Investigation into the stability condition of correlated color temperature of white illumination sources based on trichromatic light-emitting diodes

We present a simple method to obtain a stable correlated color temperature (CCT) for the variation in light output power (LOP) of a light-emitting diode (LED) comprising a trichromatic LED-based white light source. A mathematical model was developed to determine the condition for the stable CCT operation using colorimetric analyses, and the stable CCT condition can be obtained by taking the derivative of the CCT with respect to the power ratio between the LEDs. Specifically, the stable CCT point that is invariant to the change in the LOP of a green LED can be uniquely determined at a certain value of the power ratio between red and blue LEDs. It was found that the chromaticity coordinate of the mixed white light moves along the isoCCT line of the Planckian locus as the LOP of a green LED varied under the stable CCT condition. The existence of the stable CCT point was also verified experimentally. The proposed method is expected to be advantageously employed in optimizing trichromatic LED-based white illumination sources for improved color stability.