Phosphor Concentration Effects on the Thermal and Optical Performance of Cool and Warm White Single Chip Light Emitting Diodes

Hsien Shiung Hwang,  Anithambigai Permal,  Mutharasu Devarajan
Nano Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia


Phosphor converted light emitting diodes (LEDs) are emerging as the most promising solid state lighting source for the past few decades and with no doubt in few years to come, this technology would conveniently replace the current lighting industries. This paper elucidates the significance of thermal and optical performance difference between cool and warm white LEDs. The analyses were carried out in terms of effects of phosphor concentration on the rise in junction temperature, thermal resistance as well as the optical properties of the samples. It was observed that the cool white samples achieved 6.68% less junction temperature compared to warm white LED recorded at room temperature of 25.1˚C and the average efficiency of the cool white LED was found to be higher in magnitude compared to warm white LEDs. The effects of phosphor concentration on degradation of LED performances were discussed in terms of photon scattering, light trapping and thermal loading phenomena.