You could probably also use SMD UV but this would be limiting.
-A

(Grainy publicly viewable pic on facebook here: http://www.facebook.com/photo.php?pid=36475041&l=07175&id=61204497 )

This method produces very good results, and mine only needed a gap of around 5cm before the emitted light became even (with the particular leds I used).

In the true style of building something to make something else, I first prototyped this point to point wiring all these leds which had been affixed in a 12″ square piece of wood. They then exposed the boards that now form the actual light box :)

I went down to the local glass supplier to get two panes of 12″ square glass cut to sandwich the mask and board.

There is also a 128×64 graphics LCD cut into the top that gives a nice display, and a rotary encoder switch (with button press) to give all of the input required.

All this was run off a 5v 2A (but not using all 2 amps!) wall mounted transformer.

-Andy

I personally use an old mercury-UV-lamp at appr. 40cm distance.