Thecolor rendering index(CRI) of a light source is a quantitative measure of its ability to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source. It is significant because it has been the most difficult metric for incandescent replacement light bulbs to match (while maintaining high efficiency) and therefore the most frequently ignored. For that reason, LED light bulbs with a high CRI can be worthy replacements for incandescent light bulbs. Most LED lights do not have a CRI above 90.

However, CRI is a poor indicator of the perception of light produced by LEDs, and scores as low as 25 can produce vivid-appearing white light, while high-scoring sources can still be very poor at rendering reds, including skin tones.

In 2008, the US Department of Energy created the L Prize to find an incandescent light bulb replacement that met efficiency metrics and had a CRI above 90.