Influence of wavelength red-shift on color-rendering index and luminous efficacy of LEDs

The peak wavelength of light-emitting-diodes (LEDs) shifts towards the longer wavelengths when the temperature of the LED chip increases. The color-rendering index (CRI) and luminous efficacy may change with the peak wavelength of the LED, and it is not expected to do so when the LEDs are used in fields which require a high CRI and luminous efficacy. A mathematical model of the LED spectrum was used to analyze the influence of the wavelength shift on the CRI and luminous efficacy of three-and four-chip-packaged LEDs, respectively. The results show that the CRI decreases with the peak wavelengths shifting towards longer wavelength for both three-and four-chip LEDs; especially, the CRI of the four-chip LEDs decreases more for a green-color wavelength shift than for other colors. The luminous efficacy increases with a green-color wavelength shift and decreases with a red-color wavelength shift.