How the Light Illuminates the Environment
The CCT designation gives a good idea of the light’s general appearance, but does not always tell you how it will illuminate different colors. Two lights with the same CCT may be dramatically different in how they show color due to their inherent radiant characteristics.
To easily describe and compare these characteristics simply the Color Rendering Index (CRI) was developed. The CRI is a numeric representation of a light bulb's ability to show colors "realistically," compared to a reference light source of the same color. The CRI scale ranges from 0 to 100—the higher the number, the more natural the colors will look to you. For good color quality, look for lights with CRIs of 70 or above.
Since the CRI rating for any given lamp is an average of eight test results, it can give no particular insight into the effect of the appearance of any one color. In the example below, the two light sources illuminating the object have a CRI of 70, however the light source on the right renders blue more naturally than the one on the left.
|-Renders Blue less naturally||-Renders Blue more naturally|
The Department of Energy acknowledges the limitations of the CRI, especially when applied to bright white LED’s. They have the following recommendations:
"A long-term research and development process is underway to develop a revised color quality metric that would be applicable to all white light sources. In the meantime, CRI can be considered as one data point in evaluating white LED products and systems. It should not be used to make product selections in the absence of in-person and on-site evaluations." For more information on this topic, see the DOE site here.