Temperature stability of colored LED elements
Temperature stability of the optical power output of colored (blue-red) light emitting diode (LED) elements is considered. It is shown that LEDs based on blue 455 nm semiconductor chips have the best thermal stability, which is expressed in just 4 % of optical power losses with LED board temperature increasing from 25 °C up to 50 °C. The value of optical power losses for red chips emitting at 660 nm and 730 nm were 7 % and 11 %, respectively, while devices based on 455 nm blue chips and red nitride phosphors with 2 % and 8 % phosphor concentration showed losses of 4 % and 8 %, respectively. Wall plug efficiency of the studied samples demonstrated a similar trend with the temperature increasing as the optical power did.