I believe you need a meanwell or buckpuck driver.. Look at Rapidled.com.. that should help
Ok thanks, that's what I was thinking would work. Now to track down resistors...You can drive the XR-E LEDs as low as 175 mA with no problems - my light fixture is set up to do that for "low" light. I suspect the problem is related to the driver producing more voltage than the drop across the 4 LEDs in series, which is about 12-14 volts. If you try a 2 watt, 20 ohm (or 22 ohm) resister in series with the LEDs, that should use up the surplus voltage. I can't say this will work, but it would be a cheap thing to try, and it won't damage the LEDs or driver.
I thought about that too, but considering how bad my current lighting unit is, anything's an upgrade. This is more of an exercise in just putting an LED system together in an existing strip light hood. It's $45 for a new hood/bulb, and so far, I've spent about $35 and I'm learnin stuff. As far as diffusion and spotlighting goes, you're probably right, but I'll see how bad it is before I get all worked up about it, gotta make the damn thing go first.A bigger question is whether 4 LEDs will give you enough light for a 20 gallon tank. I doubt that they will, and I suspect that you will have extreme "spotlighting" - 4 brightly lit spots on the substrate. You can look at this and see if it helps: http://www.plantedtank.net/forums/diy/84212-designing-building-led-fixture-22.html#post1102937
I think I got the wrong driver, as it's output voltage (18-43v) is way too high for 4 leds. I guess I was thinking 3w leds x4 in series needs a 12w driver. I'm not much of an electrical genius, that much I've come to figure out. So, basically is there any way to throw a resistor or regulator, possibly even a dimmer into the system with what I have so it works, or do I need to get a whole new driver and which one should I get?