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LED Heat Management

Posted: 2013/05/27

Have you ever felt your head get hot while standing under a spotlight? This is because traditional incandescent lights emit much of their energy as heat (IR waves) instead of useful light. Light emitted by LEDs, however, has been dubbed "cool" because LEDs turn much more of their consumed energy into useful white light, contributing to their much touted high efficiency.

A thermographic image showing the amount of heat emitted by various types of lighting. Clockwise from top: incandescent, compact fluorescent, and LED.

The photo above shows where heat (shown as yellow, red and white regions) is emitted - it is quite obvious that both the incandescent (top) and CFL (bottom right) lights emit a significant amount of heat outwards. The LED (bottom left), however, releases very little heat in the direction of the emitted light.

This is a very useful benefit of using LEDs, particularly in places where objects can be damaged by prolonged exposure to heat and IR radiation. If conventional lighting is used, in uses such as in store displays, the products or packaging can be damaged. Even in supermarkets, LEDs are a better alternative because perishables can spoil under the heat. LEDs can even help cut down on air conditioning costs.

If you look at the above thermography photo, however, you will notice the significant amount of heat being released below the hemispheric portion of the bulb. LED bulbs do not emit heat in the direction of the light, but they nonetheless emit heat.

One of the main reasons for premature LED light failure is overheating, and dissipating this heat away from the LED chip is in fact a very important topic in LED technology development. In short, as electric current is ramped up in order to generate brighter lights, more heat is generated. With increased emphasis on brightness and efficiency, allowing heat to be released to the ambient environment with the least resistance possible allows for the most successful heat management solution.

LED chip, where the PN junction is located, not all electricity is converted into visible light. Some of this energy is released as heat, and in order to preserve the LEDs' lifetime, the heat must be wicked away either through conduction, convection or radiation. Therefore, the epoxy used to mount the LED chip, and also the encapsulation epoxy covering the LED chip must be able to conduct heat in the most efficient manner possible. These epoxy and silicone materials measure thermal conductivity in watts per meter kelvins, with the best types reaching up to 8.0 W/mk.

A CFD analysis image showing temperature-color coded flow trajectories of an LED light bulb. Source

Heat sinks with many fins and grooves (see below) aid in releasing heat to the ambient environment. Factors affecting the performance of heat sinks include the material, shape, surface finish, and mounting method.

Examples of various heat sinks that wick heat away from the LED chip. Aluminum is the most common material used.

Additionally, the physical design of the LED light can affect the heat management performance. In relatively compact designs such as spotlights, for example, there is less area to dissipate the heat, so either longevity or brightness must be compromised. Additionally, ambient temperatures for outdoor lighting must be thoroughly considered as well.

Specifically, how does the heat affect the performance? There are cases of LED lights failing, dimming, or changing color only after 1000 hours of use, which defeats one of the original purposes of superior LED lifetime.

Relative brightness of various colors changes at different temperatures. If an LED light is allowed to over-heat, the emitted colors can be different from what is intended.

A chart showing how temperature can significantly affect the lifetime of an LED.

We at Beijing Yuji place special emphasis on identifying product designs which allow for effective heat dissipation in order to guarantee maximum longevity and performance. There are many products in the market with poor heat management technology, therefore, we highly recommend that you please contact us so that we can ensure that we supply you with products that last as long as actually promised.

Author: Alex

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