Analysis of the cooling method of LED lamps

There are three channels for LED lamps to dissipate heat: conduction, convection and radiation, and among which the heat conduction method plays the most important role. In order to achieve good thermal conductivity performance, thermal conductive materials should be used reasonably, and convective heat dissipation and radiation should be maximized.

1) Heat conduction.

The matter itself, or when the matter comes into contact with the other matter, the transfer of energy is called heat conduction, which is the most common way of heat transfer

The heat source is critical to heat conduction. The heat source of LED lighting fixtures comes from two parts: the light source and the power supply. For the heat of the light source part, it is usually need to pay attention to the effective contact area between the PCB of light source PCB and the bonding surface of the heat sink. The larger the effective contact area, the better the heat dissipation. In addition, should pay attention on the heat conduction interface between different material, make it as smooth as possible, the bonding between the heat conductors should be close enough, and the contact surface gap of the fitting parts should be as small and as little as possible.

In the heat conduction design of LED lamps, a good heat conduction path should be to reduce the thermal resistance between PCB, heat conduction medium and radiator, to increase the effective contact surface between the three, and choose heat conduction medium with higher thermal conductivity.

2) Convection

Convection refers to the heat transfer method in which fluid (gas or liquid) contacts a solid surface causing the fluid to conduct the heat away from the solid surface. There are two different cases of thermal convection, namely natural convection and forced convection. Natural convection refers to fluid movement, which is caused by temperature differences. Fluids with higher temperatures have lower density, so they are light in weight and move upwards relatively. Forced convection means that the fluid is driven by external forces (such as air flow driven by a fan). Wherever the driving force goes, the fluid moves to where, so this kind of thermal convection is more efficient and directional.

Natural convection also requires an effective heat transfer area, so in general, proper roughening of the outer wall of the radiator can increase the effective heat transfer area; In addition, when spraying different colored paints, need to consider the thickness of the spray and the thermal conduct ability. Generally, in order to increase the heat exchange area of the radiator, we use the fin structure, of which effective heat exchange area is about 50%-60%, and the "fin-type" heat sink can adjust effective heat exchange performance by change the heat conductive efficiency and fin spacing.

In the natural convection system, the power supply of most LED lights like tube light, bulbs and spotlights is generally placed inside the lamp cavity and the power supply will also generate heat, it is recommended to increase the air layer between the power supply, the LED light source and the bonding platform of the PCB to form an air partition and weaken the thermal field superimposition effect.

3) Heat radiation

Heat radiation is a transfer method that allows heat exchange to occur without any medium or without any contact.

In addition, thermal radiation is a kind of energy transfer that all objects are carrying out at any time, and the radiation intensity of different materials is different. Generally, the radiation intensity of cold-colored objects is lower than that of warm-colored objects, and the radiation intensity of rough objects is greater than that of smooth objects. Generally, the radiant heat exchange of bulbs and spotlights is small and can be approximately ignored.