O-1 New Standards for Reflected Color

Color standards is the area that elicited the most response in the optical properties of materials
category. This interest is being driven by the increased attention to color quality in consumer
products, to color discrimination in various tests, including for the presence of chemical and
biological agents, and to color reproduction on computer screens and printers for electronic
commerce. To meet the needs in these areas as well as others, the CORM 7° Report
recommends the following:

« Improve the referee capability to measure spectrally using total hemispherical and bi-
directitional (45/0 or 0/45) reflectance factor measurements in order to correspond to
the instruments in common industrial use. Industry is currently in need of reflectance
uncertainties on the order of +/- 0.0003; a full order of magnitude better than what is
currently available from NIST.

© Plan and initiate a measurement assurance program suitable for verification of the
measurement capabilities of calibration and testing laboratories.

e Provide, singly and in cooperation with CIE, CORM and other organizations,
educational programs to industrial users emphasizing the SRMs, measurements
available at NIST and the uncertainties involved in the measurement process.

¢ Facilitates measurements at multiple angle combinations for gonioapparent materials,
with uncertainties of less than 0.5 CIELAB color difference unit.

In response to needs articulated by members of CORM, the Inter-Society Color Council (ISCC),
the ASTM International Committee E-12 on Color and Appearance, and other industry groups,
NIST has developed a new reference instrument for measuring reflectance color [5,6], as
pictured in Figure 9. The NIST Reference Reflectance Colorimeter presently has capabilities for
determining the bidirectional reflectance factor in the standard 0°/45° or 45°/0° geometry.
Efforts are presently underway to develop capabilities for measuring the reflectance factor for
the total hemispherical geometry and for arbitrary input and output angles.

The 0°/45° or 45°/0° measurements are available to NIST customers through the NIST
Calibration Services under Special Tests of Spectral Reflectance and Surface Color, number
38060S. The typical submitted test item is a set of twelve to fourteen standard 10 cm square
BCRA glossy color tiles. Measurements of the reflectance factor are performed from 380 nm to
780 nm in 5 nm steps for both parallel and perpendicular polarizations of the incident radiation.
The results for the two polarizations are averaged. The reflectance factors are referenced to the
reflectance of a Spectralon’ polytetrafluoroethylene standard as determined using the NIST
Spectral Tri-function Automated Reference Reflectometer or STARR. Although the
measurement uncertainty on the reflectance factor varies with wavelength and color of the tile,
typical values are less than 0.0003 (k = 2), the stated requirement in the CORM 7" Report.


e NIST continues to support and expand its ongoing contacts with critically impacted
industries through participation in industry conferences, standards group participation,
and technical briefs directed to identifiable segments of the NIST constituency.

e NIST promotes the proper use of the recently improved uncertainty of its irradiance
scale among its known constituents.

e NIST continues to support its aggressive program of development of multiple
approaches for realization and maintenance of the spectral irradiance scale. This is a
strength that NIST is fully capitalizing on and is the basis of the improved spectral
irradiance scale. It is important to continue to support the multiplex approach. This
includes continued development of an overall laboratory design and systems
automation that facilitate the interaction of complementary methods such as SURF,
SIRCUS, LBIR, etc.

NIST continues to work with industry in the development and dissemination of spectral
irradiance measurements and standards. These activities include collaborating with the
American Water Works Association Research Foundation (AwwaRF) in developing ultraviolet
irradiance calibration standards for water treatment; with heat flux sensor manufacturers and
users within the aerospace and fire testing community in improving radiative heat flux (i.e., total
irradiance) measurements (see Figure 5); with the U.S. solar U.V. monitoring community to
ensure the accuracy of their spectral irradiance standards; with remote sensing researchers to
validate spectral radiance scales obtained from NIST spectral irradiance lamp standards; and
with the DoD to improve the dissemination of spectral irradiance standards throughout the
defense community.

To assist industry and government in improving their use of spectral irradiance measurements
and standards, NIST developed a new short course on Spectroradiometry in 2002, modeled after
the successful Photometry and Radiance Temperature Short Courses. The Spectroradiometry

Water-cooled end caps Cavity
radiometer

Extension Heat flux
(uncooled) Sensor

Graphite tube cavity,

heated section

Partition Aperture

‘Aperture diameter: 25mm
Purge gas: Argon
Temperature (maximum): 2973 K
Heat flux at sensor: 50 KWinf

Computer Power supply

Figure 5. Schematic diagram of the Radiative Heat Flux Calibration Fa:

ty [15].


0-5 Measurement and Standards for Retroreflection

The old NIST retroreflectance facility became dysfunctional over 15 years ago and could not be
used for the measurement assurance program or for calibrations. CORM and others have
requested for many years that NIST reestablish this capability to support the highway marking
industry and others that use retroreflective materials. The U. S. Department of Transportation
has identified correct characterization of highway marking materials to be a critical element of
highway safety and is working with the various states to develop appropriate measurement
assurance programs. The CORM 7 report recommends that NIST;

© Reestablish state of the art, retroreflectance measurement instrumentation for the
calibration of transfer materials and to conduct measurements. This should emphasize
testing of retroreflective road marking materials as well as the geometric aspects of
newer microprismatic signing materials. Measurements of pavement markings at 1.05
degrees observation angle and 88.76 degrees entrance angle is needed. Measurement
of sign sheeting at a variety angles, including 0.2 degrees observation and —4 degrees

entrance angle, is needed.

« Provide a spectral retroreflectance measurement service. This includes the capability to
measure spectral retroreflectance of all types of retroreflective materials and devices.
Spectral measurements form the basis for color control and classification.

¢ Re-establish the NIST
retroreflectance Measurement
Assurance Program and _ the
associated SRM’s necessary to
allow secondary laboratories and
testing laboratories to confirm the
accuracy of their retroreflectance
measurements.

NIST has recently completed a state-of-the-
art facility for retroreflectance
measurement with funding from the
National Cooperative Highway Research
Program (NCHRP) through project 05-16,
National Calibration Facili for
Retroreflective Traffic Control Materials.
NIST completed this project and the
development of the facility in 2004; an
official calibration service for
retroreflective materials will be launched in

Figure 11. A STOP sign be mounted in the new NIST
retroreflectance measurement facility.

22


Preface

The Council for Optical Radiation Measurement or CORM began as a non-profit organization in
1972. CORM serves the interests of professionals and institutions engaged in optical radiation
measurements, with representatives from a wide range of industrial sectors. CORM’s purpose as
stated on their website, www.corm.org, is

e To establish (and publish) consensus among interested parties on national, industrial and
academic requirements for physical standards, calibration services, and inter-laboratory
collaboration programs in the fields of optical radiation measurement, including
measurement of the transmittance and reflectance properties of materials, measurement
of radiant sources, and characterization of optical detectors used for the measurement of
these properties.

¢ To establish national consensus on the priorities for these requirements.

e To maintain liaison with the National Institute of Standards and Technology (NIST) and
to advise the Institute of requirements and priorities.

¢ To cooperate with other organizations, both public and private, to accomplish these
objectives for the direct and indirect benefit of the public at large.

e¢ To assure that information on existing or proposed standards, calibration services,
collaboration programs, and its own activities is widely disseminated to interested parties.

¢ To answer inquiries about such standards activities or to forward such inquiries to the
appropriate agencies.

