NATIONAL BUREAU OF STANDARDS REPORT

10 005

LAMPS FOR INTERNATIONAL INTERCOMPARISONS

TO BE CARRIED OUT AT

BUREAU INTERNATIONAL DES POIDS ET MESURES

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3, 1901. Today, in addition to serving as the Nation’s central measurement laboratory,

the Bureau is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To this end the Bureau conducts research and

provides central national services in three broad program areas and provides central national services in a fourth. These are: (1) basic measurements and standards,

(2) materials measurements and standards, (3) technological measurements and

standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, and the Center for Radiation Research.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the

United States of a complete and consistent system of physical measurement, coor- dinates that system with the measurement systems of other nations, and furnishes

essential services leading to accurate and uniform physical measurements throughout

the Nation’s scientific community, industry, and commerce. The Institute consists

of an Office of Standard Reference Data and a group of divisions organized by the

following areas of science and engineering

:

Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic Physics—Cryogenics2 —Radio Physics2—Radio Engineering2—Astrophysics2—Time

and Frequency.2 THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to methods, standards of measurement, and data needed by industry, commerce,

educational institutions, and government. The Institute also provides advisory and

research services to other government agencies. The Institute consists of an Office of

Standard Reference Materials and a group of divisions organized by the following areas of materials research:

Analytical Chemistry—Polymers—Metallurgy — Inorganic Materials — Physical

Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides for the creation of appropriate opportunities for the use and application of technology within the Federal Government and within the civilian sector of American industry. The primary functions

of the Institute may be broadly classified as programs relating to technological meas- urements and standards and techniques for the transfer of technology. The Institute

consists of a Clearinghouse for Scientific and Technical Information,3 a Center for

Computer Sciences and Technology, and a group of technical divisions and offices organized by the following fields of technology:

Building Research—Electronic Instrumentation — Technical Analysis — Product

Evaluation—Invention and Innovation— Weights and Measures — Engineering

Standards—Vehicle Systems Research.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement,

and application of radiation to the solution of Bureau mission problems and the

problems of other agencies and institutions. The Center for Radiation Research consists of the following divisions:

Reactor Radiation—Linac Radiation—Applied Radiation—Nuclear Radiation.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D. C. 20234.

2 Located at Boulder, Colorado 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia 22151.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

2120113 March 5, 19.69, NBS REPORT

10 005

LAMPS FOR INTERNATIONAL INTERCOMPARISONS

TO BE CARRIED OUT AT

BUREAU INTERNATIONAL DES POIDS ET MESURES

by

Donald A. McSparron

Photometry Section

Metrology Division

Institute for Basic Standards

IMPORTANT NOTICE NATIONAL BUREAU OF S

for use within the Government, and review. For this reason, tl whole or in part, is not authi Bureau of Standards, Washing

the Report has been speciticall

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

ess accounting documents intended

s subjected to additional evaluation

e listing of this Report, either in he Office of the Director, National by the Government agency for which

copies for its own use. <^BS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
>•
THE LUMINOUS INTENSITY OF 16 LAMPS

AND

THE LUMINOUS FLUX OF 8 LAMPS

FOR

INTERCOMPARISONS TO BE CARRIED OUT

AT

BUREAU INTERNATIONAL DES POIDS ET MESURES

by

Donald A. McSparron

I. PURPOSE AND SCOPE

Since 1948 the National Bureau of Standards has participated in

the First!/, Second!/, Third!', and Fourth!' Comparisons of National

Photometric Standards of Intensity and Flux. The present report covers

the preparation of standards of luminous intensity at 2042 K and 2854 K

and standards of luminous flux at 2788 K for the Fifth Comparison of

National Photometric Standards. A description of the present reference

standards maintained at NBS and the recent program to recheck their values

will also be given.

II. INTRODUCTION

As part of the national measurement system the National Bureau of

Standards maintains reference groups of lamp standards of luminous intensity

at 2042 K, 2360 K and 2854 K and also reference groups of lamp standards of

luminous flux at 2360 K and 2788 K. Periodically these derived groups of

reference standards are referred to a blackbody at the freezing point of

platinum. The last time such a comparison was made was in 1958. In order

to firmly establish a unified photometric system and also to prepare for NBS

participation in the Fifth Comparison of National Photometric Standards, a program was begun two years ago to rederive the NBS units of luminous intensity

at 2360 K and 2854 K, and also the NBS unit of luminous flux at 2788 K. Since

this work will be reported in detail elsewhere, only a summary will be presented here. Since the NBS international standard of luminous intensity, a blackbody at the freezing point of platinum, was not operative at the time

this work was begun, the NBS reference lamp groups (BS 2395 and NBS 839) at

2042 K, which had been calibrated in terms of the international standard in

1937 and 1958 respectively, were assumed to accurately embody the defined

unit of luminous intensity. Direct comparison showed these two groups to

be in disagreement by 0.27 °h. Accordingly the grand mean of the 16 lamps in

these two groups was held constant and the mean values of each group adjusted

by 0.135 %. Hence it is considered that no change has been made in the NBS

candela at 2042 K.

