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How different light sources render color is important in building design when selecting the right ones

Have you found out sometimes the color of the dress you picked from the store, appears too bright when you actually wear it later? You will instantly realize the lighting had something to do with it, but what’s truly happened there is a well-known subject area among lighting specialists.

Apart from ‘Brightness’, any light source has specific attributes which determine the rendition of colors of an object when its light fell on. The white light that the sun produces is saturated with different colors called the visible light spectrum. So when you see orange in sunlight, it appears orange because it reflects sunlight’s orange components much more than any other color in the spectrum. What happens if the sun stops emitting orange components? You will definitely see oranges in a different color. And do all artificial lights emit the full visible spectrum? The answer is no, and that’s what decided this text should exist.

What is CRI?

CRI or the ‘Color Rendering Index is a measurement of color fidelity. It is measured on a 0 to 100 scale and is the most used measurement in specifying the color illumination quality of a light source. ‘Correlated Color Temperature or CCT is another measurement of a light source sometimes confused with the CRI.

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Generally, the Sun and incandescent lights are considered perfect light sources with a 100 CRI value. ‘International Commission on Illumination’ has standardized a set of eight pastel colors to carry out CRI tests for any light source. These colors will be illuminated under a particular light source and then compared its results against the outcomes of the same for a perfect light source. Carried under comparable brightness values and CCT conditions, the CRI value of that light source is determined by averaging the color differences resulted from the two sources. A small average portrays a high CRI value. Thus, the higher the CRI value of a light source is, the more realistic the colors it will illuminate. A low CRI value is an indication that the light source will illuminate some colors unnaturally or unrealistically. Over time extended color pallets with 15 colors have been introduced in testing to get more accurate results on saturated colors, skin tones, and foliage. These come in handy for Architects and Designers when selecting the proper light sources for various projects. Then again the CRI value doesn’t indicate a light source’s ability to illuminate varying properties of a specific color like Saturation or Lightness. With the Growing usage of LED light sources, many types of research have been performed to measure the color fidelity properties of different LED applications. It is found on many occasions that with LED, unlike any other type, light sources can perform different color saturations even of similar CRI and CCT values.

What is TM 30?

A regular criticism of the traditional CRI system has led lighting specialists to come up with ‘TM 30’ which is a more comprehensive system. Advantageously, with TM 30 we get much additional information other than the color fidelity metric of a light source.

  • Rf - Fidelity Index
  • Rg – Gamut Index (Saturation)
  • Color vector graphic

Rf or the Fidelity Index is a measurement scaling from 0 to 100. Adapting a parallel method as CRI, 99 color samples are being tested with reference to a perfect light source. Correctly, compared to the CRI, these 99 samples contain more real-life color instances, distinguishing its representativeness both quantitatively and qualitatively.

‘Chroma’ was the missing component in the CRI. Saturation or the intensity of an illuminated color is identified as Chroma and it is measured in the TM 30 system as Rg or the Gamut Index. Here it will not indicate the saturation of a specific color but a general indication (preferable when comparing equivalent fidelity light sources). 100 is the neutral Rg value where a value of 80 will illuminate colors paler and a value of 120 will lighten them more saturated.

‘Color vector graphic’ enables Designers and Architects to contemplate on vividness or the dullness of any specific color complimenting both Rf and Rg values at the same time.

Let’s take the above sample and extract some of its information.

The black Ring - Reference Light (Sun in many cases)

Red ring - Test Light

16 Arrow projections - Shifts of Hue Bins (compared with the reference light source)

Note: Hue Bins are categorized colors in the spectrum for easy indication

Wherever the red ring is inside of the black ring indicates paler colors compared to the reference. Oppositely saturated colors are indicated in the instances where the red ring is outside of the black ring. It means a Hue shift when the red ring’s whole shape is shifted. Overlapping of both rings signifies no difference in color illumination of both light sources.

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Applying Color Rendering to Building Design

Urban Design, Architecture, Landscape Architecture, Interior Design, and whatever you name, Building design is a broad subject area that artificial lighting plays a crucial part.

"Light is the first element of design; without it there is no color, form, or texture."

Thomas E. Farin - lighting specialist

Architects and designers are always searching for two goals whenever they’re obsessed with their designs. Those are namely, ‘Functional value’ and the ‘Aesthetical value.’ In a modern-day built environment, one cannot simply achieve both goals without giving attention to artificial lighting.

By and large, a good color rendering quality is required in fashion design studios, ateliers and art galleries, manufacturing factories, and some high-end retail. Even though it is widely accepted that CRI values of 90 or over are satisfactory in many cases, the above list will prefer CRI values closer to 100. In such applications, Architects and designers are restricted in experimenting with the color illuminating fidelity of a light source (CRI or the Rg).

However depending on the aesthetical and the emotional nature of the function, designers can experiment with the color temperatures. As discussed earlier, CCT or the color temperature is often confused with CRI.

Derived from the electromagnetic spectrum, CCT is measured in Kelvin. The scale of color temperature is determined by the light emission of heated metal. As we start heating a piece of metal until its incandescence, it will emit colors starting from red, yellow, white, and lastly blue. Thus the higher the Kelvin value is the cooler the light source is.

Throughout the world, human perception finds the red color, more intimate and coherent than any other color. Scholars doubt it dates back to the primitive man and from cultural understanding as well. However, experimenting with High Rg values will be interesting for architects when designing musical and theatrical environments where you don’t need special attention to distinguished color. It is guaranteed the more reddish spatial vibe is the more emotional it gets, could be applied anywhere else.

Hopefully, you are now well educated about the Principles of color rendering quality of different light sources. So when you visit the fashion store again, don’t forget to remember the CRI and TM 30.