To establish a consensus on issues in the optical radiation measurement community, CORM
periodically surveys its members and other interested parties on needs in optical radiation
measurements. This community encompasses diverse interests from the university or
government scientist using remote sensing satellites to study the earth to industrial scientists and
engineers using optical measurement to assess the performance and quality of products after
manufacture. The survey results are analyzed and recommendations for action are issued in a
special CORM report. The most recent CORM report, the 7 prepared by the CORM 7 Report
committee in partnership with the CORM Board of Directors and Officers, was released in 2001
[1]. The needs identified from the survey were separated into three broad categories: radiometry,
optical properties of materials, and measurement uncertainty.

Many of the needs fall within the purview of NIST’s mission as the Nation’s primary
measurement and standards laboratory, while other needs are better addressed by industrial or
academic laboratories. The present report presents NIST’s response to the needs identified by
CORM. NIST’s ability to respond to these needs is, of course, dependent on the available
resources and synergy with the laboratory mission.

For the purposes of this response, quotes from the CORM 7" Report are given in bold italics.


Figure 9. Picture of the new NIST Reference Colorimeter with sample wheel for 0/45
measurements of reflected color.

NIST is working to ensure the quality of color measurements by calibration and testing
laboratories and instrument manufacturers by participating in proficiency testing programs
offered by independent testing services. This approach allows NIST to leverage the extensive
measurement comparison infrastructure developed by independent testing services to effectively
assess the performance of industry laboratories in making measurements comparable nationally
and internationally against national and international standards. Measurement comparisons with
other National Metrology Institutes (NMIs) have also been undertaken to aid calibration and
testing laboratories and instrument manufacturers in ensuring that their measurements are
comparable internationally.

As part of its development of measurements methods and standards for reflected color, NIST has
undertaken an analysis of uncertainties in the measurement of 0/45 reflected color. In an effort
to communicate this work to color measurement practitioners, NIST staff members have
presented the results at meetings of CORM, ISCC, and ASTM and have published a paper on the
subject [20].

Finally, as part of its color measurement research, NIST is developing the capability for full
goniometric measurements of reflected color at arbitrary input and output angles. This capability
is expected to be fully implemented in the near future and will allow full characterization of
gonioapparent materials.

0-2 New Standards for BRDF/BTDF
Standards for BRDF/BTDF (bidirectional reflectance/transmittance distribution function)

measurements were requested in the CORM 6" Report and have been of interest to NIST’s
customers for many years, While NIST has measurement programs and calibration services in


A significant number of CORM Seventh Report
surveys (72%) noted that a need exists to
“reduce the measurement uncertainty” of
optical radiation measurement parameters and
a “better understanding of the concept of
measurement uncertainty” is needed.

The report recommends that NIST strive to lower
the uncertainties of the calibration artifacts used
for disseminating spectral irradiance, spectral
radiance, and other radiometric and photometric
scales. In response, NIST is working to reduce
the uncertainties of the fundamental photometric
and radiometric scales disseminated to U.S.
industry and government by leveraging recent
advances in laser technology, cryogenic
radiometry, and detector-based radiometry, as
illustrated by HACR II (the Division’s new
High-Accuracy Cryogenic Radiometer shown in
Figure 13), and SIRCUS, a tunable-laser based
facility for spectral irradiance and radiance
responsivity calibrations of detectors and
radiometers [23]. SIRCUS will significantly
reduce the uncertainties of all of NIST’s
fundamental radiometric and photometric scales.

Figure 13. The Optical Technology Di
second generation High-Accuracy Cryogenic

ion’s

SIRCUS is also being applied to the direct Radiometer (HACR 2). HACR measures the
calibration of various radiometers for absolute power of a laser beam used to
applications in defense, remote sensing, and calibrate silicon trap transfer standard
health and safety. SIRCUS will be a critical tool detectors by comparing thermalized optical

e + . n to th li ‘ical .
for the remote sensing community to realize the Power fo thermalized electrical power

small measurement uncertainties required for
climate-change research [24].

It is also requested that NIST provide leadership in educating the community on determining the
uncertainties of their measurements. This request is a consequence of ISO 17025 quality
standards which require that calibration laboratories state their measurement uncertainty and how
it is derived. The Report suggests that CORM and NIST collaborate in the development of
improved training tools to facilitate the implementation of ISO 17025 by calibration laboratories.
The community has found that the primary reference document, the ISO Guide to the Expression
of Uncertainty in Measurement (GUM), provides insufficient information to enable calibration
scientists and engineers to address the uncertainties in their measurements [25].

NIST recognizes that there is significant demand for training in the area of uncertainty

evaluation. In response, NIST has helped organize several recent meetings such as CORM
Measurement Uncertainty Workshop, May, 2002, in St. Louis; CIE-USA Workshop on

25


Fluorescence plays an important role in the appearance of an object upon illumination, and is
critical in many biophysical measurements, including in single molecule microscopy performed
within the Optical Technology Division and absolute flow cytometry performed within the
Chemical Science and Technology Laboratory (CSTL). The CORM report indicates that there is
an increased need for reference materials in this area and specifically recommends that NIST
undertake the following:

e provide at the national level, a referee measurement service using an accurate two-
monochromator system and including goniometric capability for measurement of the
total radiance and fluorescence of materials. This should include an appropriate
procedure for the calculation of color appearance.

© initiate a measurement assurance program for calibration and testing laboratories to
establish their traceability to NIST and improve their measurement uncertainty.

« provide a series of fluorescent Standard Reference Materials for use by industry and
academia in confirming the adequacy of laboratory measurements.

The Optical Technology Division does not presently have a program in fluorescence standards.
With the addition of a second monochromator, the recently developed reflectance colorimeter
will have the capabilities to measure fluorescent color. Funding for such an effort is presently
being sought. The Division has also collaborated with the CSTL in developing improved
absolute fluorescence measurements for flow cytometry to better assess the number of
fluorescently labeled antibodies bound to a target antigen [21].

0-4 New Standards for Regular Transmittance

The CORM 7" Report requests additional reference materials for an expanded wavelength
region and over a wider range of absorbance. While NIST has a program in this area, the CORM
report asks for it to be expanded through the following recommendations:

© SRM’s be developed with a wide range of absorbance (0.05 - 6 absorbance units in the
visible/UV range, 0.05 - 4 absorbance units in the NIR).

© The overall wavelength range of the standards of high absorbance should be 190 - 850
nm and 850-2,500 nm, respectively. Ideally, standards for transmittance as low as 100
nm should be eventually developed.

Presently, NIST provides measurements of regular transmittance beyond 100 um in the far-
infrared to 250 nm into the ultraviolet. These capabilities are available to NIST customers
through Calibration Service 38061S, Special Test of Spectral Transmittance. Offering these
capabilities through a Calibration Service rather than through a Standard Reference Material
allows the customer to furnish an optical artifact of a material and size appropriate to their needs.
Additionally, the customer is free to specify the wavelength region of interest to minimize costs.
Measurements further into the ultraviolet, to 130 nm, are available using a ultraviolet
spectrometer installed at the Synchrotron Ultraviolet Radiation Facility (SURF II).

21


specific application. CORM and NIST can aid these industry laboratories by working with
standards organizations to initiate the development of appropriate technical standards for the
measurement procedures.

