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Color-rendering-index-(CRI)

CRI > 90,80 – WHAT IS THE COLOR RENDERING INDEX (CRI) IN LIGHTING?

Have you ever searched for what is color rendering index in lighting?

In lighting, the definition for Color Rendering Index (CRI) measures the ability of a light source to accurately reproduce the colors of the object it illuminates, or technically a CRI is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with an ideal or natural light source. This is a seemingly simple definition, but there is a lot going on, so we’ll help break it down into three parts

Part 1 : Color Rendering Index (CRI) is a score with a maximum of 100

What does it mean to measure the ability of something? Like test scores, CRI is measured on a scale where a higher number represents a higher ability, with 100 being the highest. CRI is a convenient metric because it is represented as a single, quantified number.

CRI values that are (color rendering index) 90 and above are considered excellent, while scores below 80 are generally considered poor. (More on this below).

Part 2 : Color Rendering Index (CRI) is used to measure artificial, white light sources

Light sources can be grouped into either artificial or natural light sources. In most situations, we are concerned about the color quality of artificial forms of lighting, such as LED and fluorescent lamps.

This is compared to a daylight or sunlight – a natural light source.

Part 3 : Color Rendering Index (CRI) measures and compares the reflected color of an object under artificial lighting

First, a quick refresher on how color works. Natural light such as sunlight is a combination of all the colors of the visible spectrum. The color of sunlight itself is white, but the color of an object under the sun is determined by the colors that it reflects.In

A red apple, for example, appears red because it absorbs all colors of the spectrum except red, which it reflects. When we use an artificial light source such as an LED lamp, we are attempting to “reproduce” the colors of natural daylight such that objects appear the same as they do under natural daylight.

Sometimes, the reproduced color will appear quite similar, other times quite different. It is this similarity that CRI measures.

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1. What do the Color Rendering Index (CRI) values mean?

The table below shows the general ratings for the Color Rendering Index Ra indices and what they represent. Reasonably enough, the higher the Ra of a light source, the more accurately it renders the objects’ colors. With a Ra below 80, noticeable color distortions begin to appear, while with a Ra less than 60, objects may start to look unappealing or unnatural.

Here is the color rendering index chart for reference;

color-rendering-index-table-ra-rating-what-it-means-northerncult blog

2. Why is it important to know CRI values while designing light?

When a new project comes along, the lighting designers, need to select the appropriate luminaires and light sources for the space we want to transform with the light. As said before, the higher CRI, the better the color rendering. 

However, when it comes to implementing this in the design, how should the designer choose a suitable CRI? Of course, this depends on the type of space, its requirements, and practical purposes. And, we should certainly not forget that subjectivity can play a role in our design in terms of aesthetics and the client’s requirements.

color-rendering-index-table-ra-scale-application-examples-northerncult-blog

CONCLUSION

Good color rendering doesn’t only have to do with objects and the architecture of the space, but also with people’s skin tone. Whether the light fittings make human skin appear healthy, flattering, or sick, affects how people feel and can create an emotional connection to the whole space. The designer should be mindful when choosing light sources especially in areas where a person’s appearance may be closely examined, such as hospitals, fitting rooms in retailing or beauty, and cosmetics stores.

Color rendering is an important factor to take into account when lighting museums and galleries. The Color Rendering Index (Ra) gives a general indication of the rendering ability of a light source.

A Color rendering index of 90 is ‘best or true’, whilst those over 80 are considered good. The aim of any curator is to have an object appear as ‘natural’ as possible when lit. However, LEDs traditionally create white light by combining blue light with a yellow phosphor, making them better at lighting blues than reds in the color spectrum. The end result can be washed out reds and skin-tones. To avoid this, LEDs with a CRI of >90 are best for galleries and museums, to ensure punchily, vibrant reds.

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