Philips Lighting Research North America, Cambridge, MA
Color rendering is often considered within four conceptual frameworks; color fidelity (the rendition of objects such that they appear as they would under a familiar reference illuminant), color preference (the rendition of objects such that they appear pleasant, vivid, or flattering), color memory (the recollection of colors based on memory), and color discrimination (the ability to distinguish colors of slightly different hue when viewed simultaneously). Color discrimination has been studied less frequently than color fidelity or color preference, though it is no less important. This presentation will summarize the previous literature on color discrimination and discuss recent work in this area. Of particular interest will be a recently published study by the current author, which dispels the conventional wisdom that gamut area is a predictive color discrimination metric. This presentation will detail a new measure of color discrimination, which shows strong predictive ability of experimental results.
Yuki Kawashima and Yoshi Ohno
National Institute of Standards and Technology, USA
Hunt Effect implies that perceived chroma decreases at low light levels compared to that at higher light levels. However, detailed experimental data have not been available. If this effect is active at the light level of general lighting, light sources that increase chroma slightly (than the reference illuminant) would produce higher color fidelity than those exactly matched to the reference illuminant. To prove whether such Hunt Effect is effective at normal indoor lighting, vision experiments have been conducted at NIST using the Spectrally Tunable Lighting Facility. 24 subjects viewed real fruits and vegetables and their skin tones under 9 different chroma levels in red-green direction, frm -16 to +16 ?C*ab (measured for a red sample from the reference illuminant), at illuminance levels of 100 lx and 1000 lx, and evaluated naturalness of these targets. Results showed significant differences between 100 lx and 1000 lx: subjects perceived targets as most natural at less chroma level (by ~ 0 to 8 ?C*ab depending on target) at 1000 lx than at 100 lx.
Lorne A. Whitehead
University of British Columbia, Vancouver, Canada
We are entering an exciting period for improving the human value of electric light sources, now that both the IES and the CIE have agreed upon a common set of 99 standard color evaluation samples. These provide a common framework for assessing the impacts of light sources on the color appearance of surfaces. There is a complicated design tradeoff involving three other characteristics - chromaticity, efficacy, and cost. Some discussions about this have omitted the important fact that it is an object’s spectral radiance factor (and not its color) that predominantly determines the color shift caused by the light source. This effect is lost in summaries about color rendering that describe the average color shifts of objects of specified hues. Currently, there are concerns about how best to address this when summarizing the detailed CIE/IES color shift data, to assist lighting designers and researchers. Suggestions for summarizing this will be presented.
Yoshi Ohno1, Semin Oh2, and Youngshin Kwak2
1 National Institute of Standards and Technology (NIST), Gaithersburg, MD, USA
2 Ulsan National Institute of Science and Technology, Korea
Color Rendering Index (CRI) Ra value, for some types of light sources, does not correlate well with visual evaluation, especially when object chroma is increased by the light source. Increased chroma is known to be a major factor for color quality preference in lighting, and gamut area measures are often used to evaluate the preference aspects. However, gamut area accounts for chroma differences equally for all directions of hue. It is demonstrated that preference differs very much depending on the shape of the gamut even though the gamut index value are the same. Vision experiments were conducted at NIST in 2016 to obtain relationship between preference and chroma increase in different hue directions, using 11 different gamut shapes, using NIST Spectrally Tunable Lighting Facility with 19 subjects. To verify these results, this experiment was repeated in the summer of 2017 with 22 subjects with slightly improved gamut shape settings, for 3500 K and 5000 K conditions. The results were similar to those in 2016, showing the dominant effect of red color, and much less effects of chroma changes of other colors. An idea of a color quality preference model based on these results is discussed.
Joanne Zwinkels1, Éric Côté1, and John Morgan2
1National Research Council of Canada, Ottawa, Canada;
2University of Waterloo, Waterloo, Canada
Specular gloss is an important appearance property of a wide variety of manufactured goods. Depending upon the application, e.g. paints, paper, ceramics, etc. different instrument designs and measurement geometries are specified in standard test methods. For a given specular angle, these instrument designs can be broadly classified as converging beam (TAPPI method) and collimated beam (DIN method). In recent comparisons of specular gloss measurements using different glossmeters, very large standard deviations have been reported, well exceeding the manufacturers claims. In this paper, we investigate the effect of instrument beam geometry on gloss measurements. These results indicate that this difference in beam geometry can give the magnitude of gloss differences reported in these comparisons and highlights the importance of educating the user community of best measurement practices and obtaining appropriate traceability for their glossmeters.
Wei-Chung Cheng and Aldo Badano
Center for Devices and Radiological Health, U.S. Food and Drug Administration,
Silver Spring, MD 20993, USA
Colorimetrical characteristics are critical factors in assessing performance of medical imaging devices used in various modalities including digital pathology, endoscopy, dermatology, and ophthalmology. Medical imaging devices usually comprise image acquisition and image display subsystems, and color performance depends on not only the individual subsystems but also the interactions between them. In this presentation, we describe three bench-test methods developed for assessing digital pathology whole-slide imaging (WSI) systems. A multispectral imaging method was used to measure the color truth of biological tissue slides such that the color reproducibility of WSI scanners can be compared. Quantitative metrics were used to evaluate colorimetrical characteristics of color medical displays. Finally an electronic apparatus was used to verify the color management behavior of the complete system.