¢ Play a role in reducing measurement uncertainty by education of users. CORM
workshops and/or NIST short courses can be a means to ensure that industry really
understands the techniques for measurement and for uncertainty analysis. NIST
should look at the possibility of using computer based/web-based training media to
meet basic educational needs.

NIST recognizes the need for improved education on the treatment of measurement uncertainty.
The Division’s three short courses offer lectures on measurement uncertainty. We also plan on
working with CORM to develop a full short course, workshop, or web-based training materials
on the evaluation of uncertainty (see section 4).

R-7 Educational Issues of Illuminance

This request was concerned with the special measurement problems that occur with some
modern illumination sources such as LEDs. Specifically the CORM 7 Report suggested the
following:

¢ CORM recommends that a workshop or short course on the measurement of LEDs and
LED lighting should be arranged. Development of a computer-based or web-based
primer or tutorial would be helpful as well.

A lecture on LED measurements has been added to the Photometry Short Course offered
annually at NIST. In addition, NIST has collaborated with other organizations such as CIE to
provide opportunities for discussion of LED measurements. For example, NIST hosted the CIE
2nd Expert Symposium on LED Measurement, May 10-12, 2001 in Gaithersburg, MD, which
included a one day tutorial on LED measurements. NIST also contributed to organizing the CIE
Expert Symposium on LED Light Sources, June 2004 in Japan, which included a number of
papers on LED measurements. We will continue our efforts in providing opportunities for
improved education on LED measurements by working with CORM and other organizations.

R-8 Radiometric and Photometric Issues

This proposal dealt with the changing needs in radiometry and photometry driven by the new
types of light sources being developed and deployed in a wide range of applications. In addition
to LEDs, the widespread use of high-intensity discharge lamps poses new types of design,
application and measurement problems for their effective use. In other applications, researchers
in a wide range of fields from photobiology to remote sensing are using radiometric and
photometric techniques for which standard measurement procedures do not exist. The CORM 7
Report suggests the following for NIST and the community:

« NIST participates and actively contributes to the effective standardization of methods
and procedures used in measurements related to these emerging technologies.


Lamps and Fluorescent Lamps, and of discharge lamps, including high-pressure sodium lamps,
under Special Test Number 371008, Special Photometric Tests. Unfortunately, it is not possible
for NIST to develop capabilities to calibrate the large variety of discharge lamps available
commercially. Potential customers are encouraged to explore the availability of measurement
services for various discharge lamps from commercial calibration and testing laboratories.

To improve industry measurements on non-incandescent sources, NIST is developing total
spectral radiant flux standards [11] to facilitate use of spectroradiometers and thus to avoid the
spectral mismatch error which occurs when a photometer is used to measure a non-incandescent
light source. NIST is also assisting the National Voluntary Laboratory Accreditation Program
(NVLAP) in conducting comparisons of luminous flux measurements of lamp products,
including compact fluorescent lamps, through their Energy Efficient Lighting Products program.
NIST will continue efforts to improve the accuracy of luminous flux measurements of light
sources by industry.

R-2_ New Standards of Luminous Intensity
Specifically the CORM 7" Report made the following observations and suggestions:
e (NIST should) Develop stable reference LEDs for all types of LEDs presently used.

© NIST should offer a calibration service for these reference LEDs using the CIE
recommended (and standardized) measurement conditions.

« New applications are constantly
being developed, and new
reference standards need to be
built and calibrated at NIST as an
ongoing project.

In response to the growing need for LED
measurements and standards, NIST
developed the facilities and calibration
services for LED Averaged Intensity
(Conditions A and B) and total luminous
flux, available through Special Test
Number 371308, Special Tests for
Luminous Inten. and Luminous Flux of
LEDs (see Figure 2). The technical details
of these NIST measurements and
uncertainty budgets are reported [12,13].

Figure 2. A picture of LED color calibration

Through this measurement service, LEDs performed with the ~=LED _ reference
submitted by customers are calibrated for spectroradiometer. The test LED is mounted for the
luminous intensity and luminous flux, with CIE Condition A geometry (baffles around the LED
typical uncertainties of 3 %. Calibrations of have been removed for the photograph).


7. References

. CORM 7" Report: Pressing Problems and Projected National Needs in Optical

Radiometry, (2001).

C. Parr, G. T. Fraser, and K. R. Lykke, “NIST Response to the 6" CORM Report:
Pressing Problems and Projected National Needs in Optical Radiometry,” NIST Internal
Report (NISTIR) 6828 (2001).

General requirements for the competence of testing and calibration laboratories, ISO/IEC
17025, International Organization for Standardization (1999).

A.C. Parr, A National Measurement System for Radiometry, Photometry, and Pyrometry
Based Upon Absolute Detectors, NIST Technical Note 1421 (1996).

M. E. Nadal and E. A. Early, “Recent Developments of the NIST Reference
Colorimeter,” Inter-Society Color Council 2004 Annual Meeting, National Institute of
Standards and Technology, Gaithersburg, MD, May 10-12, 2004.

W. Weber, “Optical Design for Precise Geometry on the New NIST
Goniospectrophotometer,” CORM 2004: A Joint Conference with the Inter-Society Color
Council, Advances in Color and Appearance Metrology, National Institute of Standards
and Technology, Gaithersburg, MD, May 12-14, 2004.

See, for example, CC Miller, T. Heimer, Y Zong, Y Ohno, and G. Dezsi, “Development
of LED Photometric Standards at NIST,” Proc. 25" Session of the CIE, San Diego,
Volume 1, D2 108-111 (2003).

D. W. Allen, Gyula Dezsi, and H. W. Yoon, "Portable LED Illuminated Radiance Source,
" Proceedings of the 9" International Symposium on Temperature and Thermal
Measurements in Industry and Science (TEMPMEKO), Dubrovnik, Croatia, 2004.

H. W. Yoon, David W. Allen, and R. D. Saunders, "Methods to Reduce the Size-of-
Source Effect In Radiation Thermometers," Proceedings of the 9" International
Symposium on Temperature and Thermal Measurements in Industry and Science
(TEMPMEKO), Dubrovnik, Croatia, 2004.

. S.W. Brown, C. Santana, and G.P. Eppeldauer, “Development of a Tunable LED-Based

Colorimetric Source,” Journal of Research of the National Institute of Standards and
Technology, 107, 363-371 (2002).

. Y. Ohno and Y. Zong, NIST Facility for Total Spectral Radiant Flux Calibration, Proc.,

Symposium of Metrology 2004, CENAM, Mexico, Oct. 2004 (published on CD).

28


The categorization and prioritization process that CORM undertakes has increased the interest
and participation of other government agencies in NIST activities. The CORM membership
includes government scientists and engineers and representatives of companies that supply
products and services to such government agencies as NASA, DoD, and DHS. The availability
of documented needs in optical radiation measurement helps managers at these agencies in
ensuring that the funding they provide to the research and development community is optimally
used.

The expanding technical base in the U.S. increases the demand for new and improved technical
support from the national metrology system. It is impossible for NIST alone to respond to all the
measurement needs identified by CORM. By establishing a prioritized list of needs, CORM
helps other government agencies and private organizations to better identify their role and
participation in optical radiation measurement service delivery. In some cases, the report can
serve as a rationale for other government agencies to provide funding to NIST to develop
programs in areas identified in the CORM report that satisfy specific needs of their agency.