- 2 -

The reference lamp standards of luminous intensity at 2360 K and 2854 K were derived from the 2042 K reference groups by means of: 1) a blue filter

,

2) a yellow filter, 3) a physical photometer 5/ and 4) a spectroradiometer

.

The results obtained by these various methods initially showed systematic

disagreements. The major cause of these observed disagreements was the

filter transmittances, which had been determined by means of a spectrophotometer. The particular blue and yellow filters used were several millimeters thick, and it is believed that the optical differences between the

spectrophotometric and photometric procedures invalidate the transmittances

so determined. Hence, these transmittances were not used. Instead, the

filter transmittances were determined on the physical photometer. Then the

observed range of data for the four methods used was 0.7 % for the 2042 K-2360

K transfer and also for the 2360 K-2854 K transfer. The results of this work

indicate a decrease of 0.4 % in the size of the NBS unit of luminous intensity

at 2360 K and no change in the size of the unit at 2854 K.

The NBS reference standards of luminous flux at 2788 K are based on a group of 300-watt opal-bulb transfer standards (NBS 526) . Extensive distribution photometry had been performed on these lamps in 1938 and again in

1958. The results of these two extensive sets of measurements were in

agreement, and so no further distribution work was done at this time. The

luminous intensity in a specified direction was redetermined for this group

of opal -bulb lamps. From these values of luminous intensity and the previous

distribution work, values of total luminous flux were computed for this

group of lamps. The results indicate a decrease of 0.25 °L in the size of

the unit of luminous flux at 2788 K, from the values reported in the Fourth

Comparison of National Photometric Standards of Intensity and Flux.

In the report covering the work done at NBS for the Fourth Comparison

of National Photometric Standards of Intensity and Flux (NBS Report #6979),

NBS announced the intention to adjust the size of the United States unit

of luminous flux at 2788 K to bring it into accord with the units as realized

in other national standardizing laboratories. Implementation of this decision

was delayed pending the completion of the recheck work described above. Now

the intention is to adjust, on the basis of this recheck work, the United

States photometric units at the close of the present international intercomparison.

In all cases, both for values of luminous intensity and for values of

luminous flux, lamp values given in this report incorporate the results of

the most recent recheck work.

Ill . MATERIAL

In preparation for the Fifth Comparison of National Photometric

Standards of Intensity and Flux, the Consultative Committee on Photometry

decided that the Bureau International des Poids et Mesures should make

arrangements for the manufacture, selection, seasoning, and procurement of

lamps to be used in the intercompar ison^./ . After such arrangements had been

made, each national laboratory participating in the intercomparison procured

the required number of lamps directly from the selected lamp companies. In

-3-

addition to the lamps, each lamp manufacturer supplied the electrical

operating characteristics and alignment procedures to be used in assigning

the lamps. Accordingly NBS purchased ten each of the following types of

lamps

:

1. 10-volt, 5.5-ampere, 15-candela lamps manufactured by the Tokyo

Shibaura Electric Company, Ltd., of Tokyo, Japan, to be calibrated for

luminous intensity at 2042 K.

2. 30-volt, 6-ampere, lamps, type Wi 41/G manufactured by the Osram

Lamp Company, of Berlin, Germany, to be calibrated for luminous intensity at

2 854 K.

3. 100-volt, 200-watt flux standards manufactured by Osram, GEC, Ltd.

of Wembley, Middlesex, England, to be calibrated for total luminous flux at

2788 K.

After calibration, eight lamps from each of these three groups were sent

to the Bureau International des Poids et Mesures; the remaining two lamps of

each group were retained at NBS.

IV . STANDARDS

Each group of lamps was calibrated in terms of the NBS group of

reference standards for the respective photometric unit. These groups of

reference standards are as follows:

1. Candela at 2042 K. This group consists of lamps NBS 839, NBS 840,

NBS 841, NBS 842, NBS 843, NBS 844, NBS 845 and NBS 846. These lamps were calibrated in 1958 against a blackbody radiator at the freezing point of

platinum. The group relative values were adjusted in 1968 as explained in

section II. The mean intensity of the eight lamps of the NBS 839 group is

15. 79^ candelas.

