COOLING LUXEON STAR LEDS

HEATSINKING and COOLING HIGH POWERED LEDS

INCLUDING 1 WATT 3 WATT AND 5 WATT LUXEON STAR LEDS

Preface:

It seems these days there are either those who fret over how to keep their leds cool, or those who ignore things and run them too hot so as to cause shortened lifetimes and reduced brightness. There is no reason to make things overly complicated or overly engineered, nor is there any reason to not use a simple easy to implement heatsink to keep them cooler.

My thanks go out to a nice engineer at Aavid Thermalloy, makers of the worlds finest heatsinks. He set me straight about heatsinks.

Its surface area - Its surface area - Its surface area

Please do not confuse surface area with mass or weight. A heatsink should be lightweight aluminum, and either a large flat surface, or a smaller finned heatsink, or pin grid heatsink. Anything more like copper or fancy water cooled schemes might be useful, if you have no way to increase the surface area or the airflow across the heatsink

Did I make my point? You can use a nice Aavid Thermalloy black anodized aluminum pin grid array heatsink designed for Ball Grid Array IC's like Xilinx FPGA's. They work perfect - lots of surface area sliced up into a nice small 1 inch by 1 inch by 3/4 inch package. Want to make it better? Make sure some air moves across the heatsink. Use a small fan if need be. It makes a HUGE difference. So far we know we need surface area, and air flow to keep the leds cool.

When I stated mass or weight was not important, let me illustrate my point: - 2 pieces of aluminum - each one is 6" x 6" square - one is 1/4" thick, the other is 1/16" thick......which one cools better.....they both due essentially the same job at cooling, yet one is less expensive, because it is lighter, and because it is lighter, it is therefore, more malleable, meaning you can easily bend it into whatever shape you want. In fact, you can make your heatsink out of thin gauge polished aluminum, bent into any shape you want, and use the heatsink, as the reflector as well. If you need to mount 5 or 6 one watt leds in a row, simply use a 16-18 gauge strip of aluminum the length you want the leds spaced apart, and 2-3 inches wide. Its that simple. Or you can simply use any old cpu heatink out of an old computer for most 1 watt applications. If you keep the fan in place and power that as well, you can easily keep a 3 -5 watt star cool enough. remember, if the heatsink was designed for a 20 watt device when the fan is running full tilt, it will certainly keep a star cool.

If you have lots of old cpu fans to rummage thru, you might even find a fan/ heatsink combo that can share the same power source as the led, and keep it cool without being too loud. We have tested several combinations that worked fine, as well as several that didnt.

The main thing is to keep the leds reasonably cool. What is reasonable? To me, reasonable is it never gets so hot that it could injure someone. In our tests with a temperature probe and our own hands, we determined that 114 degrees F was very warm, but torerable without long term damage. At 120 degrees F , we wanted to let go after a few seconds. The manufacturer states that the brightness ratings are at 25 degrees centigrade. Thats room temp. Its not 114 to 120 degrees. So at 114 to 120 degrees your leds are suffering some, and above that suffering even more, leading to premature failure.

So where does that leave us? Put your leds on a big enough heatsink. Whether thats a Finned - Pin Grid Array - CPU heatsink, or just a plain old flat piece of aluminum. If its too hot to hold, if you wouldnt want a 1 year old baby held up against it, its too hot. If you can hold it in your hand after 5 hours at full power, thats good, if its just slightly warm after 24 hours, thats great. A 5 watt luxeon star, mounted to a 6.5" x 6.5" piece of 18 gauge flat aluminum stock, exhibited nothing more than a slight warming sensation over most of its surface, and directly behind the 5 watt device was only slightly warmer, certainly not over 85-90 degrees F. Imagine if this were exposed to even slight air movement it would be even more efficient. Think of a heatsink for leds, as being like the radiator on your car. If your radiator quites working, eventually your car dies. If your leds get too hot for too long, eventually they die an early death as well.

So whatever you do, keep your leds as cool as possible, either with a brand new manufactured heatsink of sufficient size, an old CPU heatsink out of an old compueter, or make your own from simple lightwight aluminum sheet stock.

( And forget about anyone ever saying 100,000 hours lifetime for leds, cause it aint so unless you ran than at half current and kept em in a freezer)

Questions - Errors - Corrections - Help - Praise - Advice?

email sales@moreleds.com