Tutorial: Color Rendering and Its Applications in Lighting

Abstract

This tutorial explains how the human perception of color rendering arises, in terms of the underlying phenomena of light and vision, and using those concepts it presents a clear explanation of the CIE Color Rendering Index. The strengths and weaknesses of the CIE Color Rendering Index are reviewed and some common misunderstandings about color rendering are addressed. It is suitable for self-study, with learning outcomes stated at the beginning and a conceptual summary provided at the end. KEYWORDS Learning OutcomesIt is our intent that, after studying this article, the reader will:1. be able to explain the basic concept of color rendering 1 -what is being measured, why is it important, and how it influences the design and selection of electric light sources; 2. feel familiar with basic concepts of optical science and color vision that are required to understand color rendering: spectral power distribution, correlated color temperature, chromaticity, spectral reflectance function, chromatic adaptation, color appearance; 3. be able to describe the basic concepts underlying color rendering: test illuminant, reference illuminant, test color samples, color shift, color difference; 4. understand that the current CIE method for calculating the General ColorRendering Index (R a ) 2 is useful but not perfectly accurate: it is being updated to further improve its accuracy; 5. understand that R a is a limited measure; by definition it overlooks important factors that may also warrant consideration by other methods: (a) objects will sometimes appear a slightly different color when illuminated with lamps of different color temperature, even if both lamps have perfect color rendering; (b) Special Color Rendering Index (R i ) values can provide information about how a lamp causes color shifts for specific test color samples; and (c) beyond the concept of color rendering, there are other ways to summarize the color shifts that occur with lamps that have imperfect color rendering, which may be helpful for some lighting applications-in other words, color rendering does not tell the full story.7

Interpreting Art with Light: Museum Lighting between Objectivity and Hyperrealism

“…With this method, color consistency remains constant across several luminaires that target different zones within the artwork. However, the composition of the light spectrum is modified on each individual spotlight using the various color channels-the result is that certain material colors in individual zones of the image or within an exhibition have a different effect and that color rendering is therefore modified (Csuti et al 2015;Houser et al 2016;Schanda et al 2016). This process enables single colors-for example, a blue sky-to be emphasized in terms of color impression while avoiding the shifting of colors toward blue elsewhere in the image or on other artworks in the exhibition room.…”

56.3: Invited Paper: New Color Rendering Standards and Implications for Displays that Provide Illumination: The Promise and Peril of Solid State Lighting

“…Therefore, we should try to minimize surface color distortion. Light sources that fulfill this requirement are said to have high color rendering [6].…”

Solid‐State Lighting for Illumination and Displays: Opportunities and Challenges for Color Excellence

“…Light sources that fulfill this requirement are said to have high color rendering. 13 This idea is quantified by the CIE Color Rendering Index. 14 So, how do LEDs impact color rendering?…”