The A*STAR’s National Metrology Centre (NMC) is the national measurement institute of Singapore, dedicated to advancing measurement science for an innovative and competitive economy
NMC establishes, develops, maintains and disseminates the national measurement standards traceable to the International System of Units, providing key support to a wide spectrum of industry.
Achieving the nation’s highest level of physical measurement through close collaboration with leading national and international organisation.
With a multidisciplinary team of experienced scientists and engineers and state-of-the-art facilities, NMC provides dedicated services to industry partners to meet their specific needs.
NMC believes in working in close collaboration with industry partners, to create values for them and fuel growth for the industry.
LEDs are increasingly being used as general illumination sources due
to their high efficacy and durability. But do LEDs provide high quality
lighting? Two important measurements of lighting quality are:
Chromaticity of light (whether the light appears warmer/cooler or
greenish/pinkish) and Colour rendering (the ability of the lighting to
render colours of the objects under its illumination).
Chromaticity of light is measured by chromaticity coordinates or by
correlated colour temperature (CCT, unit: kelvin [K]) and the distance
from the Planckian locus (Duv). For most interior lighting applications,
warm white (2700K to 3000K) and neutral white (3500K to 4000K) light
are typical in European countries and USA. Higher CCT (5000 K to 7000 K)
tends to be preferred in Asia. Some lightings use cool-white LEDs with
very high CCT (more than 6500K, bluish in appearance) since the current
white LEDs tend to offer higher efficacy at lower cost at higher CCT.
Colour rendering property is normally measured using colour rendering
index (CRI). CRI is a quantitatively measurable index of the quality of a
light. A perfect broadband light like an incandescent light bulb or the
day light from the Sun has a CRI value of 100. Although the CRI has
been found to be problematic for RGB (red, green, blue) and narrow-band
LED systems, it remains the standard method for colour rendering
property evaluation of general lighting including LED lights. The
National Institute of Standards and Technology (NIST), USA has developed
a Colour Quality Scale (CQS) that is intended to replace or supplement
the current CRI. CQS is designed to solve the problems of CRI and to
provide the scores that correlate well with perceived colour rendering.
NMC is organising this seminar focusing on LED colour and colour
rendering. Dr Yoshi Ohno, the developer of CQS at NIST, USA, has been
invited to give a presentation on "LED colour and colour rendering
properties measurement and relevant standards". Dr Ohno is a NIST Fellow
and has been the Group Leader for Lighting and Colour Group, NIST, USA,
and also serves as the CIE Vice President Technical. His group
maintains the national standards of the lumen, candela, and other
photometric units and colorimetric scales for USA, and developed the
CQS. The seminar will be relevant to technical staff working in the LED
industry who would like to learn about colour and colour rendering
properties measurement of LED lightings. The seminar also provides an
excellent platform for participants to discuss technology and
application issues faced by the local LED community.
Welcome and Opening Address
LED Colour and Colour Rendering Properties Measurement and Relevant Standards
Dr Yoshi Ohno, NIST Fellow and the Group Leader for Lighting and Colour Group,
National Institute of Standards and Technology (NIST), USA
Colour quality of lighting has two aspects, the chromaticity of
light and the colour rendering. Chromaticity is often expressed by
correlated colour temperature (CCT) but it is only one of the dimensions
of chromaticity. Another important dimension is the distance from
Planckian locus (defined as Duv in USA), which is often neglected. We
will discuss the importance of Duv and its important effects in
perceived colour quality in relation to the ANSI C78.377 standard. We
will then look at the problems of the CRI for LED sources and how Colour
Quality Scale (CQS) can improve the evaluation and design of colour
quality of SSL products. Some results of vision experiments using NIST
Spectrally Tunable Lighting Facility will be presented and status of the
CIE work will be reported.
LED/SSL Photometry and Radiometry Facilities at NMC
Mr Liu Yuanjie, Assistant Head (Optical Metrology) and Senior Metrologist
National Metrology Centre
LEDs are increasingly being used as general illumination sources
due to their high efficiency and durability. The lighting principle of
LED is different from traditional light sources such as incandescent
light bulb and fluorescent tubes. The optical measurements of these
light sources are more difficult than others. Several types of light
measurements are applicable to LEDs, which can be possibly achieved by
different measurement technologies. For instance, the total luminous
flux of a LED lamp can be measured by means of an integrating sphere
photometer calibrated by a total flux standard lamp, or alternatively by
a goniometer with its detector calibrated using a spectral irradiance
standard lamp. This presentation will cover LED measurement technologies
and facilities currently available at NMC. The key factors affecting
the measurement accuracy of LED lights and proper correction methods for
these factors are discussed. Developments for new measurement
facilities are also introduced.
About the Speakers
Dr Yoshi Ohno, NIST Fellow and the Group Leader for Lighting and Colour Group, NIST, USA
Dr Yoshi Ohno is a NIST Fellow and the Group Leader for Lighting and
Colour Group at Sensor Science Division, National Institute of Standards
and Technology, USA. His group maintains the national standards of the
lumen, candela, and other photometric units and colorimetric scales for
USA. He received his Ph.D. in engineering from Kyoto University, Japan.
He started his career at Panasonic Corp., Osaka Japan before joining
NIST in 1992. Dr Yoshi Ohno is actively involved in research of
photometry and colorimetry. Specific projects of interest include
integrating sphere theory, luminous flux measurement, colorimetry of
light sources, colour rendering, spectroradiometry, photometry of
flashing lights, and solid state lighting. He served as Director of CIE
Division 2 for 2007-2011, and currently serves as CIE Vice President
Technical. He is a Fellow of IESNA, NIST representative for CCPR, Chair
of CCPR Working Group of Key Comparisons, and is active in technical
committees in CIE, ISO, ANSI, and IESNA. Dr Ohno received several awards
including the CIE de Boer Gold Pin Distinguished Service Award in 2007
and U.S. Department of Commerce Silver Medal Award in 2009.
Mr Liu Yuanjie, Assistant Head (Optical Metrology) & Senior Metrologist, National Metrology Centre
Mr Liu is a Senior Metrologist in the Optical Radiation Lab of
National Metrology Centre (NMC). His expertise includes development and
application of measurement technologies and standards for the
photometry, spectroradiometry, spectrophotometry and colorimetry. Since
joining NMC in 1998, he has developed the NMC Reference
Spectrophptometer for spectral regular transmittance measurement, a
Spectral Irradiance Calibration Facility, an Automatic Multi-Wavelength
Filter Radiometer (MWFR) for the realisation of a detector-based
spectral irradiance measurement scale, CIE averaged LED Intensity
Measurement Facility and LED Total and Forward Flux Measurement
Who Should Attend
Researchers, engineers, designers and manufacturers, system
integrators, purchasers and contractors, students and users of LEDs and
lighting systems, from universities, research institutes and industry
should find the topics useful and informative, as well as anyone
interested in LED lighting in general.
National Metrology Centre
1 Science Park Drive
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F: +65 6279 1992/1993
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