2. Candela at 2854 K. This group consists of lamps NBS 5612, NBS 5613,

NBS 5614, NBS 5615, NBS 5616, NBS 5617, NBS 5618, NBS 5619, NBS 5620 and

NBS 5621. These lamps were calibrated in 1968 by the methods discussed in

section II of this report. The mean intensity of the ten lamps is 633.5

candelas

.

3.

Lumen at 2788 K. Two groups of standards were used for this comparison. One group of lamps, the opal-bulb lamps, consists of lamps NBS 526,

NBS 527, NBS 528, NBS 529, NBS 530 and NBS 531. The mean luminous flux of

these six lamps was found to be 2760. g lumens in 1968 by the methods described

above. The second group consists of lamps NBS 6807, NBS 6808, NBS 6810, NBS

6812, NBS 6814 and NBS 6815. The mean luminous flux of these lamps was determined

in 1968 in terms of the NBS 526 group and is 3242.5 lumens. Values determined

with these two groups differed by C . 12 % on the average. Since the NBS 6807

group is assigned in terms of the NBS 526 group, data taken with the NBS 6807

group was given a weight of 1/2 (a statistically valid number which takes into

account the length of the unit chain) in assigning values to the lamps submitted

to the Bureau International des Poids et Mesures.

-4-

V. EQUIPMENT AND PROCEDURES

To provide an index of the reproducibility and stability of the

results, the test lamps and the reference standards were compared at least

five times in a series of measurements extending over a period of at least

two months.

All measurements were made photoelectrically by using barrier-layer

photocells equipped with filters to correct the spectral response to approximate that of the CIE photopic spectral luminous efficiency function. Measurements of luminous intensity at 2042 K and 2854 K were made with a "balance"

circuit photometer in which the currents of two photocells, one illuminated

by the test lamp and one by a comparison lamp, are balanced by adjusting the

distance between the comparison lamp and photocell; the relative lamp

intensities were computed from the squares of the distances. Measurements

of luminous flux were made with a zero-resistance photometer .]_/

All measurements of luminous intensity were made by a substitution

method on a horizontal bar photometer with all lamps operating vertically in

a base -down position. The measurements of luminous flux were made by a substitution method in an 80-inch integrating sphere. The lamps were operated

in a base-up position. The sphere was coated with Burch sphere paint and a blue glass filter was used to compensate for the effect of spectral selectivity

of the sphere coating.

1. Luminous Intensity at 2042 K. The clear, spherical-bulb test lamps were received from the manufacturer with markings on the base to indicate the

polarity of the applied potential and also arrows which were to face the

receiver. The lamps were scribed on the metal base with the numbers listed

in Table 1. In addition a circle was scribed on the base on the side opposite

the arrow. In operation the circle was away from the receiver, and hence the arrow was toward the receiver as specified by the manufacturer. These lamps were oriented by projecting the shadow of the filament by means of an auxiliary projector so that the plane of the filament was perpendicular to

and centered on the photometer axis. The voltage applied to the terminals

of the lamps was fixed at the values listed in Table 1. and readings were

taken of the current and luminous intensity of the lamps. The polarity was

fixed in the manner specified by the manufacturer. The photometric distance

was 1.50 meters.

2. Luminous Intensity at 2854 K. The conical-bulb test lamps have one half their surface blackened, except for a small clear window to permit

viewing of the filament. The numbers listed in Table 2 were etched on the

necks of the bulbs. The lamps were oriented with the blackened half of the

bulb and window toward the receiver. The lamps were aligned by projecting

the shadow of the filament by means of an auxiliary projector so that the

plane of the filament was perpendicular to and centered on the photometer

axis. The voltage applied to the base of the lamps was set at the values

listed in Table 2 and readings taken of the current and luminous intensity.

The photometric distance was 1.50 meters. Note is made of the fact that

these lamps should have been set by current rather than by voltage. It is
'
-5-

understood that they will be set at: the values of current listed in

Table 2 when they are measured at BIPM and they will also be so set when

they are returned for measurement at NBS.

3. Luminous Flux at 2788 K. All of the clear spherical-bulb test

lamps were operated in a base-up position. The numbers listed in Table 3 were etched on the necks of the bulbs. The voltage applied to the base of

the lamps was set at the values listed in Table 3 and readings taken of the

current and luminous flux of the lamps. An unlighted standard was in place

in the sphere when readings were made on the test lamps to compensate for

the effects of self absorption of the lamps. Similarly an unlighted test

lamp was in place in the sphere when readings of the standards were taken.

