The color rendering index, also known as the CRI or Ra value, provides information about the quality of the color rendering of a light source. Let’s talk about CRI and learn how to achieve natural-looking lighting with LED lamps.
Color rendering index definition
The color rendering index indicates how naturally the colors of objects or their surroundings appear with the light of a particular light source. It is a comparative value with which the color impression of a light source can be determined. With the help of the color rendering index, the light quality of different illuminants can be compared. The following terms are also commonly used:
Color Rendering Index (CRI)
Rendering index (R)
General rendering index (Ra)
All designations and their abbreviations refer to the color rendering index. For many lamps, the index is indicated as a CRI value or Ra value on the packaging or lamp.
The color rendering index has a value between 1 and 100 and has no unit. Natural light (sunlight) has a CRI of 100. Incandescent and halogen lamps also have the maximum color rendering index of 100. Fluorescent lamps, on the other hand, only have a CRI of 60 to 90.
We are used to see illuminated objects in their natural colors from the old light sources with filaments. With fluorescent tubes, the colors of the illuminated objects sometimes look slightly distorted. These look as if someone had put a grey veil over the colors, making them less luminous.
The effect becomes more visible when we go into an environment with red lighting with a red clothing, for example. Here, the red clothing no longer stands out from the red ambient light. If we go into the sunlight with the red clothing with Ra 100, the red color is very noticeable again.