The thermocouple is often used to measure the LED surface
temperature. In this work, we investigated the accuracy of such a
measurement method. A measurement experiment was designed
and it was found that the temperature of air above the LED chip
measured by the thermocouple was higher than the LED junction
temperature, which is unreasonable. This proved that such a mea-
surement is not accurate. It was supposed that the inaccuracy re-
sulted from the absorption of optical energy. Theoretical
derivation was presented and comparison experiment was con-
ducted to validate this supposition. The results showed that the
measurement error depends on the local luminance around the