An experimental investigation of the thermal characteristic of the LED chip and the sensitivity of illumination with thermal substrate is discussed in this study. An optimum thermal diffusion area to the heat flux of LED system is also conducted. Results show that a red LED chip has lower electrical resistance, and therefore has lower power consumption than that of green and blue LED chips. Given these three colors of lighting LEDs, the red LED chip is more sensitive to the thermal environment. A red LED's lighting illumination is decreased almost 12% when the substrate temperature difference is increased to 25 °C. Under the same condition, an LED's illumination experiences only a 2 to 2.5% reduction for the green and blue LED chip.Thermal diffusion area results show a close correlation between thermal diffusion ratio and LED substrate temperature. If the upper limit LED substrate temperature is set at 50 °C and the thermal diffusion ratio approximates 72 cm 2