Step 4: Selecting the LED's
The Luxeon LED's are available in a couple of formats - the most useful is the "star" format which has the LED already attached to a small heatsink. this is far easier to work with than the bare LED.
The Luxeon LED's come in both "1 watt" and "3 watt" stars. the difference between these is actually a lot less than the names indicate and they are priced nearly the same also (about $3 each). in reality, my tests show that with a large heatsink the "1 watt" model is capable of 3 watts output, while the "3 watt" model is capable of 4 watts. the "1 watt" model is notably very conservatively rated, it is really more like a 2-watt LED. the caveat is: the LED's efficiency drops with increased power (2 watts gets you about 65% of the light output of 4 watts), and lifetime may also be reduced (they are rated at 50,000 hours though). so if you are making a light for occasional use and want maximum output for the $$$, feel free to run the LED's considerably over spec. if you want an efficient room light for long-term use, stick to 2 watts on the 1 watt model, and 3 watts on the 3 watt model.
the other important difference between the 1 watt and 3 watt stars is that the 1's have an insulated heatsink, while the 3's do not - that makes the 1's a little easier to work with since you can mount them directly to a heatsink. the 3's require using an electrically insulating film between the star and the heatsink. (see the step on heatsinks).
- do you want a spotlight or a room light? if you want a room light, get the "batwing" or "lambertian" LED's. these shine light over a wide angle (either 110 degrees or 180 degrees).
- if you want a spotlight, you can get the "Star/O" model which has a built-in lens. or you can get the regular batwing model and buy a separate lens for it which easily glues on. There are several companies making very inexpensive ($1) lenses for the Luxeon that let you make a 5, 15, or 25 degree angle spotlight. I've used these ones: L2Optics/Dialight part numbers OP-005, OP-015, OP-025, and lens holder OH-ES1 or OH-S35. Try this: direct search at Future.
- equalizing brightness/hue: the different color led's are not all equally bright at full power. the simplest light (shown in this project) uses one string of LED's in each color, so when you turn all three colors on full power, the overall hue is yellowish (*very* warm). that's because the blue led's are not as bright as the other two. so if you are building a larger light, consider using an un-equal number of strings of the different colors. if you use the Luxeon-1's, try 2 strings of blue for each string of green and red. with luxeon-3's, equalized-brightness requires using 4 strings of blue, 2 strings of green, 1 string of red. this is only important if you are mostly using this as a white/off-white lamp. if you are using it for an FX lamp, there is not much point to equalizing the brightnesses.
what I used:
I used 1-watt star LED's for my light (running them at about 2.5 watts each) because I had a bunch of them already, i'd recommend using the 3-watt stars if you are buying new ones since they cost nearly the same. i used 5 red, 5 green, 5 blue led's. part numbers:
1-watt: LXHL-MDAC, LXHL-MM1C, LXHL-MB1C.
3-watt: LXHL-LD3C, LXHL-LM3C, LXHL-LB3C
more information: the manufacturer datasheets:
Phillips Luxeon Star LED's: http://www.luxeon.com/pdfs/DS23.PDF , http://www.luxeon.com/pdfs/DS46.PDF
L2Optics/Dialight Lenses: http://www.l2optics.com/luxeon.aspx