Jennifer A. Veitch
National Research Council Canada (NRC), Ottawa, ON, Canada
Director, CIE Division 3
Changes in lighting and daylighting equipment and their related control technologies have touched all parts of the industry around the globe, and are well on the way to touching the lives of all users of electric lighting. In parallel, our understanding of how radiation between 380 – 780 nm affects human physiology and behavior is expanding. The excitement began 15 years ago with the confirmation of the existence of intrinsically photoreceptive retinal ganglion cells (ipRGCs), which touched off a race to identify new ways to use light to influence well-being and health. As the capabilities of technology grow, so too does our knowledge expand to identify possible new applications. These forces combine to create unprecedented opportunities, but also bring challenges. Circadian regulation is one process linked to the ipRGCs, and study of that relationship has shown that the intensity, duration, spectrum, timing, and pattern of light exposure all influence daily physiological and behavioral patterns. Perhaps this means that we could use the new dynamic lighting systems to deliver variable light exposures to support health and well-being. How might we combine this with using lighting to create context-appropriate conditions consistent with achieving good lighting quality? Are there any risks associated with the new lighting technologies that we should take into account? This presentation will describe the current state of knowledge in this broad field, and will introduce a roadmap to improved understanding that could support new lighting recommendations.
David H. Sliney
USA Center for Health Promotion and Preventative Medicine, Aberdeen Proving Ground, MD (ret.), and
Johns Hopkins University Bloomberg School of Public Health, Baltimore.
Although a great deal of attention has been paid to the spectral characteristics of light exposures in circadian/health applications of lighting, there has been insufficient recognition of the importance of spatial distribution of light reaching the retina. Measuring only horizontal or vertical illuminance or a spectrally weighted vertical irradiance without significantly limiting the field-of-view ignores the potentially widely varying impact of the spatial distribution of environmental light upon the melanopic or “circadian” stimulus. The use of horizontal irradiance or illuminance that equally treats the upper and lower quadraspheres also will typically result in serious errors – including a completely opposite picture of the true retinal exposure. The time-weighting of retinal exposures is also of importance, but the available evidence for a clear metric is still lacking.
Philips Lighting, Burlington, MA
NEMA has published a standard (NEMA 77) for temporal light artifacts (TLA), which presents measurement methods and gives guidelines for quantification of TLA. Two measures are used: IEC’s short-term flicker indicator (Pst) for flicker (< 70-80 Hz) and the stroboscopic visibility measure (SVM) for stroboscopic effect (> 70-80 Hz). Both measures are based on work with human observers to include human sensitivity in the measures. The presentation will describe the NEMA work and compare the measures with other measures, including IEEE 1789, and ASSIST, as well as with the actual performance of common light sources.
Ilko K. Ilev, Robert James, and Robert Landry
Optical Therapeutics and Medical Nanophotonics Laboratory
Office of Science and Engineering Laboratories, Center for Devices and Radiological Health
U.S. Food and Drug Administration, Silver Spring, Maryland 20993
Light Emitting Diodes (LEDs) have been developed recently as replacement lamps for both tungsten-based lamps and Compact Fluorescent Lamps (CFLs) for general illumination purposes. LEDs have specific advantages in terms of a longer life and use less energy when compared to both CFL and tungsten based lamps. Unfortunately, if not designed properly, these light sources could potentially present an optical radiation hazard to the retina, due in part to the small size of the light-emitting area, the relatively high blue spectral content, and the intensity of the light output. The present study is focused on quantitative standard evaluation of the potential for ocular damage from optical radiation emitted by LED sources used for general illumination. We have evaluated all LED test samples in compliance with the standard procedures specified in ANSI/IESNA Standard ANSI RP-27.3. The spectral irradiance was measured using a double-grating spectroradiometer system in the wavelength range of 250-800 nm. The main results of the study indicate that the evaluated LEDs fall in the category of Exempt Group (with no physiological hazard) except for an additionally tested LED lantern classified in Risk Group 2 (moderate risk), and a 100 W incandescent lamp classified in Risk Group 1 (low risk). The presentation will also report and discuss on measuring approaches employed for evaluating broadband spectral and optical radiation dosimetric characteristics of LED and fluorescence lamp sources emitting in the UVA and UVB spectral ranges used in 3D cell bioprinting.
Lorne A. Whitehead
University of British Columbia, Vancouver, Canada
For a long time, near-infrared radiation (NIR) has seemed, from the perspective of illuminating engineering, to be both useless and harmless. For this reason, it has been largely ignored, and considered to be merely a wasteful by-product produced by some light sources. Two recent developments suggest it may be time to reconsider this. First, medical researchers have determined that NIR can be effective in treating certain diseases, primarily through absorption by the important metabolic enzyme, cytochrome c oxidase. This raises the possibility that NIR, which is abundant in natural light, may be actually be healthful. The second development is that the average exposure of people to NIR is dropping through ongoing replacement of NIR-rich incandescent lamps with LED lamps that have been carefully engineered to emit very little NIR light. I will suggest that there is a need for careful studies to check on whether NIR can and should beneficially contribute to health.