LED high bay:High Quality LEDs

In general, high quality LEDs are robust devices that can operate in high ambient temperatures. The CREE XM-L LEDs, for example, can operate at a junction temperature up to 150°C. At ambient temperatures of 60°C, the relative light output of LED luminaires is dropped by only 10% compared to relative light output at 25°C. In the LED industry, thermal resistance is used to designate the heat transfer ability of the device as a whole. The LEDs themselves have been engineered with a low thermal resistance path from the junction to the package from where the heat is spread. The thermal resistance of LED packages along with the maximum operating temperature decides the maximum power that can be dissipated in the package. The maximum forward current is determined by the thermal resistance between the LED junction and ambient. For LEDs with high thermal resistance, significant amounts of heat accumulates in the LED, ending up with high LED junction temperatures. When this happens, the effects of increasing LED junction temperature can counterbalance the effects of increased forward current, making the LED to maintain or even lower its light output level even with increases in the forward current as a result of LED's rising junction temperature. It is very important for the luminaire to be designed in a manner that minimizes the thermal resistance from the solder point to ambient with the intention to optimize luminaire life and optical characteristics. The OSLON Square LED family presented by OSRAM Opto Semiconductors features a low thermal resistance of only 3.8 K/W that withstands high ambient temperatures particularly well and can reach a lifetime of considerably more than 50,000 hours even at high temperatures of up to 135°C in the LED. The Lumileds LUXEON K2 white LEDs deliver 70% lumen maintenance at 50,000 hours of operation at a forward current of 1000 mA, based on constant current operation with junction temperature maintained at or below 120°C. It can perform at junction temperatures as high as 150°C without compromising output.