavelength setting of the 

spectroradiometer. The aluminum is attributed to contamination of the tungsten filament

during the manufacturing process. The high operational temperature of the tungsten 

filament in the FEL lamp leads to thermal excitation of the aluminum resulting in the

spectral emission. 

Table A1. The measured wavelengths and the listed wavelengths from the CRC handbook. The 

differences are within the wavelength uncertainties of the spectroradiometer.

Measured [ nm ] CRC value [ nm ] Measured-CRC value 

[ nm ]

256.79 256.8 -0.01

257.49 257.51 -0.02

308.3 308.22 0.08

309.29 309.27 0.02

394.43 394.4 0.03

396.13 396.15 -0.02

A.2 Temporal stability check 

Lamps are measured for long-term temporal stability of the spectral irradiance at 

654.6 nm. These measurements are to ensure that lamps which are calibrated by NIST 

can maintain their calibrations over an extended period of time. The measurements are 

performed with the Si diode detector to maintain stable spectral irradiance responsivity. 

Any lamp calibrated by NIST must be stable to better than 0.5 % in spectral irradiance at 

654.6 nm over a 24 hour period. Figure A2 shows the voltage, current and the signal 

from a photometer monitoring an FEL lamp over a 48 h period. All the measured values 

are plotted as ratios to the initial value. Although the current held stable, the voltage can 

change leading to changes in the radiation. The optical output can be seen to generally 

correlated with the electrical power.

1.0100

0.9980

1.0000

1.0025

1.0050

1.0075

Current

Voltage 

Monitor

Monitoring Data

Figure A2. The optical power and the measured voltage across the FEL lamp under constant current

conditions. The values plotted are ratioed to the initial values. This FEL lamp would be accepted under the 

current NIST screening criteria.

Most lamps are stable to 0.3 % over a 24 h time period. The stability of the responsivity 

of the spectroradiometer is < 0.1 % over the time period. FEL lamps typically exhibit a 

slow drift of the spectral irradiance over the monitoring time duration. Rejected lamps 

change at faster rates or exhibit bi-stable outputs. An example of a lamp showing bistable output is shown in Fig. A3. Although the current to the lamp is held stable, the 

 A2 
voltage fluctuates leading to a fluctuation in the optical output. The lamp seems to 

recover after 24 hours. 

1.0100

0.9960

1.0000

1.0050

Current

Voltage 

Monitor

Monitoring Data

Figure A3. The optical power and the measured voltage across the FEL lamp under constant current

conditions. The values plotted are ratioed to the initial values. This FEL lamp would not accepted under 

the current NIST screening criteria.

Although the changes of the lamp due to slow aging are expected to be faster at the

shorter wavelengths, the long-term temporal stability screenings are performed at 654.6 

nm since the radiance temperature realizations are performed at this wavelength. 

Currently about 90 % of the lamps tested meet this requirement.

A.3 Goniometric Scans 

Since the FEL lamps are sometimes used outside the calibrated 1 cm2

 area in the 

direct optical axis of the alignment jig, the non-uniformity of the projected irradiance is 

measure by rotation and tilt of the FEL lamp placed in a goniometric cradle. A 

representative goniometric map is shown in Fig. A4. For the lamps to pass goniometric 

-8 -6 -4 -2 0 2 4 6 8

6

4

2

0

-2

-4

-6

Percent different from center

Horizontal Angle [ ψ ]

Vertical An

gle [ 

Φ ]

-7.5

-6.5

-5.5

-4.5

-3.5

-2.5

-1.5

-0.5

0.5 1.0

Figure A4. The percent differences in the spectral irradiances at 650 nm with angular tilts of the FEL 

lamp. The lamps are uniform with respect to horizontal rotation and are much more sensitive to the vertical 

rotation. This particular lamp shows < 1.0 % change in the spectral irradiance with 1 ° change in any

direction. 

 A3 
screening, FEL lamps must not exhibit more than 1 % change in the spectral irradiance at 

654.6 nm as measured with the integrating sphere in place with a ± 1.0° rotation in any 

direction. Currently, about 95 % of the lamps measured meet this selection criterion. 

Upon special request FEL lamps can be further measured at greater angles. Contour plot 

of the percent difference of the spectral irradiance from the center is shown in Fig. 4.

The irradiance is measured as a function of the vertical and horizontal angle of the FEL 

lamp. The figure shows the large changes in the spectral irradiance with respect to the 

vertical angle and the slow changes with the horizontal angle. Since the FEL lamp is 

much more physically symmetric with respect to horizontal rotation, the relative 

insensitivity of the spectral irradiance is shown.

 

1. CRC Handbook of Chemistry and Physics, 62nd Edition 1982, R.C Weast and M.J. 

Astle, eds., CRC Press, Boca Raton, Florida, p. E206. 

 A4 
Appendix B. Orientation dependence of the FEL lamps 

Due to the electrical heating induced by the close to ~ 1000 W of electrical power

dissipated by the FEL lamps, the lamp filament and the envelope are at high operating 

temperatures. Since the lamps are operated in air, steady-state temperature of the lamp 

envelope and the filament are dependent upon the air convection. Measurements of the

spectral irradiance with changing FEL orientation have shown that the orientation of the 

FEL lamp can affect the spectral irradiance output by changing the filament temperature. 

A fixture consisting of the FEL lamp and a filter radiometer was constructed so that the

FEL lamp could be operated in each of the three orientations to the reference aperture of 

the filter radiometer as shown in Fig. 1. Since the mechanical mount of the fixture could 

be turned in each of the different orientations as a system, the rigid supports allowed 

reproducible changes in the lamp orientations. The filter radiometer consisted of Si

diodes in a trap configuration with a manually controlled filter wheel to place various 

filters into the optical path. The filters consisted of narrow-band interference filters from

above 300 nm to close to 1000 nm. 

Vertical Side Horizontal

Optic 

Axis Radiometer

Aperture

Figure B1. The respective orientations of the FEL lamp during its measurements. A specially designed 

fixture allowed rigid support of the lamp and the radiometer during the different changes in the

orientations. 

 B1 
The lamp and the filter radiometer were placed to have the FEL in the vertical geometry.

The initial signals from the filter radiometer was measured and recorded for comparisons 

with the later measurements. The lamp was turned off and removed. The entire 

configuration was rotated to the side position as shown in Fig. 1 and then the lamp placed 

back for measurements with the filter radiometer. The results of the filter radiometer 

measurements are shown in Fig. B2. Figure B2 shows the ratios of the signals to the 

initial vertical signals. The vertical signals, as shown by the triangles in Fig. B2, 

measured after the side and the horizontal orientations indicate that the FEL and the filter

radiometer combined is reproducible to < 0.5 % in this spectral range. The side and the 

horizontal orientations show spectrally dependent drop in the spectral irradiance 

indicative of a change in the temperature of the filament and the lamp envelope. If the

direction of the long axis of the lamp causes more effective convective cooling, then such 

cooling could be the cause of the greater change in the shorter wavelengths as observed 

in Fig. B2. It is not clear why there should be differences between the side and the 

horizontal configurations. 

300 400 500 600 700 800 900 1000

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

1.01

Ratio to Initial Vertical Signals

Wavelength [nm]

Side

Horizontal

Vertical

Figure B2. The signal ratios to the initial vertical orientation. After the side and the horizontal 

configurations, the lamp was returned to the vertical position and shows that the lamp is repeatable to

within < 1 % from 300 nm to 900 nm. 

The above study demonstrates the dependence of the spectral irradiance on the angular

orientation of the FEL lamp. If the uncertainties as issued by NIST are to be propagated 

without a substantial increase, then any changes to the spectral irradiances caused by a 

change in the mounting configuration should be assessed. 

 B2 
Appendix C. Physical alignment of the FEL lamp 

This section describes the mounting and the alignment procedure for the NIST 

FEL lamps. The FEL lamps from the manufacturers are mounted into brass adapters 

which are in turn attached to stainless steel posts for incorporation into NIST lamp

assemblies. The alignment of the optical axis is performed using a lamp jig shown in 

Fig. C1. The lamp mount is first prepared by assembling stable, opto-mechanical 

plate this

fixture S/N

detector.

away from

side.

plate on

FEL alignment

Lamp S/N

this side

50.0 cm

Aperture plane

fixture.

face of FEL

measurement

made to this

alignment

Distance

Rear Base 

Baffle Plate

Front Baffle

Middle Baffle

Figure C1. The physical alignment of the FEL lamp in an optomechanical mount in NIST FASCAL 2.

The mount should have enough degrees of freedom so that the optical axis can be aligned. The lamp serial

number (S/N) should be on the side facing away from the radiometer. 

components as shown in Fig. C1. First the lamp jig is mounted and the lamp fixture is 

adjusted so that the lamp jig is level with respect to the ground by using a spirit level. 

Then a laser is placed behind the lamp jig so that the laser is perpendicular to the lamp jig 

and centered on the opening of the integrating sphere. The optical axis is defined by 

attaching a flat glass plate to the opening of the integrating sphere at the left and retroreflecting back to the alignment mark on the lamp jig. The distance of 50.00 cm is set 

between the opening of the integrating sphere and the front surface of the lamp jig. The 

front surface of the lamp jig is coincident with the front surface of the stainless steel posts

of the FEL lamp. At NIST, two baffles around the optical axis are used to reduce the

 C1 
stray light since the integrating sphere receiver is sensitive to a wide-angular field of 

view. A third, rear-base baffle is used to cover the slightly reflective base of the FEL 

lamp from the receiver. The height of the rear baffle is adjusted until center of the lamp

base is aligned with the lower edge of the integrating sphere opening. The base of the 

lamp with the serial number carved into the brass plate is placed on the side away from 

the opening of the spectroradiometer. 

 C2 
 D1 

Appendix D. Atmospheric absorption and FEL interpolations 

D1. Atmospheric absorption 

Currently, the spectral irradiance scale is realized on FEL lamps at 35 separate 

wavelengths from 250 nm to 2400 nm. In the ultraviolet wavelength region from 250 nm 

to 400 nm, due to possible rapid changes in the spectral irradiance from current instability 

and lamp aging, the spectral irradiances are assigned at every 10 nm. Past 400 nm, the 

realizations are performed at selected wavelengths chosen to avoid atmospheric 

absorption. The 1 m path atmospheric transmittance for standard, sea-level altitude 

conditions [T

1

T] along with the spectral irradiances from an FEL lamp are shown in Fig. 1. 

The absorption is from the presence of water and COB

2B and will vary with humidity and 

other atmospheric conditions. Since the FEL lamps are operated standard laboratory 

environments, if the calibrated wavelengths of the spectral irradiances are coincident with 

the atmospheric absorption, then the stability of the spectral irradiance will be reduced. 

The spectral irradiances at the wavelengths where the atmospheric absorption will reduce 

the stability are purposely avoided. 