The use of optical radiation measurement is pervasive throughout U.S. industry and government.
Industries that use optical radiation measurements include photography, lighting, xerography,
automobile, aerospace, defense, homeland security, instrument manufacturing, chemical, paper,
and printing. The space-based observation systems developed for weather, earth resource, and
agricultural monitoring by National Aeronautics and Space Administration (NASA) and National
Oceanic and Atmospheric Administration (NOAA), and for national defense applications by
Department of Defense (DoD) are critically dependent upon reliable and accurate optical
radiation measurements and standards for their success. CORM is central in defining the optical
measurement and standards needs that this large and diverse community requires, helping to
ensure the continued leadership role of U.S. technology and the global competitiveness of U.S.
industry.

CORM has been a leader in identifying the need for calibration laboratories to adopt appropriate
quality programs. Their efforts, and that of others, have led NIST to adopt an ISO 17025
standard for its measurement services [3]. NIST additionally responded to the need for
measurement quality assurance by expanding the National Voluntary Laboratory Accreditation
Program that serves a wide range of U.S. industry. CORM’s identification of the need for
improved optical power measurement techniques in their early reports helped NIST identify
sources of funding that led to the development and employment of cryogenic radiometers that
now operate with very low levels of measurement uncertainty [4]. The cryogenic radiometer’s
low uncertainty has led to improvement in many of NIST’s optical radiation measurement scales
including photometry, spectral irradiance and radiance, and radiance temperature. CORM’s past
proposals for improved colorimetric standards has given NIST direction and incentive for
establishing new measurement capabilities for reflected color [5,6].

In the present report, the Optical Technology Division’s efforts in addressing the issues raised in
the CORM 7" Report are discussed. For simplicity of presentation and to aid the reader in
comparing the Division’s response to the requests from the CORM 7 Report, the structure of
the CORM 7" Report is followed.


1. Introduction

The CORM 7" report was issued in late 2001 and was circulated to the CORM members and
other interested parties worldwide. Over the years, the CORM reports have generated
considerable interest among managers at government, industry, and university laboratories
because of their ability to anticipate needs in optical radiation measurements. The CORM
reports have served as an important tool for NIST management as some of the identified
requirements and needs are within the mission of NIST. It has become a tradition for NIST to
discuss its efforts to meet the needs identified by CORM in the form of an internal report [2]. It
is the purpose of the present document to discuss NIST’s response to the CORM i Report. The
present response only considers areas within NIST’s mission.

The CORM reports, in addition to defining critical needs, place the needs in a priority order to
facilitate planning. The following explanation of the prioritization process is taken directly from
the CORM 7" Report.

A formal scoring process was followed to evaluate each of the optical radiation proposals. In
evaluating each proposal the following factors were considered:

© Degree of Need: Will the proposed development solve a significant troubling problem
for a large number of users in the optical radiation measurement community?

« Probability of Success: Are we proposing something that we can reasonably expect to
be accomplished?

© Immediacy or Urgency: This category addresses the issue of timing. Will this proposal
solve a problem that is disrupting the optical radiation community right now, or does
the proposal address a problem that can be solved with a longer term, ongoing effort?

¢ Economic Factor: This category addresses the importance of the proposed work with
regard to its impact on US industry, trade or other national priority.

A final overall priority was then assigned based on the average scores received for each
proposal with the following classification in effect:

PRIORITY 1: CORM feels that immediate action is necessary to address the issues in this
proposal.

PRIORITY 2: CORM feels these proposals are important but are not as immediate as the
Priority 1 proposals.

The final prioritized proposals were broken down into the following three categories:
¢ RADIOMETRY
© OPTICAL PROPERTIES OF MATERIALS
¢ MEASUREMENT UNCERTAINTY


Currently, the level of active participation in international discussions on
standardization is appropriate, and this should continue to be the policy of NIST.

« NIST establishes measurement service capabilities in line with such standard methods
and procedures.

e NIST pro-actively seeks to establish standard sources and other artifacts appropriate to
these emerging technologies.

e NIST, CORM and industry provide education and training to users and manufacturers
on appropriate measurement procedures.

NIST is participating in international standards activities on measurements on new types of light
sources, including LEDs, as described above through CIE Technical Committes 2-45, 2-46, and
2-50 and on the photometry of flashing light sources through CIE Technical Committee 2-49 and
ASTM Committee E12.11. NIST also consults with the Optoelectronics Industry Development
Association (OIDA) to better understand measurement and standards needs associated with LED
and organic LED (OLED) source development and commercialization. OLED sources are
typically large flat-area light sources which require unique measurement methods. NIST also
recently started a collaboration with the American Water Works Association Research
Foundation (AwwaRF) to develop standard methods for characterizing and calibrating UV
sensors used to monitor the ultraviolet irradiance (produced by medium pressure mercury lamps)
for disinfecting drinking water in treatment facilities. NIST will continue to keep close contact
with various industrial groups and standards organization to learn about measurement needs
associated with emerging technologies.

3. Optical Properties of Materials

The CORM 7" Report made six proposals for action in the area of optical properties of materials.
There were three priority 1 proposals and three priority 2 proposals that included the traditional
areas of reflectance and transmittance, as well as color and appearance. The proposals are listed
below:

Proposal Identification _ Priority Proposal Title
0-1 1 New Standards for Reflected Color
0-2 1 New Standards for BRDF/BRTF
0-3 1 New Standards for Fluorescence
0-4 2 New Standards for Regular Transmittance
0-5 2 Measurement and Standards for
Retroreflection
0-6 2 Measurement and Standards for Appearance

There has been increased interest in the last decade in the measurement of color and appearance
of products, The CORM 6" Report issued in 1995 had some of the same proposals and NIST
has been able to make progress on some of these areas identified by the CORM reports. We will
discuss the specifics of each proposal in the following sections.


127.2, which expands on the methodology of
luminous flux and __ spectroradiometric
measurements of LEDs. In response to
requests from industry, the latest draft
includes new recommendations — on
integrating sphere geometries for LED
luminous flux measurements and on the
definition of partial LED luminous flux (see
Figure 1). The draft also discusses the use of
spectroradiometers for measuring
photometric and colorimetric quantities, a
practice that is being widely adopted by
industry. The CIE 127.2 draft is still being
finalized by the committee.

NIST also participates in the Project 78
Guide for Measurement of LEDs being
developed by the Testing Procedures
Committee of the Illuminating Engineering
Society of North America (IESNA). This
guide discusses the measurement of LED
clusters and fixtures as well as individual
LEDs. NIST plans to continue working with
industry and national and_ international
standards committees in developing methods
and standards to” — improve ~=LED
measurements to help accelerate the
development and commercialization of solid
state lighting, which promises significant
reductions in energy costs and maintenance.
Recent advances in LED sources have also

Circular Aperture
Diameter= 50 mm

d=—2> [mm] where 0<0<90
tan@

Figure 1. Many applications of LEDs, such as in
traffic lighting and in the backlighting of liquid
crystal displays, require a specification for the
luminous flux in the forward direction, ie. the
partial luminous flux. Currently, the proposed
definition of the partial luminous flux is that it is
the luminous flux transmitted through a 50mm
diameter aperture positioned at a distance d from
the top edge of the LED, thus defining the solid-
angle for the measurement. Measurements are
performed using an integrating sphere with a 50
mm entrance aperture for sampling the light from
the LED, as shown in the lower part of the figure.

motivated NIST to examine their potential as standards for radiometric, photometric, and

colorimetric measurements [7-10].

