EagleLight’s LED University: Color Rendering Index CRI Explained
Color Rendering Index (CRI)
In this installment of EagleLight’s LED University we will discuss the color rendering index: CRI explained.
LED CRI Defined
The Color Rendering Index (CRI) is the relative ability of a light source to replicate colors generated by a reference light source of the same color temperature. It is measured as a number between 0 and 100.
LED CRI Explained
This measurement is often used to compare a light sources ability to replicate the sun. In this case the sun is the reference light source. In layman’s terms a CRI of 80 means that the LED light bulb is replicating 80% of the visible color spectrum that the sun would produce at the same color temperature. A CRI of 100%, taken at a color temperature of noon day sunlight will exactly reproduce the colors found on a sunny day at noon. A CRI of 50% taken at noon day sun will partially reproduce the colors when compared to that of a normal noon day.
Examples of Color Temperature and CRI
|Light Source||Color Temperature||Color Rendering Index|
|High Pressure Sodium||2100k||25 CRI|
|Tungsten Halogen||3200k||95 CRI|
|Cool White||4200k||62 CRI|
|Clear Metal Halide||5500k||60 CRI|
|Natural Sunlight||5000-6000k||100 CRI|
|Daylight Bulb||6400k||80 CRI|
Watch the fine print
Some marketers use differing color temperatures as a reference to attain 100% CRI, when the actual CRI would be much less than 100% if noon day sun light was used as a reference.
For the Scientist
If this has not confused you, try this Wikipedia definition:
CRI is a quantitatively measurable index, not a subjective one. A reference source, such as black body radiation, is defined as having a CRI of 100 (this is why incandescent lamps have that rating, as they are, in effect, almost blackbody radiators), and the test source with the same color temperature is compared against this. Both sources are used to illuminate eight standard samples. The perceived colors under the reference and test illumination (measured in the CIE 1931 color space) are compared using a standard formula, and averaged over the number of samples taken (usually eight) to get the final CRI. Because eight samples are usually used, manufacturers use the prefix “octo-” on their high-CRI lamps.”