0.0

0.2

0.4

0.6

0.8

1.0

0 500 1000 1500 2000 2500

0

5

10

15

20

25

Atmospheric Transmittance (1 m path)

Spectral Irradiance [ 

μW /cm2 nm ]

Wavelength [ nm ]

Figure D1. The atmospheric transmittance for a 1 m path at standard sea level conditions along with the 

spectral irradiances of an FEL lamp. The spectral irradiance realizations at wavelengths coinciding with 

atmospheric absorption are purposely avoided. 
 D2 

D2. FEL interpolations 

FEL lamps are used in photometry to determine correlated color temperatures and 

distribution temperatures. The lamps are also sometimes used to realize other 

photometric units such as the lumen. Since the photopic response or the spectral 

luminous efficiency function for photopic vision and the CIE (Commision Internationale 

de l’Éclairage) color matching functions for chromaticity are given at 1 nm intervals [T

2

T], 

the use of FEL lamps under such conditions requires interpolation of the spectral 

irradiances at finer wavelength intervals than those realized. Two of the interpolation 

approaches are described below. Both of these interpolations can be performed using a 

program <Fitirrad> [T

3

T] which can be provided, on request, by the Optical Technology 

Division of NIST. 

The spectral irradiance from the FEL lamp is determined by factors such as the 

temperature of the coiled-coil tungsten filament, the tungsten emissivity, the quartz lampenvelope transmittance and the physical structure of the filament. The spectral shape of 

the FEL lamp can be fitted by an interpolation function which is derived from Planck’s 

radiation law. The interpolation function used at NIST utilizes a 4P

thP

 order polynomialmodified Wien approximation, 

( ) ⎟

⎠

⎞ ⎜

⎝

⎛ = + ⋅ + ⋅ + ⋅ + ⋅ ⋅ +

T

E A A A A A A

λ λ λ λ λ λ λ 2

5

4 5

4

3

4

2

0 1 2

c / exp , (1) 

where λ is the wavelength, T is the fitted temperature, cB

2B is the second radiation constant, 

and AB

0B to AB5B are fitted parameters. The polynomial term accounts for the emissivity of 

the FEL lamp. Due to the possible oscillations, which can arise from fitting of high-order 

polynomials if the data grid is sparse, especially at the endpoints of the fitting, the 

spectrum is broken into spectral regions. Currently, for the NIST-issued program the 

spectrum is separated into three sections; 250 nm to 350 nm for the ultraviolet region, 

350 nm to 800 nm for the visible region, and 800 nm to 2400 nm for the near-infrared 

and the short-wave infrared region. Other, modified interpolation functions can be also 

used [T

4

T]. As observed from the atmospheric transmission shown in Fig. 1, interpolation 

through the wavelength region with absorption lines will lead to larger uncertainties. 

Since the polynomial fitting utilizes minimization of the chi-squared sum over the 

range of the fitted wavelengths, the resulting uncertainties of the interpolated values can 

have higher correlations with the spectral irradiances at other wavelengths [T

5

T]. To avoid 

additional increases in uncertainties arising from the correlations due to the fitting, the 

spectral irradiances can also be fit by natural cubic spline. The program issued by NIST 

has provisions for both types of fitting. The uncertainties of the interpolated values of the 

spectral irradiance is expected to increase by < 0.5 % (k = 2) depending on the region of 

the fit. 

 

T

1

T. L.S. Rothman, et al., Journal of Quantitative Spectroscopy and Radiative Transfer, 

vol. 96, pp. 139-204 (2005). 

T

2

T. Colorimetry, 3P

rdP

 Edition, CIE Publication 15, 2004. 
 D3 

 

T

3

T. Ftirrad.vbp (program provided by NIST for polynomial or cubic-spline fitting of 

spectral irradiances) 

T

4

T. L.K. Huang, R.P. Cebulla and E. Hilsenrath, New Procedure for interpolating NIST 

FEL lamp irradiances, Metrologia 35, 381-386 (1998). 

T

5

T. J. Gardner, Uncertainty Propagation for NIST Visible Spectral Standards, J. Res. Natl. 

Inst. Stand. Technol. 109, 305-318 (2004). 
E1 

Appendix E. Sample calibration report 

REPORT OF CALIBRATION 

39045C Spectral Irradiance Standard, 1000 W Tungsten Quartz-Halogen Lamp 

(250 nm to 2400 nm) 

for 

Osram Sylvania, Model # T6, Serial # F-000 

Issued to: 

Radiometric Systems Incorporated 

Attn.: Mr. Art Monk 

123 Calibration Court 

Measurement City, MD 00000-0000 

(See your Purchase Order No. AB123, dated March 28, 2011) 

1. Description of Calibration Item

A 1000 W, quartz-halogen lamp with a coiled-coil tungsten filament was calibrated by the 

National Institute of Standards and Technology (NIST) as a standard of spectral irradiance from 

250 nm to 2400 nm. The lamp is mounted in a medium bi-post base. The serial number is 

located on the rear of the lamp base opposite the side viewed by the spectroradiometer. 

Spectral scans of the lamp from 250 nm to 400 nm in 0.1 nm steps revealed emission lines at 

257 nm, 309 nm, and 395 nm when using a spectroradiometer with a spectral bandwidth that 

varies with wavelength from 0.04 nm at 250 nm to 0.08 nm at 400 nm. The intensities of these 

lines are as much as 20 % greater than the adjacent continuum. A decrease in the lamp output 

due to absorption was observed at 279 nm. This decrease can be as much as 20 % below the 

adjacent continuum. While data is reported at 280 nm, care should be taken when measurements 

are made near 279 nm. Historically, these emission lines and absorption bands have been known 

to change with burning time. This calibration was performed with a spectral bandwidth that 

varied from 4 nm to 8 nm. The emissions lines and absorption bands are not measurable with 

bandwidths larger than 1 nm. If your instrument has a narrow spectral bandwidth, checks should 

be made in the area of the emission lines and absorption band. 

Laboratory Environment: 

Temperature: 23 °C ± 1 °C Relative Humidity: 23 % ± 5 % 

Calibration Date: March 31, 2011 

NIST Test No: 685/123456-11 Page 1 of 6 
E2 

REPORT OF CALIBRATION Manufacturer: Osram Sylvania 

39045C Spectral Irradiance Standard, 1000 W Quartz-Halogen Lamp Model #: T6 

Radiometric Systems Incorporated Serial #: F-000

2. Description of Calibration

The lamp was calibrated in the new NIST Facility for Automated Spectroradiometric 

Calibrations (FASCAL 2) using the equipment and procedures described in Ref. [1]. The lamp 

was measured at a distance of 50 cm from the entrance aperture of the integrating sphere with an 

aperture area of 1.0027 cm2

. The sphere viewed approximately a 9 cm diameter target in the 

plane of the front surface of the lamp bi-posts. With this geometry, the entire lamp was viewed 

from the top of the lamp envelope down to the top half of the black lamp base. Light baffling 

was used between the lamp and the spectroradiometer integrating sphere to minimize effects of 

scattered light. The alignment of the lamp is described in the next paragraph. 

The lamp was mounted vertically, base down with the brass identification plate facing away 

from the spectroradiometer. An alignment jig was placed in the kinematic lamp socket and 

aligned. This was accomplished by placing a spirit level on top of the jig and then by adjusting 

the angle about the optical axis until the level was balanced. The alignment jig target area, 

which is indicated by cross hairs, is centered between the bi-posts and located 9.5 cm above the 

bottom of the jig bi-posts. This target area was centered vertically and horizontally onto the 

optical axis. The jig was set perpendicular to the optical axis by reflecting the spectroradiometer 

laser beam back onto itself. The distance along the optical axis from the target area surface to 

the surface of the sphere aperture was set at 50 cm. The target area surface is in the plane with 

the front surface of the bi-posts. This alignment procedure sets the alignment jig bi-posts relative 

to the optical axis of the spectroradiometer. The jig was removed and the lamp was placed in the 

aligned socket. 

The test lamp was spectrally compared to the following working standards: F-350, F-352, and 

F-353 to determine its spectral irradiance. The spectral irradiance values for this standard lamp 

were assigned relative to the 2000 NIST Spectral Irradiance Scale [2]. 

3. Results of Calibration

Table 1 and Figure 1 give the spectral irradiance of the test lamp versus the wavelength in nm. 

Table 2 gives the calibration uncertainties in percent relative to the International System of Units 

(SI Units). The relative expanded uncertainties (coverage factor k = 2) have a level of 

confidence of 95 %. Details on the estimation of these uncertainties are given in Ref. [2]. The 

NIST policy on uncertainty statements is described in Ref. [3]. 

Calibration Date: March 31, 2011 

NIST Test No: 685/123456-11 Page 2 of 6
E3 

REPORT OF CALIBRATION Manufacturer: Osram Sylvania 

39045C Spectral Irradiance Standard, 1000 W Quartz-Halogen Lamp Model #: T6 

Radiometric Systems Incorporated Serial #: F-000

4. General Information

To maintain the highest accuracy, keep the lamp envelope clean and have the lamp recalibrated 

periodically. Appropriate calibration schedules vary with lamp and application and are best 

determined by the user. 

The lamp is operated on DC power. The lamp polarity is indicated on the lamp base 

identification plate. 

The results of this calibration apply only to the lamp referenced in this report. This report shall 

not be reproduced, except in full, without the written approval of the Spectroradiometric Source 

Measurements Calibration Service. 

Prepared by: Approved by: 

Charles E. Gibson Eric L. Shirley 

Optical Technology Division For the Director, 

Physical Measurement Laboratory National Institute of Standards and Technology 

(301) 975-2329 (301) 975-2349 

References

[1] H. W. Yoon, J. E. Proctor, and C. E. Gibson, “FASCAL 2: A New NIST Facility for the 

Calibration of Spectral Irradiance Sources,” Metrologia, 40, S30-S34, (2003). 

[2] H. W. Yoon, C. E. Gibson, and P. Y. Barnes, “Realization of the National Institute of 

Standards and Technology Detector-based Spectral Irradiance Scale,” Applied Optics, 41, 

5879-5890, (2002). 

[3] B. N. Taylor and C. E. Kuyatt, “Guidelines for Evaluating and Expressing the 

Uncertainty of the NIST Measurement Results,” NIST Technical Note 1297 (2nd ed., 

1994). 