« NIST should interact with existing laboratories of lamp manufacturers and
independent calibration and testing laboratories to review and comment on methods
and to make comparisons of methods used to arrive at luminous flux values for non-
incandescent, non-LED sources. Participation by NIST in reviewing procedures
including evaluating traceability of the luminous flux level transfer is critical to assure

the confidence of the marketplace.

NIST is a participant in the Lamp Testing Engineers Conference (LTEC) that meets
semiannually to discuss important issues associated with the measurement of the luminous flux
of various types of lamps. NIST has been providing calibrations of fluorescent lamps under
Special Test Number 370608, Special Tests for Total Luminous Flux of Submitted Incandescent


2005. The facility consists of a six-axis goniophotometer mounted on 35-m long rails, a uniform
beam projection system with lighting provided by a tungsten strip lamp, and a photometric
detector system. A “STOP” sign mounted on the goniometer is shown in Figure 11. The facility
is designed to measure both signing materials and road marking materials, and meets all the
geometrical requirements requested by CORM and specified in CIE and ASTM standards. The
details of the NIST measurement facility and uncertainty budget were presented at CORM 2004,
and are described in the final project report submitted to NCHRP [22]. NIST is also leading
efforts in the international standardization of retroreflection measurements through CIE
Technical Committee 2-56, CIE/ISO Standard on Retroreflection Measurements, chaired by C.
Miller of NIST.

The capability for spectral measurement of retroreflectance was not included in the NCHRP
project mentioned above. However, NIST plans to expand the facility to enable spectral and
color measurements of retroreflective materials excluding fluorescent material. The equipment
required for this capability has been purchased with NCHRP support.

As part of the NCHRP project, NIST is re-establishing the retroreflectance Measurement
Assurance Program. NIST is in the process of obtaining the standard materials required for this
program and assessing their temporal stability. The Measurement Assurance Program provides a
mechanism for testing laboratories to participate in bi-lateral comparisons with NIST using NIST
provided materials. NIST is also working with the National Voluntary Laboratory Accreditation
Program (NVLAP) to develop an accreditation program for calibration laboratories.

0-6 Measurement and Standards for Appearance

The development of new paints and coatings with complex angular-dependent visual effects,
such as metallic and pearlescent coatings whose appearance depends upon both viewing and
illumination angles, is challenging the ability of industry to characterize and quantify product
appearance. The increased globalization of manufacturing and its supply chain requires
improved international standards for color and appearance to ensure that product appearance can
be correctly specified and realized independent of locale. The importance of product appearance
in nearly all commercial transactions motivates NIST and other national metrology institutes
efforts to develop standards in this area. The CORM 7" Report likewise recognizes the
importance of appearance metrology, recommending that NIST do the following:

© Continue and complete the “Optical Reflectance and Scattering of Materials Project”.

The Division’s Color and Appearance Program was initiated by the successful NIST Director’s
Competence Program in Measurement Science for Optical Reflectance and Scattering. This
program led to the development of calibration services for specular gloss using the instrument
shown in Figure 12 and for reflected color in the 0/45° geometry using the instrument shown in
Figure 9. A calibration service for diffuse reflected color is also under development. The
expertise developed through this competence program spawned new research, funded by the
NIST Advanced Technology Program, into the colorimetric characterization of special-effect
coatings, particularly pearlescent coatings. This research determined a subset of optimal
measurement angles for accurately characterizing the coatings.

23


NISTIR 7194

NIST Response to the 7" CORM Report:
Pressing Problems and Projected National
Needs in Optical Radiation Measurement

Albert C. Parr
Gerald T. Fraser
Yoshi Ohno

NUT

National Institute of Standards and Technology
Technology Administration, U.S. Department of Commerce



| Displays, to provide _ state-of-the-art
uncertainties for display color
measurements [14]. This service allows
customers to submit for calibration

colorimeters or luminance meters used for
measurements on LCD and other displays.
Since the instruments are directly calibrated
against an LCD display, the effects of
polarization are accounted for in the
measurements. Surprisingly, this service
has had no customers since it was
established in 2001, although several price
quotations were provided. The quoted fees
were only slightly higher than the fees for
illuminance meter calibrations. The reason
for this apparent lack of interest in the
service is not clear, but may be due to poor

Figure 3. Integrating sphere source instrumented
with a number of LEDs with currents individually
controlled. Sample outputs from the source are
illustrated in the upper left hand corner of the

marketing of the service to potential figure. The source is being developed as a spectrally
customers. The related Display _‘tumable radiance standard [10].
Measurement Assessment Transfer

Standard (DMATS) program within the Optoelectronics Division is still under development.
Related to this, NIST is developing a spectrally-tunable standard source for general radiometric
which can be used for calibration of colorimeters and luminance

meters for display

2. Communication of NIST services to the measurement community should be increased.
The indicated measurement services by NIST already exist. Many respondents in other
areas of concern indicated a need for services that are already offered by NIST. It is
apparent that information on some services offered are not adequately communicated
to those needing them. CORM should aid NIST in making such information more
widely available.

NIST has published a number of papers directed at the display community [14], and has
publicized the availability of the service at technical meetings. Additionally, NIST offers an
annual Photometry Short Course with approximately 30 attendees, as well as short courses in
Radiation Temperature and Spectroradiometry, as discussed in Figure 4, providing attendees
with information about NIST’s calibration services in photometry, colorimetry, and radiometry.
Despite these efforts, NIST and CORM need to work to further improve communication about
NIST calibration services to potential industry customers through improved web information and
tutorial articles in trade journal and magazines.


LED color and UV radiant flux are being established. NIST is also investigating various LEDs
to assess their suitability as transfer standards for radiometric, photometric, and colormetric
measurements. [7-10].

It is difficult for NIST to prepare standards for all types of LEDs in use, especially when the
LED technology is so rapidly changing. The needs for various types of LED standards are
fulfilled in part by the current calibration services since they allow users to submit an LED for
test. NIST will continue efforts to study new LED sources to ensure the currency of its
measurement and calibration programs.

© Workshops and tutorials need to be organized to introduce the measurement principles
and uncertainty evaluation methods to those professionals who are new to this type of
optical measurement.

NIST has been offering a Photometry Short Course since 1998. The course includes lectures on
LED measurements with discussion of the measurement uncertainty. We recognize the need for
more focused training on uncertainty evaluation, and NIST plans to develop a separate short
course on this subject in the near future. See section 4 for further discussion.

R-3 New Standards and Definitions for Luminance

The respondents to the CORM 7 Report outlined three measurement areas of concern in
luminance:

1. LCD displays are highly polarized. Calibration with relatively unpolarized sources may
give significant errors when applied to the displays.

2. A calibration service, offered by NIST, for the calibration of luminance meters and
calculation of correction factors was requested.

3. Road signals often utilize discrete devices such as LEDs. Typical characterization of
these displays are in terms of luminance vs angle. However, being highly non-uniform
in emission, no satisfactory definition of luminance that applies to both near-field and
far-field viewing conditions exists.

To address these concerns the CORM 7" Report provided three recommendations:

I. A luminance standard, possibly incorporating an LCD panel, be investigated. This
might be part of, or independent from, the current DMATS program. The aim is to
allow calibrations to be used directly for LCD or similar displays without the need for
compensations for the polarization differences between standard and display.

