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Step 8Attach LED's to the heatsink
I used the 1-watt star LED's, these have an insulated backing plate so you just glue them straight onto the heatsink, no worries. if you are using 3-watt stars, you need an electrical insulator between them and the heat sink.
the "pro" way to attach components to a heatsink is: use thermal compound between the component and heatsink, add a special heatsink insulator layer if electrical insulation is needed, and screw down the component with nylon screws (or metal screws with a nylon bushing)
the "pro" way is a lot of work because you need to drill a lot of holes, and the special heatsink insulators are about $1 a square inch (let me know if you have a lower cost source!). luckily, the "pro" way is really a huge overkill here and we can do this much easier. why? the surface area of the luxeon star is large, and each LED is only about 3 watts. that's about 50 times less demanding thermally than a computer CPU.
so what's the easy way? we'll just glue down the stars using silicone glue. it works great. if you need a heatsink insulator, the best low-cost version of this is: thin mylar (polyester) film. most likely you already have some as reflective static-shielding bags, window-tinting film, or clear packing tape (although the glue on the tape is unsuitable, remove it with paint thinner). it is important to use mylar, other common plastic films will melt.
you need to use a flexible high-temperature glue, "GE Silicone-2" is ideal for this. press hard on the LED and squish it around a bit when you glue it down, you want as thin a layer of glue between the LED and the heatsink as possible & no air bubbles, to maximize thermal conduction. if you are using 3-watt stars, you need glue fully covering both sides of the insulator. use a little excess glue to make sure the entire contact area is glued (you can see where my glue is all around the sides of the LED after i squished down on the LED's).
- attach your LED's in groups of 3, each group has 1 red, 1 green, 1 blue LED. spread out the groups around the heatsink for best heat transfer.
the "pro" way to attach components to a heatsink is: use thermal compound between the component and heatsink, add a special heatsink insulator layer if electrical insulation is needed, and screw down the component with nylon screws (or metal screws with a nylon bushing)
the "pro" way is a lot of work because you need to drill a lot of holes, and the special heatsink insulators are about $1 a square inch (let me know if you have a lower cost source!). luckily, the "pro" way is really a huge overkill here and we can do this much easier. why? the surface area of the luxeon star is large, and each LED is only about 3 watts. that's about 50 times less demanding thermally than a computer CPU.
so what's the easy way? we'll just glue down the stars using silicone glue. it works great. if you need a heatsink insulator, the best low-cost version of this is: thin mylar (polyester) film. most likely you already have some as reflective static-shielding bags, window-tinting film, or clear packing tape (although the glue on the tape is unsuitable, remove it with paint thinner). it is important to use mylar, other common plastic films will melt.
you need to use a flexible high-temperature glue, "GE Silicone-2" is ideal for this. press hard on the LED and squish it around a bit when you glue it down, you want as thin a layer of glue between the LED and the heatsink as possible & no air bubbles, to maximize thermal conduction. if you are using 3-watt stars, you need glue fully covering both sides of the insulator. use a little excess glue to make sure the entire contact area is glued (you can see where my glue is all around the sides of the LED after i squished down on the LED's).
- attach your LED's in groups of 3, each group has 1 red, 1 green, 1 blue LED. spread out the groups around the heatsink for best heat transfer.
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Also, better adhesive isn't that much more expensive... a combination of some lousy-cheap PC heatsink grease in the middle and silicone on the outside is a great example of a different technique that might work better. It's really ok - no sweat if someone does it different...