Calibration Date: March 31, 2011 

NIST Test No: 685/123456-11 Page 3 of 6 
E4 

REPORT OF CALIBRATION Manufacturer: Osram Sylvania 

39045C Spectral Irradiance Standard, 1000 W Quartz-Halogen Lamp Model #: T6 

Radiometric Systems Incorporated Serial #: F-000

Table 1. Spectral Irradiance at 50 cm 

Lamp current at 8.200 A DC 

Wavelength 

[nm] 

Spectral 

Irradiance 

[μW cm-2 nm-1] 

Spectral 

Irradiance 

[W cm-3] 

Wavelength 

[nm] 

Spectral 

Irradiance 

[μW cm-2 nm-1] 

Spectral 

Irradiance 

[W cm-3] 

250 2.251E-02 2.251E-01 555 1.201E+01 1.201E+02 

260 3.901E-02 3.901E-01 600 1.509E+01 1.509E+02 

270 6.441E-02 6.441E-01 654.6 1.838E+01 1.838E+02 

280 9.959E-02 9.959E-01 700 2.065E+01 2.065E+02 

290 1.507E-01 1.507E+00 800 2.376E+01 2.376E+02 

300 2.177E-01 2.177E+00 900 2.466E+01 2.466E+02 

310 3.071E-01 3.071E+00 1050 2.316E+01 2.316E+02 

320 4.176E-01 4.176E+00 1150 2.126E+01 2.126E+02 

330 5.563E-01 5.563E+00 1200 2.019E+01 2.019E+02 

340 7.255E-01 7.255E+00 1300 1.803E+01 1.803E+02 

350 9.268E-01 9.268E+00 1540 1.315E+01 1.315E+02 

360 1.164E+00 1.164E+01 1600 1.213E+01 1.213E+02 

370 1.440E+00 1.440E+01 1700 1.056E+01 1.056E+02 

380 1.749E+00 1.749E+01 2000 6.980E+00 6.980E+01 

390 2.102E+00 2.102E+01 2100 6.086E+00 6.086E+01 

400 2.490E+00 2.490E+01 2300 4.674E+00 4.674E+01 

450 4.972E+00 4.972E+01 2400 4.124E+00 4.124E+01 

500 8.155E+00 8.155E+01 

For reference only: The voltage drop across the lamp during the calibration was 113.13 V. 

Calibration Date: March 31, 2011 

NIST Test No: 685/123456-11 Page 4 of 6 
E5 

REPORT OF CALIBRATION Manufacturer: Osram Sylvania 

39045C Spectral Irradiance Standard, 1000 W Quartz-Halogen Lamp Model #: T6 

Radiometric Systems Incorporated Serial #: F-000 

Figure 1. Calibration results of 1000 W Quartz Halogen Lamp 

Calibration Date: March 31, 2011 

NIST Test No: 685/123456-11 Page 5 of 6 

0

5

10

15

20

25

30

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

Spectral Irradiance [

μW cm-2 nm-1]

Wavelength [nm]
E6 

REPORT OF CALIBRATION Manufact

39045C Spectral Irradiance Standard, 1000 W Quartz-Halogen Lamp Radiometric Systems Incorporated 

Table 2. 2000 Spectral Irradiance Scale Uncertainties of the Primary Working Standards and the T

Source of Uncertainty 

Relative Expanded Uncertainties (k 

250 

nm 

350 

nm 

450 

nm 

555 

nm 

654.6

nm 

900 

nm 

1600

nm 

2

1. HTBB temperature uncertainty (0.86 K at 2950 K) (B) 0.57 0.41 0.32 0.26 0.22 0.16 0.09 02. HTBB spectral emissivity (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 03. HTBB spatial uniformity (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 04. HTBB temporal stability (0.1 K / h) (B) 0.07 0.05 0.04 0.03 0.03 0.02 0.01 05. Geometric factors in irradiance transfer (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 06. Spectroradiometer responsivity stability (B) 0.60 0.60 0.30 0.30 0.30 0.30 0.30 07. Wavelength accuracy (0.1 nm) (B) 0.58 0.26 0.13 0.07 0.04 0.01 0.01 08. Lamp/spectroradiometer transfer (B) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 09. Lamp current stability (B) 0.07 0.05 0.04 0.03 0.03 0.02 0.02 0Total uncertainty of the primary working standards 1.03 0.80 0.50 0.45 0.43 0.40 0.37 010. Lamp-to-lamp transfer (A) 0.50 0.30 0.20 0.20 0.20 0.20 0.20 011. Long-term stability of primary working standards (B) 1.31 0.94 0.73 0.59 0.50 0.36 0.20 0Overall uncertainty of the test with respect to SI units 1.74 1.27 0.91 0.77 0.69 0.57 0.47 0

Note: The Type A or Type B evaluation of the uncertainty is indicated in parentheses. 

Calibration Date: March 31, 2011 NIST Test No: 685/123456-11 
F1 

Appendix F. Irradiance Calibration Procedures Manual 

Irradiance 

Calibration Procedures Manual 

9 cm

View half way down base 

Baffle

Integrating sphere 

Lamp 
F2 

Irradiance Calibration Procedure 

IRR-CP-TOC-Table of Contents 

Table of Contents 

0. Safety Precautions (IRR-CP-IRR0) 

1. FASCAL2 Data Acquisition (DAQ) Program Operation (IRR-CP-IRR1) 

2. Quartz Halogen Lamp (QHL) Alignment (IRR-CP-IRR2) 

3. Quartz Halogen Lamp (QHL) Operation (IRR-CP-IRR3) 

4. High Temperature Blackbody (HTBB) Alignment (IRR-CP-IRR4) 

5. High Temperature Blackbody (HTBB) Operation (IRR-CP-IRR5) 

6. Filter Radiometer (FR) Alignment (IRR-CP-IRR6) 

7. Spectral Irradiance Scale Realization (IRR-CP-IRR7) 

8. Spectral Irradiance Calibration (IRR-CP-IRR8) 

9. Spectral Irradiance Data Reduction (IRR-CP-IRR9) 

10. Calculate the Correlated Color Temperature (CCT) and Luminous Intensity (LI) from 

Spectral Irradiance Data (IRR-CP-IRR10) 

11. Reset Linear Encoder (IRR-CP-IRR11) 

12. Goniometric Scan (IRR-CP-IRR12) 

13. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 11-Jul-06 C. Gibson 1 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-TOC 1.0 11-Jul-06 C. Gibson 1 of 1 IRR-CP-TOC Table of Contents 

v1.doc 
F3 

Irradiance Calibration Procedure 

IRR-CP-IRR0-Safety Precautions 

Safety Precautions

Safety glasses are required in the lab depending on task performed. 

The following hazards have been identified in this lab. Safety measures are in place to reduce 

the risk of injury from the hazards below. 

BRIGHT SOURCE

Avoid staring at the source 

Retina damage possible 

If source viewing is necessary, then use the correct neutral density filter 

BURN

Keep body and clothes away 

COLLISION

Keep the source table path clear 

Do not hang cables from source table 

ELECTROCUTION

High voltage connections present 

Do not touch electrical parts 

Have a 2nd party present when working on a high power/voltage source 

LASER

Retina damage from viewing the direct and indirect laser beam, and skin burns if the laser is 

powerful enough 

Contain or block laser beam and turn off when not in use 

If the laser beam is powerful enough and not contained then laser glasses/goggles are required. 

Do not wear reflective items that may fall into the laser beam 

OZONE

Avoid long exposure and get plenty of fresh air 

Over exposure to ozone can cause head aches 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR0 1.0 08-Jun-06 C. Gibson 1 of 2 IRR-CP-IRR0 Safety 

Precautions v1.doc 
F4 

Irradiance Calibration Procedure 

IRR-CP-IRR0-Safety Precautions 

UV

Avoid skin and eye exposure 

Can burn skin and eyes 

Symbols, similar to the one below, are used throughout this document to alert the operator to 

potential hazards. 

LASER

Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 08-Jun-06 C. Gibson 2 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR0 1.0 08-Jun-06 C. Gibson 2 of 2 IRR-CP-IRR0 Safety 

Precautions v1.doc 
F5 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

FASCAL2 Data Acquisition (DAQ) Program Operation

1. DAQ program (FEL Transfer.vi) 

1.1. The DAQ program communicates with the Lamp Current Control program (see IRR-CPIRR3) to ramp up the lamp, waits 20 minutes for the lamp to stabilize, measures the 

lamp and then ramps down the lamp. Measurements are performed for the lamps 

entered into the DAQ program. 

1.2. The DAQ program uses SubVIs to perform the various tasks 

1.3. Load the LabVIEW program: c:\FC2 Docs\DAQ Program\ FEL Transfer.vi (do one of 

the following) 

1.3.1. From the start menu 

1.3.1.1. Click Start

1.3.1.2. Click FEL Transfer

1.3.2. From Windows Explorer 

1.3.2.1.Locate FEL Transfer.vi and double click to open 

1.3.3. From LabVIEW 

1.3.3.1. Open LabVIEW 

1.3.3.2. Click FEL Transfer.vi

1.4. Run the program (do one of the following) 

1.4.1. Press Ctrl+R

1.4.2. Click the Run icon ► on the tool bar 

1.4.3. Click the menu item Operate then Run

1.5. Enter Lamp Serial Numbers

1.6. Click Start Scan

2. Lamp scan program (Lamp Scan.vi) 

2.1. The lamp scan program scans the dark signal then the full scale signal at each 

wavelength for one spectral range determined by the detector used 

2.2. The lamp scan program does not communicate with the lamp current control program 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 1 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F6 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

2.3. The DAQ program runs the lamp scan program three times to cover the entire 

calibration range. Each run creates one raw data file and formatted data file. The three 

formatted data files are combined into a new file which contains the net signals and 

percent standard deviation of the net signal data for all three ranges. 

2.3.1. Format of raw data file 

2.3.1.1. Filename: F000xmmddyyyya.raw 

2.3.1.2. Wavelength [nm], McPherson absolute encoder reading, date, time 

2.3.1.3. Lamp station, lamp serial number, Heidehain linear encoder reading 

2.3.1.4. Dark signals [V], wavelength [nm], McPherson absolute encoder reading, 

Aerotech Z-axis position [mm], dark signal mean [V], percent standard 

deviation of the dark signal 

2.3.1.5. Station 1 current [A], station 2 current [A], station 3 current [A], station 4 

current [A], station 1 voltage [V], station 2 voltage [V], station 3 voltage [V], 

station 4 voltage [V] 

2.3.1.6. Full scale signals [V], wavelength [nm], McPherson absolute encoder 

reading, Aerotech Z-axis position [mm], full scale signal mean [V], percent 

standard deviation of the full scale signal [%] 

2.3.2. Format of formatted data file 

2.3.2.1. Filename: F000xmmddyyyya.fmt 

2.3.2.2. Wavelength [nm], McPherson absolute encoder reading, date, time, lamp 

station, lamp serial number, Heidehain linear encoder reading, wavelength 

[nm], net signal mean [V], percent standard deviation of the net signal [%] 

2.3.3. Format of combined data file 

2.3.3.1. Filename: F000xmmddyyyya.-F000xmmddyyyyb.F000xmmddyyyyc.-prs 

2.3.3.2. Wavelength [nm], net signal [V], percent standard deviation of the net signal 

[%] 

2.4. The lamp scan program can run alone to measure one spectral range for one lamp 

2.5. The DAQ program sets up the monochromator for each spectral range. Use the 

motion control program to set up the monochromator when using the lamp scan 

program as a stand-alone program. 