Based on earlier recommendations by CORM and knowledge of industry’s needs, NIST
established calibration service 37120S, Special Tests for Color Measuring Instruments for

{ Deleted: as illustrated in Figure 3


23. S. W. Brown, G. P. Eppeldauer, J. P. Rice, J. Zhang, K. R. Lykke, Spectral Irradiance and
Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) Facility at NIST,
Proceedings of the SPIE 5542, 363-374 (2004).

24. Satellite Instrument Calibration for Measuring Global Climate Change, (Report of a
Workshop at the University of Maryland Inn and Conference Center, College Park, MD,
November 12-14, 2002), Edited by G. Ohring, B. Wielicki, R. Spencer, B. Emery, and R.
Datla, NIST Internal Report (NISTIR) No. 7047, March 2004.

25. Guide to the Expression of Uncertainty in Measurement, International Organization for
Standardization, 1995.

30


12.

20.

2

22.

C. C. Miller and Y. Ohno, Luminous Intensity Measurements of Light Emitting Diodes at
NIST, Proc. 2"! CIE Expert Symposium on LED Measurement, May 11-12, 2001,
Gaithersburg, Maryland, USA, 28-32 (2001).

. C. C. Miller and Y. Ohno, Luminous Flux Calibration of LEDs at NIST, Proc. 2" CIE

Expert Symposium on LED Measurement, May 11-12, 2001, Gaithersburg, Maryland,
USA, 45-48 (2001).

. See, for example, F. Manoocheri, S. W. Brown, and Y. Ohno, NIST Colorimetric

Calibration Facility for Displays — Part 2, Society for Information Displays ‘01 DIGEST,
330-333 (2001).

. A.V. Murthy, B.K. Tsai, and R.D. Saunders, “NIST Radiative Heat Flux Sensor

Calibration Facilities and Techniques,” Journal of Research of the National Institute of
Standards and Technology 105, 293-305 (2000).

. H.W. Yoon, J.E. Proctor, and C.E. Gibson, “FASCAL 2: A New NIST Facility for the

Calibration of the Spectral Irradiance of Sources,” Metrologia 40, S30-S34 (2003).

. P.-S. Shaw, U. Arp, H. W. Yoon, R. D. Saunders, A. C. Parr, and K. R. Lykke, “A SURF

Beamline for Synchrotron Source-Based Absolute Radiometry,” Metrologia 40, S124
(2003).

. D. W. Allen, R.D. Saunders, B.C. Johnson, C.E. Gibson, and H.W. Yoon, “The

Development and Characterization of an Absolute Pyrometer Calibrated for Radiance
Responsivity,” in TEMPERATURE: Its Measurement and Control in Science and
Industry, Volume VII; Eighth Temperature Symposium, Chicago, Illinois (USA),
October 2002, available from AJP Conference Proceedings 684, 577-582 (2003).

. J.P. Rice, K.R. Lykke, H.W. Yoon, "A method for testing the spectral responsivity of

infrared cameras using tunable lasers," in Infrared Imaging Systems: Design, Analysis,
Modeling, and Testing XIV, Edited by G.C. Holst, Proceedings of the SPIE 5076, 112-
122 (2003).

. E.A. Early and M.E. Nadal, “Uncertainty Analysis for Reflectance Colorimetry,” Color

Research and Application 29, 205-216 (2004).

. G.E. Marti, A. Schwartz, R.F. Vogt, A. Zhang, A.K. Gaigalas, L. Wang, E. A. Early,

“Quantitating Fluorescence Intensity from Fluorophore: The Definition of MESF
Assignment,” Journal of Research of the National Institute of Standards and Technology
107, 83-91 (2002).

C.C. Miller, T. Heimer, and E. Early, “National Calibration Facility for Retroreflective

Traffic Control Materials — Phase II,” Final Report for NCHRP 05-16 Project, available
through NCHRP.

29


2. Radiometry

The CORM 7" Report had eight proposals under the heading of radiometry. Of these, R-1 and
R-2 were deemed to be of priority 1 and the rest priority 2.

Proposal Identification _ Priority Proposal Title

R-1 1 New Standards of Luminous Flux

R2 1 New Standards of Luminous Intensity

R-3 2 New Standards and Definitions for
Luminance

R-4 2 New Standards of Spectral Irradiance

R-5 2 New Standards of Spectral Radiant Flux

R-6 2 Improvements to Goniophotometry and
Gonioradiometry

R-7 2 Educational Issues of [luminance

R-8 2 Radiometric and Photometric Issues

R-1 and R-2 address the need for improved standards for light emitting diodes or LEDs, devices
expected to furnish the foundation for future solid-state lighting. Priority R-3 is concerned with
luminance issues associated with LEDs and liquid-crystal displays (LCDs). The radiometry
proposals are discussed in order below.

R-1 New Standards of Luminous Flux
Specifically the CORM report recommended that

e NIST develop standard methods and evaluate calibration artifacts for their suitability
for the determination of the luminous flux from LED sources. This should incorporate
internationally accepted definitions related to LED source characteristics. It is
necessary to develop methods of measurement for LEDs that result in the measurement
of the basic physical quantities associated with light sources so that intercomparison of
all sources is facile for specifiers and lighting designers and for federal and state
regulators involved in the assurance of energy efficiency claims for light sources.

¢ NIST should continue its involvement in the development of international standards
for evaluation of luminous flux for practical light sources of all types. This means
primarily involvement in CIE division activities. Presently NIST participation is very
active and very productive on behalf of US interests. The level of participation is
appropriate and should continue to be supported.

NIST has been collaborating with a number of organizations to develop and improve methods for
measuring the properties of LEDs and other light sources. NIST is working with CIE Technical
Committee 2-45, Measurement of LEDs—Revision of CIE 127, to improve luminous flux
measurements of LED sources. NIST contributed extensively to the latest draft (Draft 4) of CIE


this area and provides calibration services, there is a continual new demand for reference
materials. This is reflected in the CORM 7" Report which recommends that

Standard Reference Materials (SRM’s) be developed for bi-directional reflectance
distribution factor (BRDF), both of nominally high and low reflectance for both high
and low scatter samples covering the wavelength range from the UV to the mid-IR
(approx. 190 - 25,000 nm). These standards should have minimal reflectance structure
(and thus a series of standards, each with different spectral reflectivity, should be
considered) in the area of interest. In the absence of SRM’s, a measurement service to
allow customers to obtain NIST-certified values for customer supplied materials would
be an acceptable alternative.

© SRM’s be developed for bi-directional transmittance distribution factor (BTDF), both
of high and low nominal transmittance and with both high and low degrees of forward
scatter. Such standards need not cover as wide a spectral range as the BRDF SRM’s,
but should be usable over a fairly wide range in the UV-VIS-NIR (190-2500 nm).
Again, in the absence of SRM’s, measurement services on customer-supplied samples
would be an acceptable alternative.

e NIST work with U.S. industry, military and
NASA to develop and maintain SRM’s for
these measurement techniques.

