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Interview : Energy-saving policy and standard research for solid-state lighting in the United States−167−Synthesiology - English edition Vol.2 No.2 (2009) actively, and took the leading role in some parts. No standard, no recommendation (Ono)So NIST is cooperating in the creation of not only metrology standards, but also industrial standards? (Ohno)Yes. I talked about quality earlier. For example, talking about the chromaticity of a lighting source, people dislike lighting when the overall appearance gives a yellowish or greenish hue and this is a cause for products to be returned. Since this was a very important issue, a task group to create a standard for chromaticity for SSL light sources was set up in the American National Standards Institute (ANSI). I became the leader to develop the standard. (Ono)As a matter of perception, I don’t want to be in a yellow room, and a green room is unsettling. A red or blue room would be more acceptable. (Ohno)Yes. We wanted to define that, and establish it as an industrial standard, and ensure good color quality of products through Energy Star.For measurement, the Illuminating Engineering Society of North America (IESNA) published a document (LM-79), which is a standard for the testing method used as a reference by the Energy Star. I also led this standardization project. For example, it sets standards for how to measure the luminous flux using the unit lumen, how to arrange the integrating sphere, and what kind of detector should be used. There are two types of integrating spheres: one using a photometer and the other using a spectroradiometer. The accuracy for industrial use is much higher when the spectroradiometer is used. But, in order to use a spectroradiometer, a metrology standard for the spectral radiant flux will be needed. NIST has been working on this standard for several years and has made it available, which is one of the key points in this standard.If you want to recommend this method, you must have a metrology standard required in the method. Unless you have that standard available, you cannot just put that method down in a document and say, “Please use this method.”(Ono)The importance of spectral radiant flux measurement has been also recognized at AIST, and we just started working in that direction. Do we get high quality product by raising the assessment values? (Ohno)There’s another point concerning the quality of a LED light source. When assessing the color rendering of a lighting source, there is an index called the CRI (color rendering index). This index has a full scale value of 100. 80 points or higher is recommended for interior lighting. This index was created about 40 years ago for fluorescent lamps. However, using my simulation program, it was found that there were many problems when this index was applied to LED light sources.When the spectrum of the output light is focused to the center of the visible range, the efficiency of the luminous flux value (lumen/watt) will increase, while, in general, color rendering decreases. Companies are competing with each other over the value of lumen/watt. However, it was found by my simulations that if they seek for a spectrum with the highest lumen/watt, for example, at a CRI of 80, the appearance of the light will have an unacceptable poor red color. A LED light source can become unusable for interior lighting even if it has a CRI number of 80 (Fig. 1).Also, it is possible to raise the color contrast by manipulating the spectrum to some degree. For example, a neodymium lamp, which absorbs the yellow spectrum, is sold on the Dr. Mitsuru Tanaka LER = 415 lm/WA problem in the Color Rendering IndexThere is no guarantee that saturated colorswill appear pleasant even for large valuesRGB model (Ra=80) dull color3-LED modelPeak wavelength : 457、540、 605 nmLEDRef.CRI a = 80R 9 = -90R400700600500Ref.TestCIELAB466/538/603Fig. 1 A problem in the Color Rendering Index.

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