2.6. Select the Grating

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 2 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F7 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

2.7. Select the Lamp Station

2.8. Enter the Lamp S/N

2.9. Select the Detector

2.10. Run the program 

3. Motion control program (Motionmenu.vi) 

3.1. Run the motion control program to load the menu options 

3.2. The menu options 

3.2.1. Enable Axis 

3.2.1.1. Detector Stage 

3.2.1.2. Wavelength 

3.2.1.3. Main Table 

3.2.2. Home Axis 

3.2.2.1. Detector Stage 

3.2.2.2. Wavelength 

3.2.2.3. Main Table 

3.2.3. Move Axis 

3.2.3.1. Detector Stage 

3.2.3.1.1. Silicon 

3.2.3.1.2. InGaAs 

3.2.3.1.3. HeNe Laser 

3.2.3.2. Wavelength 

3.2.3.3. Main Table 

3.2.4. Shutter 

3.2.4.1. Lamp 1 

3.2.4.1.1. Open 

3.2.4.1.2. Close 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 3 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F8 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

3.2.4.2. Lamp 2 

3.2.4.2.1. Open 

3.2.4.2.2. Close 

3.2.4.3. Lamp 3 

3.2.4.3.1. Open 

3.2.4.3.2. Close 

3.2.4.4. Lamp 4 

3.2.4.4.1. Open 

3.2.4.4.2. Close 

3.2.4.5. Open All 

3.2.4.6. Close All 

3.2.5. Monochromator 

3.2.5.1. Grating 

3.2.5.1.1. UV-VIS 

3.2.5.1.2. IR 

3.2.5.2. Wavelength 

3.2.5.3. Exit mirrors 

3.2.5.3.1. Single monochromator 

3.2.5.3.2. Double monochromator 

3.2.5.3.2.1. PMT 

3.2.5.3.2.2. Si, InGaAs, HeNe 

3.2.5.4. Filter wheel 

3.2.5.4.1. 1 

3.2.5.4.2. 2 

3.2.5.4.3. 3 

3.2.5.4.4. 4 

3.2.5.4.5. 5 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 4 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F9 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

3.2.5.4.6. 6 

4. Lamp stability program (FEL Stability.vi) 

4.1. The lamp stability program measures selected lamps periodically (usually once an hour 

over a 22 hour period) 

4.2. This program communicates with the lamp current control program and starts the 

stability measurements after the lamps have operated for 20 minutes 

4.3. This program does not ramp down the lamps at the end of the measurement 

4.4. Run program 

4.5. Select Lamps to be Measured

4.6. Click Press to Run

4.7. Enter filename 

5. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 29-Jun-06 C. Gibson 12 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 5 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F10 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

Figure Irr1.1. Front panel of FEL Transfer.vi

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 6 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F11 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

Figure Irr1.2. Front panel of Lamp Scan.vi

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 7 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F12 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

Figure Irr1.3. Sample raw data from lamp scan program 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 8 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F13 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

Figure Irr1.4. Sample formatted data from lamp scan program 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 9 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F14 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

Figure Irr1.5. Sample combined formatted data from DAQ program. The three 

formatted data files from the lamp scan program are combined into a single file. 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 10 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F15 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

Figure Irr1.6. Front panel of MotionMenu.vi

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 11 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F16 

Irradiance Calibration Procedure 

IRR-CP-IRR1-FASCAL2 Data Acquisition Program Operation

Figure Irr1.7. Front panel of FEL Stability.vi

Procedure Version Date Author Pages Filename 

IRR-CP-IRR1 1.0 29-Jun-06 C. Gibson 12 of 12 IRR-CP-IRR1 FC2 DAQ 

Program Operation v1.doc 
F17 

Irradiance Calibration Procedure 

IRR-CP-IRR2-Quartz Halogen Lamp Alignment

Quartz Halogen Lamp (QHL) Alignment

BRIGHT SOURCE 

BURN 

COLLISION 

ELECTROCUTION

1. The spectral irradiance is measured at 50 cm from the receiving aperture of the 

spectroradiometer to the front surface of the lamp bi-posts. 

2. The lamp is operated in a kinematic lamp socket. 

3. Lamp alignment overview 

3.1. The lamp is measured at a distance of 50 cm from the entrance aperture of the 

integrating sphere with an aperture area of 1.0027 cm2

. The sphere views approximately 

a 9 cm diameter target in the plane of the front surface of the lamp bi-posts. With this 

geometry, the entire lamp is viewed from the top of the lamp envelope down to the top 

half of the black lamp base. Light baffling is used between the lamp and the 

spectroradiometer integrating sphere to minimize effects of scattered light. 

3.2. The lamp is mounted vertically, base down with the brass identification plate facing 

away from the spectroradiometer. The lamp serial number and electrical polarity are 

indicated on the plate. An alignment jig is placed in the kinematic lamp socket and 

aligned. This is accomplished by placing a spirit level on top of the jig and then by 

adjusting the angle about the optical axis until the level is balanced. The alignment jig 

target area, which is indicated by cross hairs, is centered between the bi-posts and 

located 9.5 cm above the bottom of the jig bi-posts. This target area is centered 

vertically and horizontally onto the optical axis. The jig is set perpendicular to the 

optical axis by reflecting the spectroradiometer laser beam back onto itself. The 

distance along the optical axis from the target area surface to the surface of the sphere 

aperture is set at 50 cm. The target area surface is in the plane with the front surface of 

the bi-posts. This alignment procedure sets the alignment jig bi-posts relative to the 

optical axis of the spectroradiometer. The jig is removed and the lamp is placed in the 

aligned socket. 

4. Run the motion control (see IRR-CP-IRR1) 

5. Align the integrating sphere 

5.1. Put a dummy lamp in lamp station 4 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR2 1.0 27-Jun-06 C. Gibson 1 of 4 IRR-CP-IRR2 Quartz Halogen 

Lamp Alignment v1.doc 
F18 

Irradiance Calibration Procedure 

IRR-CP-IRR2-Quartz Halogen Lamp Alignment

5.2. Turn on the lamp 

5.3. Move the main table to lamp station 4 

5.4. Use the scope to view the image of the integrating sphere exit port on the 

monochromator slit 

5.5. Adjust the spherical mirror to center the image of the integrating sphere exit port on the 

monochromator slit 

6. Align the lamp sockets 

6.1. Use the motion control program to position the internal laser (see IRR-CP-IRR1) 

6.2. Set grating to UV-VIS (grating #1) 

6.3. Set exit mirror to double monochromator (Si, InGaAs, HeNe setting) 

6.4. Set filter wheel to position 6 

6.5. Set wavelength to 632.8 

6.6. Turn on internal laser 

6.7. Check that laser illuminates the sphere (this verifies the spectroradiometer settings) 

6.8. Turn off internal laser 

6.9. Put alignment jig in lamp station 1 

6.10. Move the main table to lamp station 1 

6.11. Turn on external laser 

6.12. Install beam splitter 

6.13. Align external laser on the center of the integrating sphere (IS) aperture 

6.14. Move the main table to lamp station 0 

6.15. Remove integrating sphere 

6.16. Put in mirror 

6.17. Turn on internal laser 

6.18. Move the main table to lamp station 1 

6.19. Align internal laser onto external laser by adjusting the mirror 

6.20. Align alignment jig using the internal laser 

6.21. Remove mirror 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR2 1.0 27-Jun-06 C. Gibson 2 of 4 IRR-CP-IRR2 Quartz Halogen 

Lamp Alignment v1.doc 
F19 

Irradiance Calibration Procedure 

IRR-CP-IRR2-Quartz Halogen Lamp Alignment

6.22. Put in integrating sphere 

6.23. Use the distance gauge to measure 50 cm from the aperture of the integrating sphere to 

the front surface of the alignment jig 

7. Repeat alignment for lamp stations 2 thru 4 

8. Insert the lamp(s) in the lamp socket(s) 

8.1. Do not touch lamp envelope 

8.2. Place lamp in the socket 

8.2.1. Check lamp polarity 

8.2.1.1. Polarity is indicated on the brass plate 

8.2.2. Set brass plate with lamp serial number away from the spectroradiometer 

8.2.3. Use your left hand to place the lamp in the socket 

8.2.4. Hold the left post lightly against the socket terminal 

8.2.5. Turn the left socket knob counterclockwise to fasten the lamp 

8.2.6. Turn the right socket knob counterclockwise to fasten the lamp 

9. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 27-Jun-06 C. Gibson 4 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR2 1.0 27-Jun-06 C. Gibson 3 of 4 IRR-CP-IRR2 Quartz Halogen 

Lamp Alignment v1.doc 
F20 

Irradiance Calibration Procedure 

IRR-CP-IRR2-Quartz Halogen Lamp Alignment

 Figure Irr2. This drawing shows the target area viewed by 

the spectroradiometer integrating sphere. 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR2 1.0 27-Jun-06 C. Gibson 4 of 4 IRR-CP-IRR2 Quartz Halogen 

Lamp Alignment v1.doc 

9 cm

View half way down base 

Baffle

Integrating sphere 

Lamp 
F21 

Irradiance Calibration Procedure 

IRR-CP-IRR3-Quartz Halogen Lamp Operation

Quartz Halogen Lamp (QHL) Operation 

BRIGHT SOURCE 

BURN 

COLLISION 

ELECTROCUTION

1. Operating conditions 

1.1. The lamp is slowly ramped up to 8.2 A DC over 5 minutes. 

1.2. The lamp current is maintained at (8.2000 ± 0.0002) A during the calibration. 

1.3. Measurements are started after the lamp has stabilized for 20 min. 

2. Align the lamp sockets (See IRR-CP-IRR2) 

3. Do not touch lamp envelope 

4. Place lamp(s) in the lamp socket(s) 

5. Turn on the digital multimeter (DMM) 

6. Turn on the digital-to-analog converter (D/A converter) 

7. Check that the correct lamp power cable is connected to the power supply 

8. Turn on all four power supplies 

9. Load the lamp current control program (Lamp Current Control.vi) 

9.1. The lamp current control program ramps up, regulates, and ramps down the lamp 

currents. The serial number, date, time, lamp current, lamp voltage, and burning time 

are stored in a summary file. The serial number, date, lamp current, lamp voltage, and 

total burning time are stored in a lamp time file. 

