Color rendering describes how a light source makes the color of an object appear to the human eyes and how well subtle variations in color shades are revealed. The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering color when compared to a "reference" light source.
In many cases, this difference is not important. However, for certain applications such as illuminating art or comparing fabric in retail clothing stores, CRI can make all the difference. There is also evidence that high CRI bulbs might be perceived to be brighter which could allow for the installation of lower wattage bulbs to save energy. Numerically, the highest possible CRI value is 100 and would only be given to a source identical to standardized daylight (sunlight).