LED high bay luminaires offer many advantages over traditional HID high bays, these advantages include lower energy consumption, higher outputs at higher drive currents, longer lifetime, improved robustness, smaller size, faster switching, and excellent durability and reliability. A significant problem associated with the use of solid-state lighting, however, concerns complications that result from overheating of the LEDs.
LED: The Heat & Light Source
Solid state lighting devices as represented by light emitting diodes are based on the semiconductor diode. When the diode is forward biased (activated or switched on), electrons recombine with holes and energy is released in the form of light. As a byproduct of converting electricity into light, these optoelectronic devices generate heat which may raise the operating temperature, ultimately causing efficiency degradation and premature failure, if the heat is allowed to accumulate. The performance of a LED typically depends on the ability to manage its junction temperature to achieve an optimum steady-state operating temperature. An elevated junction temperature often correlates to lower light output, lower luminaire efficiency, dominant wavelength, and even reduced life expectancy. The junction temperature of the LED significantly impacts both its L70 life and its overall efficiency. In general every 10°C increase (above 25°C) in junction temperature can reduce the life time of the LED by 10 kHrs (1000 hours) for a gallium nitride (GaN) LED. Increasing the junction temperature from 40°C to a 70°C will cut down the efficacy of the LEDs by more than 10%. Thus, appropriate thermal management solutions must be developed to ensure performance is maintained and the operating temperature of the LED fixture is controlled for a given change in the junction temperature and the ambient temperature.