9.2. Turn on the computer 

9.3. Load the LabVIEW program: c:\FC2 PS Docs\Lamp Control Program\ Lamp Current 

Control.vi (do one of the following) 

9.3.1. From the start menu 

9.3.1.1. Click Start

9.3.1.2. Click Lamp Current Control

Procedure Version Date Author Pages Filename 

IRR-CP-IRR3 1.0 27-Jun-06 C. Gibson 1 of 6 IRR-CP-IRR3 Quartz Halogen 

Lamp Operation v1.doc 
F22 

Irradiance Calibration Procedure 

IRR-CP-IRR3-Quartz Halogen Lamp Operation

9.3.2. From Windows Explorer 

9.3.2.1.Locate Lamp Current Control.vi and double click to open 

9.3.3. From LabVIEW 

9.3.3.1.Open LabVIEW 

9.3.3.2. Click Lamp Current Control.vi

9.4. Enter Lamp serial number 

9.5. Enter Lamp Current [A]

9.6. Click the Enable button for the lamp(s) to ramp up 

9.6.1. The power output to the unselected lamps is disabled 

9.7. If also running the DAQ program (FEL Transfer.vi) (See IRR-CP-IRR1), enable only 

the first lamp. The DAQ program communicates with the Lamp Current Control 

program to ramp up the lamp, wait 20 minutes for the lamp to stabilize, measure the 

lamp and then ramp down the lamp. Measurements are performed for the lamps 

entered into the DAQ program. 

10. Run the program (do one of the following) 

10.1. Press Ctrl+R

10.2. Click the Run icon ► on the tool bar 

10.3. Click the menu item Operate then Run

11. Enter the lamp data filename (psdatayyyymmdd.txt) 

12. Turn off lamps 

12.1. Enter Lamp Current [A] (value = 0)

12.2. Click the Enable button for the lamp(s) to ramp down 

13. MANUAL TURN OFF

13.1. Go to the supply 

13.2. Press the LCL button to set the power supply to the local mode 

13.3. Press the Output Adjust button and toggle to Voltage

13.4. Press and hold the Display setting button 

13.5. Turn the Output Adjust knob counterclockwise until the display reads 0.00 volts

13.6. Turn off the supply 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR3 1.0 27-Jun-06 C. Gibson 2 of 6 IRR-CP-IRR3 Quartz Halogen 

Lamp Operation v1.doc 
F23 

Irradiance Calibration Procedure 

IRR-CP-IRR3-Quartz Halogen Lamp Operation

14. MANUAL RESET AFTER ERROR

14.1. Reset power supply if Yellow LED is lit 

14.2. Turn off the power supply 

14.3. Turn on the power supply 

14.4. Press the Output Adjust button and toggle to Voltage

14.5. Press and hold the Display setting button 

14.6. Set the voltage limit by turning the Output Adjust knob clockwise until the 

display reads the target voltage limit (122.0 volts)

14.7. The constant current (CC) indicator light should now be lit 

15. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 27-Jun-06 C. Gibson 6 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR3 1.0 27-Jun-06 C. Gibson 3 of 6 IRR-CP-IRR3 Quartz Halogen 

Lamp Operation v1.doc 
F24 

Irradiance Calibration Procedure 

IRR-CP-IRR3-Quartz Halogen Lamp Operation

Figure Irr3.1. Front panel of Lamp Current Control.vi 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR3 1.0 27-Jun-06 C. Gibson 4 of 6 IRR-CP-IRR3 Quartz Halogen 

Lamp Operation v1.doc 
F25 

Irradiance Calibration Procedure 

IRR-CP-IRR3-Quartz Halogen Lamp Operation

Figure Irr3.2. Sample lamp summary file 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR3 1.0 27-Jun-06 C. Gibson 5 of 6 IRR-CP-IRR3 Quartz Halogen 

Lamp Operation v1.doc 
F26 

Irradiance Calibration Procedure 

IRR-CP-IRR3-Quartz Halogen Lamp Operation

Figure Irr3.3. Sample lamp time file 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR3 1.0 27-Jun-06 C. Gibson 6 of 6 IRR-CP-IRR3 Quartz Halogen 

Lamp Operation v1.doc 
F27 

Irradiance Calibration Procedure 

IRR-CP-IRR4-High Temperature Blackbody (HTBB) Alignment

High Temperature Blackbody (HTBB) Alignment

BRIGHT SOURCE 

BURN 

COLLISION 

ELECTROCUTION

1. Run the motion control program (see IRR-CP-IRR1) 

2. Align the integrating sphere (IS) 

2.1. Put a dummy lamp in lamp station 4 

2.2. Turn on the lamp 

2.3. Move the main table to lamp station 4 

2.4. Use the scope to view the image of the integrating sphere exit port on the 

monochromator slit 

2.5. Adjust the spherical mirror to center the image of the integrating sphere exit port on the 

monochromator slit 

2.6. Turn off the lamp 

3. Define the HTBB optical axis 

3.1. Move the main table to lamp station 5 

3.2. Position the HTBB window approximately 50 cm from the IS aperture 

3.3. Level the HTBB housing 

3.4. Install a beam splitter (microscope slide cover) between the HTBB and the IS 

3.5. Install an external laser perpendicular to the optical axis 

3.6. Turn on the external laser 

3.7. Center the HTBB on the laser 

3.8. Adjust the HTBB until the laser goes through the center of the HTBB window and the 

center of the cavity bottom 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR4 1.0 20-Sep-06 C. Gibson 1 of 3 IRR-CP-IRR4 HTBB Alignment 

v1.doc 
F28 

Irradiance Calibration Procedure 

IRR-CP-IRR4-High Temperature Blackbody (HTBB) Alignment

4. Align the water-cooled aperture (WCA) 

4.1. Use double stick tape to attach a microscope slide to the HTBB water-cooled aperture 

4.2. Position the WCA approximately 45 cm from the IS aperture 

4.3. Center the WCA on the optical axis 

4.4. Adjust the WCA until it is centered on the laser and normal to it 

5. Align the HTBB 

5.1. Use double stick tape to attach a microscope slide to the IS aperture mount 

5.2. Align the external laser on the center of the integrating sphere (IS) aperture 

5.2.1. Do not make any adjustments to the IS 

5.2.2. Translate the main table to translate the IS in the horizontal axis 

5.3. Adjust the laser and/or the beam splitter until the laser is centered on the IS aperture and 

normal to it 

6. Repeat sections 3 and 4 to realign the HTBB and WCA on the optical axis defined by the IS 

7. Remove the beam splitter (microscope slide cover) 

8. Remove the microscope slides from the apertures 

9. Measure the distance between the WCA and the IS 

10. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 20-Sep-06 C. Gibson 3 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR4 1.0 20-Sep-06 C. Gibson 2 of 3 IRR-CP-IRR4 HTBB Alignment 

v1.doc 
F29 

Irradiance Calibration Procedure 

IRR-CP-IRR4-High Temperature Blackbody (HTBB) Alignment

 Figure Irr4. This drawing shows the optical layout for the HTBB alignment 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR4 1.0 20-Sep-06 C. Gibson 3 of 3 IRR-CP-IRR4 HTBB Alignment 

v1.doc 

Laser 

High temperature blackbody 

Integrating sphere 

Beam splitter 

Precision aperture 
F30 

Irradiance Calibration Procedure 

IRR-CP-IRR5-High Temperature Blackbody (HTBB) Operation

High Temperature Blackbody (HTBB) Operation

BRIGHT SOURCE 

BURN 

COLLISION 

ELECTROCUTION

1. HTBB Preparation 

1.1. Turn on the argon supply (set flow rate to 0.5 L/min (11 on the flow meter)) 

1.2. Close the argon needle valve on the rear of the HTBB 

1.3. Turn on cold water to HTBB furnace (20 psi) 

1.4. Turn on chilled water (55 oF) to power supply (20 psi) 

1.5. Turn on cold water to the water-cooled aperture 

1.6. Purge the HTBB 

1.6.1. Install the vacuum plate and window cap on the front of the HTBB 

1.6.2. Check the vacuum fitting 

1.6.3. Connect the vacuum hose 

1.6.4. Open the valve to the vacuum pump 

1.6.5. Pump down the HTBB with the rough vacuum pump until the pressure reaches 

-100 kPa 

1.6.6. Close valve to vacuum pump 

1.6.7. Turn off vacuum pump 

1.6.8. Open the HTBB argon needle valve to the FULL position 

1.6.9. Close the HTBB argon needle valve when the pressure reaches 20 kPa 

1.6.10. Repeat the purging sequence two more times 

2. Turn On Procedure 

2.1. Remove the vacuum plate and window cap from the front of HTBB 

2.2. Turn on the main circuit breaker 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR5 1.0 22-Sep-06 C. Gibson 1 of 6 IRR-CP-IRR5 HTBB Operation 

v1.doc 
F31 

Irradiance Calibration Procedure 

IRR-CP-IRR5-High Temperature Blackbody (HTBB) Operation

2.3. Power supply specifications 

2.3.1. Input: 480 VAC, 3 Phase, 4 wire, Wye, 60 Hz, 27 kVA 

2.3.2. Output: 600 A at 30 VDC 

2.3.3. Current regulation: 0.0005% of maximum 

2.3.4. Voltage ripple: 55 mV peak to peak into resistive load 

2.3.5. Cooling: 5 GPM water at 50 PSID nominally 

2.3.6. Physical: 60” high x 23.25” wide x 28.25” deep 

2.3.7. Weight: 900 lbs 

2.4. Turn power supply switch clockwise to the ON position (1) 

2.5. Press the Start button on the power supply keypad 

2.6. The Red LED is lit indicating that the power supply is ON

3. Operating Procedure 

3.1. Load the Digital Multimeter Feedback Program: c:\FC2 HTBB 

Docs\HTBB\22_hp3457_feedback.vi

3.2. Note: The Digital Multimeter Feedback Program stores the HTBB detector signal in a 

global variable that is read by the HTBB Control Program 

3.2.1. Enter the GPIB address 

3.2.2. Enter the channel 

3.2.3. Enter the NPLC 

3.2.4. Select Function 

3.2.4.1. Initialize device 

3.2.4.2. Measurement 

3.2.4.3. Release device 

3.2.5. Run the Digital Multimeter Feedback Program 

3.3. Load the HTBB Control Program: c:\FC2 HTBB Docs\HTBB\BB3200_(main.exe).vi

Procedure Version Date Author Pages Filename 

IRR-CP-IRR5 1.0 22-Sep-06 C. Gibson 2 of 6 IRR-CP-IRR5 HTBB Operation 

v1.doc 
F32 

Irradiance Calibration Procedure 

IRR-CP-IRR5-High Temperature Blackbody (HTBB) Operation

3.4. The HTBB control program starts in the current control mode and ramps the HTBB from 

room temperature to 1700 oC by ramping the current which corresponds to a nominal 

temperature. After the temperature set point is reached, the operator starts the PID 

control mode. In the PID mode, the program uses a moving set point to increase the 

temperature to approximately 2677 oC. When the final temperature set point is achieved, 

the program maintains the set point for the duration of the measurements. At end of the 

measurements, the operator starts the current control mode and the program ramps the 

current to 0 A. 

