The area-source light emitted by OLED devices differs from point-source light from other devices such as incandescent lamps or LEDs, or line-source light emitted by fluorescent lamps, for example.
The white-emission OLED device used for displays is very similar to the OLED lighting device (Figs. 7.1 and 7.2), so the display techniques are mostly applicable in lighting applications. However, the specification for a lighting application should differ from that for a display. In particular, the light source must provide adequate color reproduction of the irradiated object. This metric is called the color rendering index (CRI).
The color rendering index (CRI) is widely used to demontrate the color reproduction of reflected light in lighting applications.
For the color rendering index calculation, the CIE1964 uniform color space (U*,V*,W*) coordinate system is used (this color coordinate applies only for the color rendering index calculation):