VI. RESULTS

The results are given in Tables 1, 2 and 3. In Tables 1 and 2 the

values reported for current and luminous intensity are the averages of five

measurements taken over a period of two months. The values of luminous

flux reported in Table 3 are the weighted average of six measurements taken

over a period of three months.

VII. UNCERTAINTY

Indices of the precision of the values reported in the above tables were computed on the basis of pooling the data on the individual lamps in

each group (including the lamps retained at NBS)

.

1. Luminous Intensity at 2042 K. A pooled estimate of the standard

deviation of a single measurement was computed on the basis of 40 degrees

of freedom to be 0.42 %. Accordingly a 3-sigma limit for the mean intensity

of the eight lamps submitted to the Bureau International des Poids et Mesures

is 0.21 % (or 0.033 candela) based on five measurements on each of the eight

lamps submitted.

2. Luminous Intensity at 2854 K. A pooled estimate of the standard

deviation of a single measurement was computed on the basis of 40 degrees of

freedom to be 0.50 7c. Accordingly a 3-sigma limit for the mean intensity of

the eight lamps submitted to the Bureau International des Poids et Mesures

is 0.24 7c (or 0.63 candela) based on 5 measurements of each of the eight

lamps submitted.

3. Luminous Flux at 2788 K. Pooled estimates of the standard deviation

of a single measurement were computed on the basis of 18 degrees of freedom

each for the measurements against the NBS 526 group and for the measurements

against the NBS 6807 group. These were 0.21 7c and 0.30 % respectively.

Applying the factors appropriate to the weighting described above, a 3-sigma

limit for the mean flux of the eight lamps submitted to the Bureau International des Poids et Mesures is 0.11 7c (or 2.7 lumens).

- 6 -

In all cases these values of the uncertainties apply only to the

precision of the transfer of the NBS unit to the various lamps submitted

to the Bureau International des Poids et Mesures. No allowance has been

made for possible systematic errors in the NBS standards.

Table 1

Luminous Intensity at 2042 K; measurements taken after 15

minutes warm-up time

Lamp

Number

Potential

(Volts)

(Set)

Current

(Amperes)

Luminous Intensity

(Candelas)

NBS 8460 10.375 5.357 15.13

NBS 8461 10.385 5.353 15.14

NBS 8462 10.380 5.371 14.98

NBS 8463 10.425 5.345 15.18

NBS 8464 10.460 5.383 15.16

NBS 8465 10.385 5.344 15.07

NBS 8466 10.385 5.376 15.17

NBS 8467 10.430 5.358 14.95

15.098

Table 2

Luminous Intensity at 2854 K; measurements taken

after 10 iminutes warm-up time

Lamp Potential Current Luminous Intens

Number (Volts)

(Set)

(Amperes) (Candelas)

NBS 8358 31.65 5.8870 260.1

NBS 8360 31.97 5.8570 270.7

NBS 8361 31.86 5.8720 267.2

NBS 8362 32.14 5.9140 262.8

NBS 8363 31.79 5.8570 264.0

NBS 8364 31.52 5.9970 264.2

NBS 8365 31.23 5.8780 256.6

NBS 8366 31.65 5.7960 258.6

262.46

Table 3

Luminous Flux at 2788 K; measurements taken

after 10 minutes warm-up time

Lamp

Number

Potential

(Volts)

(Set)

Current

(Amperes)

Luminous Flux

(Lumens)

NBS 8380 95.70 2.050 2538

NBS 8381 95.30 2.034 2505

NBS 8382 96.40 2.054 2627

NBS 8383 96.90 2.036 2621

NBS 8384 97.80 2.025 2600

NBS 8385 96.00 2.037 2538

NBS 8386 97.80 2.069 2671

NBS 8387 94.90 2.042 2506

2575.8

REFERENCES

1. Comite Consultatif de Photometrie, Session de 1952, Proces-Verbaux

des Seances, Annexe P3, 46-75

2. Same Annexe P4, 76-100

3. Comite Consultatif de Photometrie, 4 Session (1957), ProcesrVerbaux

des Seances, Annexe P8, 74-103

4. Comite Consultatif de Photometrie, 5

e Session (1962) Annexe 9, 63-87

5. R. P. Teele, A Physical Photometer, J. Op. Soc. Am., Vol. 31, 696-704

November, 1941

6. Recommendation P4, Consultative Committee on Photometry, 6th Session

7. L. E. Barbrow, A Photometric Procedure Using Barrier-Layer Photocells

NBS J. Research 25, 703 (December, 1940) RP1348

)I
1I