3.5. Ramp current from zero (Current Control Mode) 

3.5.1. Click the power supply on button (green) 

3.5.2. Enter the current slew rate A/sec: 0.1 

3.5.3. Enter the target temperature, oC 

3.5.4. Enter the moving set temperature (enter the same value as the target temperature) 

3.5.5. Click the PID button off (red) 

3.5.6. Enter the Output filename 

3.5.7. Run the HTBB control program 

3.6. Ramp temperature to the final set point and monitor set point (PID Control Mode) 

3.6.1. Enter the temperature rate, oC/s (usually 1 to 3 oC per second) 

3.6.2. Enter upper limit 

3.6.3. Enter lower limit 

3.6.4. Click the PID button on (green) 

3.6.5. Enter new moving set temperature, oC 

4. Turn Off Procedure (Current Control Mode) 

4.1. Enter current slew rate A/sec: 0.1 

4.2. Click the PID button off (red) 

4.3. Enter zero (0) for the Target Temperature, oC 

4.4. Power supply will ramp down HTBB over 2 hours 

4.5. Turn power supply switch counter clockwise to the OFF position (0) 

4.6. Turn off the main circuit breaker 

4.7. Turn off cold water to the HTBB furnace 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR5 1.0 22-Sep-06 C. Gibson 3 of 6 IRR-CP-IRR5 HTBB Operation 

v1.doc 
F33 

Irradiance Calibration Procedure 

IRR-CP-IRR5-High Temperature Blackbody (HTBB) Operation

4.8. Turn off cold water to the HTBB aperture 

4.9. Turn off chilled water to the power supply 

4.10. Install vacuum plate and cap on front of HTBB 

4.11. Turn off argon 

5. Document History 

Version Version 

Date Author Page Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 22-Sep-06 C. Gibson 6 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR5 1.0 22-Sep-06 C. Gibson 4 of 6 IRR-CP-IRR5 HTBB Operation 

v1.doc 
F34 

Irradiance Calibration Procedure 

IRR-CP-IRR5-High Temperature Blackbody (HTBB) Operation

Figure Irr5.1. Front panel of the Digital Multimeter Feedback Program 

(22_hp3457_feedback.vi) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR5 1.0 22-Sep-06 C. Gibson 5 of 6 IRR-CP-IRR5 HTBB Operation 

v1.doc 
F35 

Irradiance Calibration Procedure 

IRR-CP-IRR5-High Temperature Blackbody (HTBB) Operation

Figure Irr5.2. Front panel of the HTBB Control Program (BB3200_(main.exe).vi) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR5 1.0 22-Sep-06 C. Gibson 6 of 6 IRR-CP-IRR5 HTBB Operation 

v1.doc 
F36 

Irradiance Calibration Procedure 

IRR-CP-IRR6-Filter Radiometer (FR) Alignment

Filter Radiometer (FR) Alignment

BRIGHT SOURCE 

BURN 

COLLISION 

ELECTROCUTION

1. Run the motion control program (see IRR-CP-IRR1) 

2. Align the high temperature blackbody (HTBB) (see IRR-CP-IRR4) 

3. Use double stick tape to attach a microscope slide to the HTBB water-cooled aperture 

4. Use double stick tape to attach a microscope slide to the FR aperture mount 

5. Align the filter radiometer (FR) 

5.1. Move the FR to the HTBB position 

5.2. Align the FR on the HTBB optical axis 

5.3. Adjust the FR until the FR aperture is centered on the laser and normal to it 

6. Repeat align for all filter radiometers 

7. Remove the beam splitter (microscope slide cover) 

8. Remove the microscope slides from the apertures 

9. Measure the distance between the HTBB water-cooled aperture and the FR 

10. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 20-Sep-06 C. Gibson 2 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR6 1.0 20-Sep-06 C. Gibson 1 of 2 IRR-CP-IRR6 FR Alignment 

v1.doc 
F37 

Irradiance Calibration Procedure 

IRR-CP-IRR6-Filter Radiometer (FR) Alignment

 Figure Irr6. This drawing shows the optical layout for the HTBB and FR alignment 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR6 1.0 20-Sep-06 C. Gibson 2 of 2 IRR-CP-IRR6 FR Alignment 

v1.doc 

Laser 

High temperature blackbody 

Filter radiometer 

Beam splitter 

Precision aperture 
F38 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Spectral Irradiance Scale Realization

BRIGHT SOURCE 

BURN 

COLLISION 

ELECTROCUTION

1. Run the motion control program (see IRR-CP-IRR1) 

2. Align the quartz halogen lamp(s) (QHL) (see IRR-CP-IRR2) 

3. Align the high temperature blackbody (HTBB) (see IRR-CP-IRR4) 

4. Align the filter radiometer(s) (FR) (see IRR-CP-IRR6) 

5. Turn on the HTBB (See IRR-CP-IRR5) 

6. Measure the temperature of the HTBB using the FRs 

6.1. Load the Visual Basic program: c:\FASCAL Docs\DataAcQ\FASCAL.vbp

6.2. Run the program 

6.3. Load the Filter radiometer measurements program (Frmeas.frm) 

6.3.1. Click HTBB vs. FRs from the Hardware.frm menu 

6.3.2. Enter the filter radiometer setup data 

6.3.2.1. Select the Use button(s) 

6.3.2.2. Enter the filter radiometer name(s) 

6.3.2.3. Enter the station (position in steps) 

6.3.2.4. Enter the digital multimeter channel 

6.3.3. Click the Set Pos. button to move the selected FR to the HTBB 

6.3.4. Click the Read Pos. button to read the current position of the selected FR and store 

the value in the station text box 

6.3.5. Select measurement mode (do one of the following) 

6.3.5.1. Measure N times 

6.3.5.1.1. Enter value in text box for N (typically N = 5) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 1 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F39 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

6.3.5.2. Measure once 

6.3.6. Click the Save config. button 

6.3.7. Enter the 3457A digital multimeter data 

6.3.7.1. Click the Read Once or Read button to read a FR signal 

6.4. Measure the full scale signal 

6.4.1. Click the Measure FRs button 

6.5. Put the rod shutter in front of the HTBB 

6.6. Measure the dark signal 

6.6.1. Click the Measure FRs button 

6.7. Calculate the net signals (do one of the following) 

6.7.1. Load the Visual Basic program: c:\FC Docs\Ereal\Ereal.vbp and run it 

6.7.1.1. Click Calc FR net signals from the FRTCalc.frm menu to load the FR net 

signal calculation program (FRSigCalc.frm)

6.7.1.2. Enter the input filename 

6.7.1.3. Enter the output filename 

6.7.1.4. Enter the number of groups of full scale signals 

6.7.1.5. Enter the number of full scale signals per group 

6.7.1.6. Enter the number of dark signals per group 

6.7.1.7. Click the Reduce FR file button 

6.7.2. Open the measurement data file for each filter radiometer in a spreadsheet and 

calculate the net signals 

7. Measure the spectral irradiance of the HTBB using the spectroradiometer (see IRR-CP-IRR1) 

8. Measure the spectral irradiance of the QHL(s) (see IRR-CP-IRR8) 

9. Measure the temperature of the HTBB using the FRs (repeat section 6) 

10. Calculate the HTBB temperature from the FR measurements 

10.1. Load the Visual Basic program: c:\FC Docs\Ereal\Ereal.vbp and run it 

10.2. The Calculate HTBB temperature and irradiance program (FRTCalc.frm) is loaded 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 2 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F40 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

10.3. Step 1: Load the FR parameter file 

10.3.1. Select the FR button 

10.3.2. Click the Load FR values button 

10.4. Step 2: Calculate the HTBB temperature 

10.4.1. Enter the FR measurement date 

10.4.2. Enter the FR net signal 

10.4.3. The other parameters are loaded in Step 1 

10.4.3.1. The white boxes are used for data entry 

10.4.3.2. The gray boxes display calculated values 

10.4.4. Click the Calculate BB Temperature button 

11. Calculate the HTBB spectral irradiance from the FR measurements 

11.1. Perform steps in Section 10 

11.2. Step 3: Calculate the HTBB spectral irradiance 

11.2.1. Enter the temperature [K] 

11.2.1.1. The HTBB temperature is determined for each FR. Use the average of the 

group of temperature determinations. If the temperature is measured before 

and after the spectral irradiance measurements then there will be two 

temperature averages. 

11.2.2. Select the spectral range (do one of the following) 

11.2.2.1. Click the Calibration service 250 nm to 2400 nm button 

11.2.2.2. Click the CCPR 250 nm to 2500 nm button 

11.2.2.3. Click the Other button 

11.2.3. Enter the output filename 

11.2.4. Enter the integrating sphere aperture (ISR) to HTBB aperture distance [cm] 

11.2.5. Enter the integrating sphere aperture (ISR) diameter [cm] 

11.2.6. Click the Calculate Irradiance button 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 3 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F41 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

12. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 20-Sep-06 C. Gibson 11 

 

 

 

 

Figure Irr7.1. Front panel of the filter radiometer measurement program (Frmeas.frm) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 4 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F42 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Figure Irr7.2. Sample measurement data for Filter Radiometer #2 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 5 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F43 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Figure Irr7.3. Front panel of the calculate FR net signals program (FRSigCalc.frm) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 6 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F44 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Figure Irr7.4. Front panel of the calculate HTBB temperature and irradiance program 

(FRTCalc.frm) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 7 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F45 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Figure Irr7.5. Sample FR parameter file used by the calculate HTBB temperature and 

irradiance program (FRTCalc.frm) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 8 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F46 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Figure Irr7.6. Sample power responsivity data for Filter Radiometer #2 used by the calculate 

HTBB temperature and irradiance program (FRTCalc.frm) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 9 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F47 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Figure Irr7.7. Sample temperature data Filter Radiometers #2, #3, and #4 which is the output 

from the calculate HTBB temperature and irradiance program (FRTCalc.frm) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 10 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F48 

Irradiance Calibration Procedure 

IRR-CP-IRR7-Spectral Irradiance Scale Realization

Figure Irr7.8. Sample HTBB spectral irradiance data calculated from calculate HTBB 

temperature and irradiance program (FRTCalc.frm) 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR7 1.0 20-Sep-06 C. Gibson 11 of 11 

