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Beware the LED Killers – Over-Heating & Over-Voltage

LEDs are the greatest lighting source available, but in the RV environment they have two Achilles Heels — Over-Heating and Over-Voltage greenrecord.co.uk

LEDs are tiny slivers of semi-conductor material (p-n junctions for the geeks who want to know), a piece of silicon doped with rare earths that is mixed to emit photons in the visible spectrum whenever a proper voltage is applied across the junction such that an electrical current runs through the semiconductor. Like a true diode, LEDs resist letting current run in the wrong direction. The chemical composition of the p-n junction determines the wavelength of the emitted photons, so you can have red, amber, green, and blue LEDs, among others.

White LEDs are most often made using a native blue LED that shines blue photons into a phosper that in-turn re-emits a spread spectrum of light across a range that looks like white light to the human eye (for the geek, that is Stokes radiation).

Comparing regular lights to LEDs, the standard incandescent light bulb is only 15% efficient in converting the wattage into useful light. Fluorescent lighting is at best 50% efficient. LEDs have an efficiency of 85% or higher in converting the electrical energy into useful photons. This light source is the most efficient of all the choices we have for light in our RVs, boats, and homes.

None of our light sources are 100% efficient — there is always some residual heat. And it is the heat energy that destroys the light source. With incandescents, the 85% wasted energy is heating the filament to a temperature between 600 and 1200 degrees Fahrenheit. At those high temperatures the filament is literally vaporized away over time, most often within a thousand hours or so, and the bulb simply burns out.

LEDs, too, are heated by the flow of current through the circuit. LEDs will immediately fail when the junction temperature exceeds 185 degrees Fahrenheit. Properly designed LED circuits require two very important features to be successful: protection from over-heating and protection from over-voltage. Often the over-heating is related to over-voltage.

Even when an LED is operated at a carefully controlled voltage, it still generates some heat. This heat must be removed from the LED device at a rate that ensures the junction temperature does not exceed the operating limit. The best way to do this is to place the LED device on a “heat sink” that has the capacity to soak up the generated heat from the LED and move it to a place where it can be radiated into the air or some surrounding heat pit. Early generation LEDs did not bother with this problem since the printed circuit board they were used on was generally large enough to serve as a sufficient heat sink.

 

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