NIST has extensive capabilities for measuring the
BRDF and BRTF of materials, including STARR
shown in Figure 10. These capabilities extend from
the infrared to the ultraviolet and are available to NIST
customers through NIST Calibration Service Special
Tests 38060S and 38061S. Because of the varied
needs of NIST customers for specific measurement
wavelengths and angles and material size and
composition, the Division has not made these
capabilities available through Standard Reference
Materials (SRMs). NIST is willing to work with U.S.
industry, military, and NASA to improve BRDF and
BRTF measurements and standards. Indeed, NIST has
had ongoing collaborations in BRDF measurements

Figure 10. A picture of STARR, the

with the semiconductor industry for wafer inspection Spectral Tri-function Automated
and with the remote-sensing community for realizing a Reference Reflectometer, used to
spectral radiance scale from illumination of a measure in-plane BRDF.

Spectralon plaque with an FEL lamp spectral
irradiance source. Partners in other areas of remote
sensing, defense, and homeland security are welcome.

0-3 New Standards for Fluorescence

20


Uncertainty in Lighting Measurements, November, 2001, in Niagara Falls; and CIE Expert
Symposium on Uncertainty Evaluation, January, 2001, in Austria to provide improved training
and discussion opportunities. NIST also provides a lecture on uncertainty evaluation coupled
with a laboratory session in the NIST Photometry Short Course since 1998. While these
meetings and courses have been successful, the CORM ye report suggests growing demand for
education on this subject. NIST will work together with CORM to explore the possibility of
offering a tutorial workshop or short course on uncertainty evaluation directed towards scientists
and engineers striving to implement ISO17025. The possibility of disseminating such training
electronically will also be explored.

5. Conclusions

Over the past four years, the Optical Technology Division has successfully addressed many of
the high-priority recommendations in the CORM 7 report. This success has been aided by
improvements in the accuracy of NIST’s radiometric and photometric measurements made
possible by SIRCUS. SIRCUS has improved the Division’s ability to replace its source-based
radiometric scales with detector-based scales directly tied to the cryogenic radiometer. In
addition, SIRCUS, its infrared implementation, IR-SIRCUS, and its transportable version,
Traveling SIRCUS, have improved the Division’s ability to respond to DoD, NOAA, and
NASA’s needs for improved instrument characterization and calibration in support of national
priorities in climate-change research and missile defense.

The CORM reports have also aided the Division in ensuring that its programs are current with
changing industry needs. Examples include CORM requests for improved measurements and
standards for LEDs and for color and appearance. Both of these requests have led to significant
NIST efforts in developing new measurement facilities directly addressing needs in these areas.
Measurements and standards provided by these facilities are accelerating the development and
commercialization of solid-state lighting and aiding electronic commerce and _ global
manufacturing.

The CORM 8" report is due to be released in the near future and we look forward to studying its
recommendations to gain guidance on future opportunities for NIST programs. We view this
response to a CORM 7" report as an essential mechanism to complete the cycle of
recommendation, evaluation, action, and assessment and we are hopeful the optical radiation
measurement community finds our response useful. The authors thank the staff of the Optical
Technology Division for assisting in the writing of this report by furnishing updates on their
projects.

6. Acronyms

Below is a list of common acronyms used in the radiometric and photometric literature,
including this report:

ANSI American National Standards Institute
BIPM Bureau International des Poids et Mesures

26


Contents
Preface
1. Introduction
2. Radiometry
3. Optical Properties of Materials
4. Measurement Uncertainty
5. Conclusions
6. Acronyms

7. References

i)

17

24

26

26

28


course consists of a week of lectures and laboratories to help educate students in the
measurement of optical radiation. In October of 2004 the Division offered a lecture-only short
course at the Night Vision and Electronic Sensors Directorate (NVESD) at Fort Belvoir, VA,
combining selected topics from the Photometry, Radiance Temperature, and Spectroradiometry
Short Courses, with additional topics tailored to the needs of the NVESD. More than 60
contractors and staff members from NVESD attended.

To ensure that NIST customers have access to spectral irradiance standards with the lowest
measurement uncertainties, the Optical Technology Division has recently completed the
development of a new Facility for Spectroradiometric Calibrations (FASCAL 2) for
disseminating spectral irradiance FEL lamp standards [16]. This facility replaces the aging
FASCAL facility which has successfully provided NIST customers with spectral irradiance
calibrations for some thirty years. This facility will lower the uncertainties of NIST’s
disseminated scale, particularly in the near infrared, to allow customers to realize the full
advantage of NIST’s new detector-based spectral irradiance scale traceable to the electrical watt
through the cryogenic radiometer.

In addition to improving its scale dissemination, NIST is continually advancing its spectral
irradiance and radiance scales. Recent activities include the following:

¢ The implementation at the Synchrotron Ultraviolet Radiation Facility (SURF III) of new
capabilities for calibrating the spectral irradiance of deuterium arc lamps between 200 nm
and 400 nm using SURF as an absolute source [17] (see Figure 6).

« The development of new absolute pyrometers
calibrated at SIRCUS for improving the
determination of the — thermodynamic
temperature of high-temperature fixed-points
important in the realization of the ITS-90
temperature scale. Such pyrometers will
allow NIST to make the move from source-
based to detector-based scales for spectral
radiance and radiance temperature [18].

e The move of the SIRCUS, Aperture Area
Measurement, and High Accuracy Cryogenic
Radiometer 2 facilities to the new Advanced
Measurement Laboratory to improve the
quality of the measurement environment
through lower particulates, better temperature
and humidity control, and reduced vibration

necessary {0 ensure the most accurate Fisure 6, Synchrotron radiation from SURF
realization of the Division’s radiometric and gy yi t! ‘

1 ; 1 wed through a glass viewport at the
photometric scales which are ultimately all end-station of the beamline 3. This beamline
dependent on these three facilities. is used to realize a spectral irradiance scale

from 200 nm to 400 nm for the calibration of
deuterium arc lamps [17].

13


radiant flux standards are also
required for color measurements of
light sources placed in integrating

Stepping
spheres. mole

Spectro-
radiometer

Servo
The total spectral radiant flux scale
is being realized at NIST from 360
nm to 800 nm region with a target
uncertainty of 1 % (k=2). Two
independent methods are under
development, a
goniospectroradiometric method
and an absolute integrating sphere
method. The scales realized from
the two methods will be used to
verify the scale uncertainties. The
NIST  goniospectroradiometer is
illustrated in Figure 8. Total
spectral radiant flux standards based Figure 8. Design of the NIST goniospectroradiometer.
upon 1000 W FEL tungsten halogen
lamps (mounted on a screw base) will be available in 2005, and for lower power lamps for use in
smaller integrating spheres (e.g., for LED measurements) somewhat later. Future plans include
expanding the scale into the ultraviolet and infrared. Further details are available in reference

{11}.

Irradiance
head

R-6 Improvements to Goniophotometry and Gonioradiometry

CORM has also identified needs in characterizing the angular distribution of radiation from
illumination and other types of light sources such as lamps, LEDs, and electronic displays. In
particular, the CORM 7" Report identifies the following needs:

* Develop new or improved standard procedures for measuring extended sources. These
could positively impact the measurement uncertainty.

e Provide better analysis and simulation tools to model a given measurement. Software
simulation tools could serve as a possible alternative to developing and maintaining
expensive standards or as a tool to calculate measurement uncertainty.

