How do the color rendering characteristics of LEDs compare to other light sources?
Typical phosphor-based white LEDs have color rendering index (CRI) values comparable to discharge lamps (fluorescent and high intensity discharge) used in many lighting applications. Common belief is that high CRI means good color rendering properties. CRI is actually an index of how similar a light source makes colors appear in comparison to a reference source such as incandescent (which is why an incandescent lamp has a CRI near 100). For mixed-color LED systems, CRI is very sensitive to the wavelengths of the component colors; however, this sensitivity is not necessarily representative of one’s preference for color appearance in an actual application. Recent studies have shown that mixed-color white LED systems with CRI in the 20s can result in higher color preference than systems with CRI in the 90s (Narendran and Deng 2002b). Knowing the limitations of CRI, international standard-setting bodies are working to explore newer metrics for better characterizing the color rendering properties of all light sources, including LEDs.