Thermocouple is often used to measure surface temperature of light emitting diode (LED). However, it was found that the method was not accurate in this work. An experiment was conducted to prove this in the first part. In the experiment, the air temperature above a lit LED chip was measured by a thermocouple, and it was found the measurement temperatures were higher than the LED junction temperatures. When the drive current was 1000 mA, the deviation reached as much as 148.61%, which proved that the temperature measured by the thermocouple was not accurate. The reason for the inaccuracy was supposed to be the absorption of the optical energy by the thermocouple. Theoretical derivation was conducted and it was found that the measurement temperature was related with the local luminance around the thermocouple and the optical absorption coefficient of the thermocouple. Comparison experiments were conducted and qualitatively validated the supposition. (C) 2013 Elsevier Ltd. All rights reserved.