IRR-CP-IRR7 Spectral 

Irradiance Scale Realization 

v1.doc 
F49 

Irradiance Calibration Procedure 

IRR-CP-IRR8-Spectral Irradiance Calibration

Spectral Irradiance Calibration

BRIGHT SOURCE 

BURN 

COLLISION 

ELECTROCUTION

1. Align the lamps (See IRR-CP-IRR2) 

2. Run the Lamp Current Control Program (see IRR-CP-IRR3) 

3. Run the FASCAL2 Data Acquisition Program (see IRR-CP-IRR1) 

4. Reduce the calibration data (see IRR-CP-IRR9) 

5. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 27-Jun-06 C. Gibson 1 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR8 1.0 27-Jun-06 C. Gibson 1 of 1 IRR-CP-IRR8 Spectral 

Irradiance Calibration v1.doc 
F50 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Spectral Irradiance Data Reduction

1. Calculate the calibration factor (CF) 

1.1. Open the primary working standards (PWS) irradiance spreadsheet: c:\FC2 Docs\Irrad 

PWS\PWS irradiances 1003.xls

1.2. Open the calibration factor spreadsheet: c:\FC2 Docs\Irrad PWS\CalFactor 

mmddyy.xls

1.3. Save CF spreadsheet with new name 

1.4. Edit CF spreadsheet 

1.4.1. Enter new spreadsheet name 

1.4.2. Enter current date 

1.4.3. Enter PWS serial numbers 

1.4.4. Edit chart titles 

1.4.5. Save spreadsheet 

1.5. Edit irradiance values in the CF spreadsheet 

1.5.1. Copy irradiances from the PWS irradiance spreadsheet 

1.5.2. Save CF spreadsheet 

1.6. Open PWS signal files in Excel 

1.6.1. Plot data 

1.6.2. Review, don’t save 

1.7. Edit signal values in the CF spreadsheet 

1.7.1. Copy PWS signal values from the PWS signal files 

1.7.2. Save CF spreadsheet 

1.8. Print CF spreadsheet 

2. Calculate the irradiance of test lamp 

2.1. Open the test irradiance spreadsheet: c:\FC2 Docs\Irrad PWS\F000 mmddyy cal.xls

2.2. Save test irradiance spreadsheet with new name 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 1 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F51 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

2.3. Edit test irradiance spreadsheet 

2.3.1. Enter new spreadsheet name 

2.3.2. Enter current date 

2.3.3. Edit chart titles 

2.3.4. Copy Mean CF from the CF spreadsheet 

2.3.5. Edit CF date 

2.3.6. Save spreadsheet 

2.4. Open test signal files in Excel 

2.4.1. Plot data 

2.4.2. Review, don’t save 

2.5. Edit signal values in the test signal spreadsheet 

2.5.1. Copy test signal values from the test signal files 

2.5.2. Save test irradiance spreadsheet 

2.6. Prepare data for calibration report 

2.6.1. Copy test irradiance from the Data reduction worksheet to the Final data 

worksheet 

2.6.2. Edit lamp current and lamp voltage 

2.7. Print test irradiance spreadsheet 

3. Document History 

Version Version 

Date Author Page Total 

Revision 

Date 

Revision 

Date 

Revision 

Date 

Revision 

Date 

1.0 28-Jun-06 C. Gibson 9 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 2 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F52 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Figure Irr9.1. Primary working standard spreadsheet with spectral irradiance values 

in W cm-3. The wavelength is in nm. 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 3 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F53 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Figure Irr9.2. Sample signal file. The first column is wavelength in nm. The second column is 

the net signal in V. The last column is the percent standard deviation of the net signal. 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 4 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F54 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Figure Irr9.3. Left side of sample calibration spreadsheet 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 5 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F55 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Figure Irr9.4. Right side of sample calibration spreadsheet 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 6 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F56 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Figure Irr9.5. Left side of sample test irradiance spreadsheet 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 7 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F57 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Figure Irr9.6. Right side of sample test irradiance spreadsheet 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 8 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F58 

Irradiance Calibration Procedure 

IRR-CP-IRR9-Spectral Irradiance Data Reduction

Figure Irr9.7. Final data worksheet of sample test irradiance spreadsheet 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR9 1.0 28-Jun-06 C. Gibson 9 of 9 

IRR-CP-IRR9 Spectral 

Irradiance Data Reduction 

v1.doc 
F59 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

Calculate the Correlated Color Temperature (CCT) and Luminous Intensity (LI) from 

Spectral Irradiance Data

1. Fit data to determine the spectral irradiance value at a 10 nm interval 

1.1. Load the Visual Basic program: c:\FC2 Docs\fitdata\Fitirrad.vbp (do one of the 

following) 

1.1.1. From the start menu 

1.1.1.1. Click Start then Data Interpolation shortcut 

1.1.2. From Windows Explorer 

1.1.2.1. Locate Fitirrad.vbp and double click to open 

1.2. Run the program (do one of the following) 

1.2.1. Press F5

1.2.2. Click the Start icon ► on the tool bar 

1.2.3. Click on the menu item Run then on Start

1.3. Blackbody fit program (Part 1 Calculate fit coefficients) (Fitdata.frm)

1.3.1. Click Calculate fit coefficients from the menu 

1.3.1.1. Enter fit parameters 

1.3.1.1.1. Enter the Wavelength (min) [nm]

1.3.1.1.2. Enter the Wavelength (max) [nm]

1.3.1.1.3. Enter the Degrees of freedom

1.3.1.2. Select file to reduce 

1.3.1.2.1. Enter Input File

1.3.1.2.2. Select Input file format 

1.3.1.2.2.1. Option 1: Input file begins with Data

1.3.1.2.2.2. Option 2: Input file begins with a title line and a unit line

1.3.1.3. Click the Calculate fit coefficients button 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 1 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F60 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

1.4. Blackbody fit program (Part 2 Compute irradiance) (Calcirr.frm)

1.4.1. Click Calculate spectral irradiance from blackbody fit from the menu 

1.4.1.1. Enter fit parameters 

1.4.1.1.1. Enter the Wavelength (min) [nm]

1.4.1.1.2. Enter the Wavelength (max) [nm]

1.4.1.1.3. Enter the Increment [nm]

1.4.1.2. Select file to reduce 

1.4.1.2.1. Enter Input File

1.4.1.3.Click the Compute irradiance button 

2. Calculate the photometric units 

2.1. Load the Visual Basic program: c:\FC2 Docs\photmet\Photomet.vbp (do one of the 

following) 

2.1.1. From the start menu 

2.1.1.1. Click Start then Calculate CCT shortcut 

2.1.2. From Windows Explorer 

2.1.2.1. Locate Photmet.vbp and double click to open 

2.2. Run the program (do one of the following) 

2.2.1. Press F5

2.2.2. Click the Start icon ► on the tool bar 

2.2.3. Click on the menu item Run then on Start

2.3. Photometric unit calculation program is loaded (Photomet.frm)

2.4. Enter lamp information 

2.4.1. Enter Lamp name

2.4.2. Enter Current [A]

2.4.3. Enter Voltage [V]

2.4.4. Enter Distance [m]

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 2 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F61 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

2.5. Select file to reduce 

2.5.1. Enter Input File

2.5.1.1. Select Input file format 

2.5.1.1.1. Option 1: Input file begins with Data

2.5.1.1.2. Option 2: Input file begins with a title line and a unit line

2.6. Click the Compute Color Temperature button 

3. Document History 

Version Version 

Date Author Page 

Total 

Revision 

Date 

Revision 

Date 

Revision 

Date 

Revision 

Date 

1.0 29-Jun-06 C. Gibson 9 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 3 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F62 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

Figure Irr10.1. Front panel of Fitdata.frm

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 4 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F63 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

Figure Irr10.2. Front panel of Calcirr.frm

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 5 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F64 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

Figure Irr10.3. Sample fit coefficients from data interpolation program 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 6 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F65 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

Figure Irr10.4. Sample spectral irradiance data from blackbody fit 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 7 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F66 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

Figure Irr10.5. Front panel of Photomet.frm

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 8 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F67 

Irradiance Calibration Procedure 

IRR-CP-IRR10-Calculate the Correlated Color Temperature (CCT) and 

Luminous Intensity (LI) from Spectral Irradiance Data

Figure Irr10.6. Sample correlated color temperature and luminous intensity data 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR10 1.0 29-Jun-06 C. Gibson 9 of 9 IRR-CP-IRR10 CCT and LI from 

Irradiance v1.doc 
F68 

Irradiance Calibration Procedure 

IRR-CP-IRR11-Reset Linear Encoder

Reset Linear Encoder

1. The Linear Encoder requires resetting when the Reference Mark is lost. 

2. When the HEIDENHAIN display unit is powered on, the blinking REF indicator shows that 

the display is waiting for reference mark traversing 

3. Press the ENT (Enter) key 

4. The display shows 14.000.0 with blinking decimal points 

5. Use the Unidex 511 motion controller to move the boxcar to the reference mark 

6. If the Red LED above the controller is lit then toggle the switch next to the LED to reconnect 

AC power to the unit. The LED is off during normal operation. 

7. Turn on the controller 

8. Press F5 (MDI) on the keypad or keyboard 

9. Press F2 (JOG) on the keypad or keyboard 

10. Use the keypad or keyboard arrows (up/down) to select axis U

11. Press F3 (ENABLE) on the keypad or the keyboard 

12. Press F1 (HIGH SPEED) on the keypad or the keyboard 

13. Use the keypad or keyboard arrows (left/right) to move the boxcar to the reference 

position

14. After traversing the reference mark, the HEIDENHAIN display shows the measured value 

with non-blinking decimal points and non-blinking REF indicator 

15. System is ready for remote control (computer control) 

16. Document History 

Versio

n 

Version 

Date Author Page Total

Revision

 Date 

Revision

Date 

Revision 

 Date 

Revision

Date 

1.0 26-Jun-06 C. Gibson 2 

 

 

 

 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR11 1.0 26-Jun-06 C. Gibson 1 of 2 IRR-CP-IRR11 Reset Linear 

Encoder v1.doc 
F69 

Irradiance Calibration Procedure 

IRR-CP-IRR11-Reset Linear Encoder

Figure IRR11.1 Front panel of HEIDENHAIN Linear Encoder Display Unit 

Figure IRR11.2 Front panel of UNIDEX 511 Motion Controller 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR11 1.0 26-Jun-06 C. Gibson 2 of 2 IRR-CP-IRR11 Reset Linear 

Encoder v1.doc 
F70 

Irradiance Calibration Procedure 

IRR-CP-IRR12-Goniometric Scan

Goniometric scan

LASER 

COLLISION 

1. The quartz halogen lamp (QHL) is spatially mapped by rotating the about the vertical and 

horizontal axes. This method approximates the irradiance in a plane 50 cm in front of the 

lamp. The center of rotation of the NIST-designed gonio stage is determined and then the 

QHL lamp is placed at the center of rotation of the stage. The QHL is placed at the center of 

rotation to measure irradiance differences attributed to the QHL uniformity. If the lamp is 

not located at the center of rotation of the stage then the lamp will translate along the vertical 

and horizontal axes resulting in measurements of different portions of the lamp. 

