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Organic–Inorganic Semiconductor Heterojunctions for Hybrid Light-Emitting Diodes
Published in Ye Zhou, Optoelectronic Organic–Inorganic Semiconductor Heterojunctions, 2021
A true white light source needs to have the ability to reproduce the real color of the illuminated object accurately. The color rendering index (CRI) is a measure of the ability of a light source to render or reproduce the color of an object faithfully in comparison with the light of an ideal or natural source [22,28]. The CRI is dimensionless, and its maximum value is 100, representing an ideal color rendering source. The CRI is an important parameter to describe the quality of a light source. Light sources in homes or offices should have high color rendering capabilities (high CRI), whereas color rendering is less crucial (lower CRI) for street lights or lights for general illumination. The CRI of a Planckian black body radiator is defined to have the highest color rendering capabilities (CRI of 100), because it most closely resembles natural daylight. The closest light source to a black body radiator is the incandescent light bulb, which (as a black body emitter) has the highest possible CRI of 100, as a consequence all other light sources have a lower CRI.
How to Design a Lighting System
Published in Albert Thumann, Harry Franz, Efficient Electrical Systems Design Handbook, 2020
Color Rendering is a parameter that describes how a light source renders a set of colored surfaces with respect to a black body light source at the same color temperature. The color rendering index (CRI) runs from 0 to 100. It depends upon the specific wavelengths of which the light is composed. A black body has a continuous spectrum and contains all of the colors in the visible spectrum. Fluorescent lamps and high intensity discharge lamps (HID) have a spectrum rich in certain colors and devoid in others. For example, a light source that is rich in blues and low in reds could appear white, but when it is reflected from a substance, it would make red materials appear faded. The same material would appear different when viewed with an incandescent lamp, which has a spectrum that is rich in red.
Color & Light
Published in Michael Stiller, Quality Lighting for High Performance Buildings, 2020
CRI, or color rendering index, which should not be confused with correlated color temperature, is a metric used to gauge the ability of a specific light source to accurately render the color of an object to the viewer. Many of us have had the experience of buying something, such as an article of clothing, only to find it looks quite different once we get it home or when we look at it under daylight. Or perhaps the lighting in a particular environment makes our skin take on an unattractive hue. This is the kind thing that can happen with electric lighting of a low CRI. To establish the CRI of a particular lamp, or source, a series of eight color samples are viewed under the light generated by that source, and then under an ideal light source of the same color temperature. The results are then compared, and a rating is assigned to the source depending on how well, on average, it renders the eight color samples. The CRI of a lamp, or source, is rated on a scale of 1 to 100. Both daylight and incandescent (or halogen) are considered ideal sources, with a CRI score of 100.
Photoreceptor Enhanced Light Therapy (PELT): A Framework for Implementing BiologicallyDirected Integrative Lighting
Published in LEUKOS, 2023
Beatrix Feigl, Drew D. Carter, Andrew J. Zele
The perception of whiteness is subject to individual variations in optical and neural factors between and within observers, and over time (Bosten et al. 2015; Webster 2020). Because the relative outputs of the primary lights vary between the PrD conditions (Fig. 2), any manifest differences in chromatic adaptation between conditions will lead to color after-effects. A patient can however only view one PrD lighting condition at a time. With a maximum CRI of 92 for the evaluated primary combinations, the application of PELT in luminaires in the built environment can further increase color rendering by incorporating additional spectral primaries (e.g., broadband white LEDs). Such component changes must be considered in context of the purpose for they can lead to a reduction in maximum achievable PrD contrast. Similarly, it is yet to be determined how tolerant human vision is to integrative lighting, as advances in circadian spectral optimization may change our understanding of color rendering.
Tutorial: Background and Guidance for Using the ANSI/IES TM-30 Method for Evaluating Light Source Color Rendition
Published in LEUKOS, 2022
Objects or surfaces do not have an inherent color, but rather reflect different proportions of energy over the visible spectrum. When the spectrum emitted by a light source changes, the light reflecting off a surface (the visual stimulus reaching the eye) also changes, which alters how the stimulus is interpreted by the brain. Figures 2 and 3 provide two examples of how color rendition can influence appearance using digitally manipulated images that simulate real color rendition conditions. Officially, the IES and CIE define color rendering as the “effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant.” CIE also defines color rendition as the “effect of an illuminant spectral power distribution on the color appearance of objects” (CIE 2017), which provides a less restrictive definition, even though rendering and rendition are typically considered synonyms.
Change of Gamut Size for Producing Preferred Color Appearance from 20 to 15000 lux
Published in LEUKOS, 2021
In contrast, little effort has been made to investigate how light level affects light source color rendition, though light source color rendition has attracted great interest from the lighting community in recent years. The CIE's General Color Rendering Index Ra (CRI Ra), the most widely used color rendition metric, only characterizes the ability of a light source to render the color appearance of eight test color samples in comparison to a reference illuminant (known as the color fidelity of a light source). It has been found that sources with a high CRI Ra value may not always be preferred and sources that can enhance the saturation of colors, especially the saturation of warm colors, were found preferred (Davis and Ohno 2010; Esposito and Houser 2018; Royer et al. 2018, 2017; Smet and Hanselaer 2016; Wei and Houser 2017; Wei et al. 2014a, 2015, 2017). Therefore, a color gamut measure characterizing the average change in object color chroma and a color vector graphic (or local chroma shift values) characterizing object color chroma change in different hues are recommended to be used with a fidelity measure for better characterizing light source color rendition (e.g., IES TM-30-15; David et al. 2015; IES 2015).