Air Cooling for LED Lighting

Abstract

A Light Emitting Diode (LED) is a semiconductor that converts electrical energy into light and heat. Typically, energy conversion efficiencies, i.e., the percentage of input energy converted to light, are in the 20–40 % range, resulting in a significant amount of heat being generated in the pn junction of the LED. In most applications, this heat has to be conducted away from the junction and then convected and/or radiated to the ambient air. The convective part of the heat transfer usually requires extended surfaces or heat sinks and in many cases, a method of creating airflow over the heat sink to transport the heat away into the ambient, and is generally referred to as air-side heat transfer. This chapter will discuss the various methods that can be employed for air-side heat transfer. The chapter is divided into five major sections. Section 2 deals with the system-level thermal management of LEDs and discusses the importance of cooling LEDs as well as the various thermal paths and resistances involved in a typical LED system. Section 3 describes the fundamentals of both natural and forced convection heat transfer, including some basic relations and equations used in convective heat transfer. Section 4 describes the different technologies that exist today for air-side heat transfer. Section 5 compares the different technologies with respect to the system-level metrics such as acoustics, power consumption, reliability, etc., required for designing a cooling solution. Finally, Sect. 6 summarizes the chapter.