2. Align the QHL alignment jig at 50 cm in test position #4 

3. Leave the spectroradiometer laser on 

4. Place the pointer in the lamp socket 

5. Set the pointer height to the center of the laser using the translation stage above the gonio 

stage 

6. Install the scope in test position #1 

7. Align the scope normal to the optical axis 

8. Align the scope target on the pointer tip 

9. Center the pointer about the vertical axis 

9.1. Place a card in front of pointer to view the pointer shadow formed by the laser beam 

9.2. Center the pointer on the laser beam 

9.2.1. If the pointer is not centered on the laser beam then re-center the pointer by 

adjusting half the distance using the translation stage above the gonio stage and the 

other half using translation stage below the gonio stage 

9.3. Rotate the mount +90° about the vertical axis 

9.4. Repeat steps until pointer is centered as it rotates about the vertical axis 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR12 1.0 30-Jun-06 C. Gibson 1 of 5 IRR-CP-IRR12 Goniometric 

Scan v1.doc 
F71 

Irradiance Calibration Procedure 

IRR-CP-IRR12-Goniometric Scan

10. Center the pointer about the horizontal axis 

10.1. Rotate the pointer +7°about the horizontal axis 

10.2. Look through the scope 

10.3. Rotate back to the center 

10.4. If the center of rotation is below the optical axis then raise the translation stage above 

the gonio stage and lower the translation stage below the gonio stage 

10.5. If the center of rotation is above the optical axis then lower the translation stage above 

the gonio stage and lower the translation stage raise the gonio stage 

10.6. Rotate the pointer -7°about the horizontal axis 

10.7. Look through the scope 

10.8. Rotate back to the center 

10.9. If the center of rotation is below the optical axis then raise the translation stage above 

the gonio stage and lower the translation stage below the gonio stage 

10.10.If the center of rotation is above the optical axis then lower the translation stage above 

the gonio stage and lower the translation stage raise the gonio stage 

10.11.Repeat steps until pointer tip is centered as it rotates about the horizontal axis 

11. Align the alignment jig on the optical axis 

11.1. Align the scope target on the pointer tip 

11.2. Tape down the translation stage handles for the stage below the gonio stage (No 

further adjustments are made to this stage) 

11.3. Remove the rotation stage handle 

11.4. Attach the DC motor to the rotation stage 

11.5. Install the alignment jig and align 

11.6. Set distance using position indicated by scope 

11.7. Use translation stage below the gonio stage to translate along the optical axis 

11.8. Re-tape the translation stage handle for the stage below the gonio stage 

11.9. For other adjustments, use the translation stage above the gonio stage or the gonio 

stage to align the jig on the optical axis 

11.10. Reset the scope to center on the alignment jig 

11.11. Set the rotation stage dial to zero 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR12 1.0 30-Jun-06 C. Gibson 2 of 5 IRR-CP-IRR12 Goniometric 

Scan v1.doc 
F72 

Irradiance Calibration Procedure 

IRR-CP-IRR12-Goniometric Scan

11.12. Mark the starting position of the gonio stage horizontal dial with a piece of masking 

tape 

11.13. Connect motor cables 

11.14. Turn on Aerotech controller if necessary 

12. Remove alignment jig 

13. Install lamp in lamp socket 

14. Turn on lamp 

15. Run goniometric scan program 

15.1. From Hardware.frm, click Tests then Spatial Scan in the program menu 

15.2. Enter the Filename

15.3. Select the Increment size [deg]

15.4. Enter the Number of reading per Trigger

15.5. Enter Degrees of rotation about the vertical axis (<Y) 

15.6. Enter Degrees of pitch about the horizontal axis (<X) 

15.7. Select axis to measure 

15.7.1. The program by default select the following when the program is run 

15.7.2. <X - Rotation about the horizontal axis 

15.7.3. <Y - Rotation about the vertical axis

15.8. Select scan type 

15.8.1. Select Goniometric scan

15.9. Click Start Scan to run program 

15.10. Click Test Motor to text motor selected in select axis to measure 

15.11. Click Initialize AERO3 to initialize stepper motor controller 

15.11.1. Program initializes this controller when Start Scan is clicked 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR12 1.0 30-Jun-06 C. Gibson 3 of 5 IRR-CP-IRR12 Goniometric 

Scan v1.doc 
F73 

Irradiance Calibration Procedure 

IRR-CP-IRR12-Goniometric Scan

16. Document History 

Version Version 

Date Author Page 

Total 

Revision 

 Date 

Revision 

Date 

Revision 

 Date 

Revision 

Date 

1.0 30-Jun-06 C. Gibson 5 

 

 

 

 

Figure IRR12.1. Front panel of Spatial.frm

Procedure Version Date Author Pages Filename 

IRR-CP-IRR12 1.0 30-Jun-06 C. Gibson 4 of 5 IRR-CP-IRR12 Goniometric 

Scan v1.doc 
F74 

Irradiance Calibration Procedure 

IRR-CP-IRR12-Goniometric Scan

Figure IRR12.2. Sample goniometric scan data 

Procedure Version Date Author Pages Filename 

IRR-CP-IRR12 1.0 30-Jun-06 C. Gibson 5 of 5 IRR-CP-IRR12 Goniometric 

Scan v1.doc 
G1

Appendix G. Radiation constants

c = speed of light in vacuum

c1L = first radiation constant for spectral radiance = 2 h c2

c2 = second radiation constant = h c k-1

h = Planck constant = 6.626 069 57 (29) × 10-34 J s = 6.626 069 57 × 10-34 W s2

k =Boltzmann constant = 1.380 6488 (13) × 10-23 J K-1= 1.380 6488 × 10-23 W s K-1

n = refractive index of air at 655 nm at 15 °C and 101325 Pa = 1.00028

c1L c2 c

Area in m2, wavelength in m 1.191 042 869 (53) 10-16 W m2

sr-11.438 7770 (13) 10-2 m K 2.997 924 58 108 m s-1

Area in m2, wavelength in cm 1.191 042 869 10-8 W m2

sr

-1

1.438 7770 cm K 2.997 924 58 1010

cm s

-1

Area in m2, wavelength in m 1.191 042 869 108 W m2sr

-1

1.438 7770 104 m K 2.997 924 58 1014m s

-1

Area in m2, wavelength in nm 1.191 042 869 1020 W m2

sr-11.438 7770 107nm K 2.997 924 58 1017 nm s-1

Area in cm2, wavelength in cm 1.191 042 869 10-12 W cm2

sr-1

1.438 7770 cm K 2.997 924 58 1010 cm s-1

Area in cm2, wavelength in m 1.191 042 869 104 W cm2sr-11.438 7770 104 m K 2.997 924 58 1014m s-1

Area in cm2, wavelength in nm 1.191 042 869 1016 W cm2

sr

-1

1.438 7770 107nm K 2.997 924 58 1017nm s

-1

Area in m

2

, wavelength in m 1.191 042 869 10-4 W m

2

sr

-1

1.438 7770 104 m K 2.997 924 58 1014m s

-1

Area in nm2, wavelength in nm 1.191 042 869 102 W nm2

sr-11.438 7770 107nm K 2.997 924 58 1017 nm s-1

Source of the CODATA internationally recommended values

The values of the constants provided at this table are recommended for international use by CODATA and are the latest available. 

Termed the "2010 CODATA recommended values," they are generally recognized worldwide for use in all fields of science and 

technology. The values became available on 2 June 2011 and replaced the 2006 CODATA set. They are based on all of the data 

available through 31 December 2010. The 2010 adjustment was carried out under the auspices of the CODATA Task Group on 

Fundamental Constants.
H1

Appendix H. Conversion factors

Spectral radiance Spectral irradiance

To convert

from cm-2cm-1

multiply by

Area in m2, wavelength in m W m-2m

-1

sr-1 W m-2m

-1

106

Area in m2, wavelength in cm W m-2cm

-1

sr

-1 W m-2

cm

-1

104

Area in m2, wavelength in m W m-2m

-1

sr

-1 W m-2

m

-1

1

Area in m2, wavelength in nm W m-2nm

-1

sr

-1 W m-2

nm

-1

10-3

Area in cm2, wavelength in cm W cm-2cm-1sr-1 W cm-2cm-11

Area in cm2, wavelength in m W cm-2m

-1

sr

-1 W cm-2

m

-1

10-4

Area in cm2, wavelength in m mW cm-2 m

-1

sr-1 mW cm-2 m

-1

10-1

Area in cm2, wavelength in nm W cm-2nm-1sr-1 W cm-2nm-110-7

Area in cm2, wavelength in nm mW cm-2nm-1sr-1 mW cm-2nm-110-4

Area in cm2, wavelength in nm W cm-2

nm-1sr-1 W cm-2nm-1

10-1
I1

Appendix I. Alignment jig

Figure I1. Dimensional drawing of alignment jig

1.9

Front view Side view

9.5

4.8

2.25 0.64

1.9

2.05

2.22

8.41

All dimensions in cm

Flat glass 

plate parallel 

to plane of 

both rods

Epoxy 

encapsulating 

compound
J1

Appendix J. Kinematic lamp socket
K1

Appendix K. Calibration data points

Spectral irradiance is measured at the following wavelengths

Wavelength [nm] Wavelength [nm]

250 555

260 600

270 654.6

280 700

290 800

300 900

310 1050

320 1150

330 1200

340 1300

350 1540

360 1600

370 1700

380 2000

390 2100

400 2300

450 2400

500
L1

Appendix L. Calibration services

The Spectroradiometric Sources Calibration services include the following.

Service 

ID

Number Description of Services

NIST calibrates and issues a 1000 W, tungsten quartz-halogen lamp 

mounted in a medium bi-post base. The calibrations are performed at 

50 cm.

39030C Spectral Irradiance Standard, 1000 W Tungsten Quartz–

Halogen Lamp (250 nm to 450 nm)

39031C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(250 nm to 450 nm)

39032C Spectral Irradiance Standard, 1000 W Tungsten Quartz–

Halogen Lamp (350 nm to 800 nm)

39033C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(350 nm to 800 nm)

39040C Spectral Irradiance Standard, 1000 W Tungsten Quartz–

Halogen Lamp (250 nm to 1600 nm)

39041C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(250 nm to 1600 nm)

39045C Spectral Irradiance Standard, 1000 W Tungsten Quartz–

Halogen Lamp (250 nm to 2400 nm)

39046C Recalibration of 1000 W Tungsten Quartz–Halogen Lamp 

(250 nm to 2400 nm)

39060S Special Tests of Radiometric Sources

Descriptions of these services can be found on the NIST Calibrations webpage.

Spectroradiometric Calibration Services

(http://www.nist.gov/calibrations/spectroradiometric.cfm)