Of course if you want full efficiency there is this:
http://www.linear.com/pc/productDetail. ... 1094,P1929

It uses a switching supply to drive the LED with a constant current so (in theory) all the power turns to light...

Yes, if you wired some of the leds in series then it's a lot more power efficient. More work though.

I'm doing this very thing. Here's how I'm going. I haven't finished yet but will update: - I pulled the flashlight (cheap $2 headlight) apart. It has a battery pack, a control board with a push switch and a board with 5 leds wired in parallel. - the push switch selects flash / steady / off and has a...

There are heaps of army surplus stores around the UK. Unfortunately since I no longer live there I don't know where they are. But www.yell.com is the UK yellow pages and will tell you.

(Sorry to be less than helpful, but I saw nobody else had posted at all).

Some laptops - like my work one, drive two independent screens. So you can have use the laptop screen for control and do other stuff on the projector.

Or you can get multi-output cards quite cheaply (not sure on macs though, but loads of designers have dual screens so it must be possible).