The Optical Technology Division has not addressed the goniometric characterization of general
light sources, although goniometric measurements are performed on standard lamps and LEDs
used at NIST. Goniophotometry measurements of luminaries has been well established through
standards developed by IESNA and by calibration services provided by commercial testing
laboratories. | Measurements on electronic displays are available from the Optoelectronics
Division. Procedures for the goniophotometric measurement of extended sources are highly
application dependent, and better addressed by industry laboratories knowledgeable about the

1S


Abstract

The Council for Optical Radiation Measurements (CORM) issues periodic reports
relevant to the mission of the Optical Technology Division of the Physics
Laboratory. The present document summarizes NIST’s response to the CORM
Seventh Report issued in 2001 and is timed to be contemporary with the CORM
Eighth Report to be issued in 2005.

Key Words: colorimetry, metrology, optical properties of materials, optical
radiation, photometry, radiometry, spectroradiometry


=
*
:
.

— i

Figure 12. The NIST Specular Gloss instrument. Specular gloss standards are available
from the Optical Technology Division through a calibration service.

e Establish a laboratory program directed toward appearance measurement, this effort
should include research into the human factors affecting visual evaluations so that the
importance of these attributes is understood.

| Due to a lack of expertise in psychophysical research, NIST has not addressed the issue of
human factors in appearance attributes. The Optical Technology Division is willing to partner
with universities, government, or industry in research into such human factors by furnishing the
appropriate physical measurements.

° Develop a system of SRM's on gloss, haze, contrast, texture, translucency, and other
appearance attributes that can be disseminated to user laboratories. Where scales
appear for such attributes, the emphasis should be upon visual interval scaling.

Instrumentation development efforts for color and appearance measurements have continued
since the completion of the Measurement Science for Optical Reflectance and Scattering
Competence Program. Implementation of full goniometric capabilities on the NIST Colorimeter
now in progress will allow reflected color measurements as a function of illumination and
detection angles, a critical capability for characterizing special-effect pigment coatings. It is
anticipated that such research capabilities will lead to new NIST standards for haze, contrast,
texture, translucency, and other appearance attributes to be distributed through Calibration
Services rather than through SRMs to provide flexibility to meet specific customer needs.

4. Measurement Uncertainty

There was only one proposal in the category of measurement uncertainty:

24

- (Deleted: psychology


NISTIR 7194

NIST Response to the 7 CORM Report:
Pressing Problems and Projected National
Needs in Optical Radiation Measurement

Albert C. Parr
Gerald T. Fraser
Yoshi Ohno

January 2005

tor
yw

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yn * dg,
oo”
%,

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STares oF

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

TECHNOLOGY ADMINISTRATION

Phillip J. Bond, Under Secretary of Commerce for Technology
NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY
Arden L. Bement, Jr., Director


BRDF
BTDF
CCPR
CFR
CIE
CORM
CRT
DHS
DoD
EOS
HACR
IEC
IESNA
ILAC
IR

ISO
JCRB
LCD
LED
MAP
MOU
MRA
NASA
NHCRP
NIR
NIST
NMI
NOAA
NVLAP
OIDA
OSA

SIRCUS

SPIE
SRM
STARR
SURF

VESA
Vis

Bi-directional Reflectance Distribution Function

Bi-directional Transmittance Distribution Function

Consultative Committee for Photometry and Radiometry

Code of Federal Regulations

Commission Internationale de LEclairage

Council for Optical Radiation Measurements

Cathode ray tubes

Department of Homeland Security

Department of Defense

Earth Observing System

High Accuracy Cryogenic Radiometer

International Electrotechnical Commission

Illuminating Engineering Society of North America

International Laboratory Accreditation Council

Infrared

International Standards Organization

Joint Committee of the Regional Metrology Organizations and the BIPM

Liquid crystal display

Light emitting diode

Measurement Assurance Program

Memorandum of Understanding

Mutual Recognition Arrangement

National Aeronautics and Space Administration

National Highway Cooperative Research Program

Near Infrared

National Institute of Standards and Technology

National Measurement Institute

National Oceanic and Atmospheric Administration

National Voluntary Laboratory Accreditation Program

Optoelectronics Industry Development Association

Optical Society of America

International System of Units

Spectral Irradiance and Radiance responsivity Calibrations using Uniform
Sources

NIST special publication

The International Society for Optical Engineering

Standard Reference Material

Spectral Tri-function Automated Reference Reflectometer

Synchrotron Ultraviolet Research Facility

Ultraviolet

Video Electronics Standards Association

Visible

27


I

Figure 4. Logos for the Optical Technology Division's Photometry, Spectroradiometry, and
Radiation Temperature Short Courses. These week-long short courses typically offered annually,
provide attendees with a series of lecture and laboratory sessions which demonstrate fundamental
and advanced concepts in photometry, spectroradiometry, or radiation temperature. The courses
also provide Division scientists and engineers with opportunities to learn more about the needs of
the attendees in the areas of photometric measurements and standards.

3. NIST and industry should collaborate to provide an adequate definition of luminance,
as applied to discrete LED signage. Sources to test and calibrate instruments to this
definition would also be needed.

The definition of luminance for LED signage requires an improved understanding of the human
factors involved in assessing the visibility of LED-based signs relative to conventional head-light
illuminated signs. NIST currently does not have the resources or expertise to conduct such
research. NIST is, however, participating in discussions with standardizing bodies such as the
CIE (Technical Committee TC2-50, Measurement of the Optical Properties of LED Clusters and
Arrays) and the IESNA (Testing Procedures Committee Project 78) to develop standards in this
area.

R-4 New Standards of Spectral Irradiance

Improved and more reliable spectral irradiance standards from the vacuum ultraviolet to the far
infrared have been requested in most of the past CORM reports. While there has been
considerable progress in the past decade in this area, the CORM vi Report makes the following
additional suggestions:


¢ Near completion of the IR-SIRCUS facility, which will allow the infrared radiometry
community to realize the benefit of absolute tunable-laser-illuminated integrating sphere
sources for spectroradiometric calibrations [19] (see Figure 7).

0.14 ;
0.12 4 A
0.10 ,
0.08
0.06
0.04

SH ak ae

y
£
i
b:
0.02

4204 smn Nnseue

41 42 43 44 45 46 47 48 49 5.0
Wavelength / um

Irradiance Responsivity / [V/(uW/cm’)]

Figure 7. Absolute irradiance responsivity measurement of an infrared radiometer performed
on the IR-SIRCUS facility. The relative measurement uncertainty is 1.5% (k = 2).

R-5 New Standards of Spectral Radiant Flux

Spectral radiant flux measurements provide the spatially-integrated spectral distribution of light
sources such incandescent, fluorescent and discharge lamps used in a variety of applications,
particularly for lighting. Advances in LED and other solid-state lighting sources are generating
new interest in spectral radiant flux measurements. The CORM ge Report identified the
following two needs for spectral radiant flux measurements:

« NIST develops methods for calibration of spectral radiant flux of light sources.
Combined standard uncertainties should be 1% or better over the wavelength range
from 360 nm to 800 nm. Uncertainty due to source instability should be separately
listed in the uncertainty budgets to allow for reduction of uncertainty by repeated
measurements by the end user.

¢ NIST should work with industry organizations to develop artifacts capable of achieving
the target uncertainties.

The Division has nearly completed the realization of the total spectral radiant flux scale to be
disseminated by FEL lamps. The availability of total flux measurements as a function of
wavelength will eliminate problems associated with the spectral mismatch of photometers when
used to measure non-incandescent light sources, such as single-color LEDs. Total spectral

14