I think that infrared light is used because it is not "visible light" and so it does not make noise with it... so my idea is that visible light (from a light bulb) will not interfere with infrared light (and the dark room is just to make more visble the LCD screen under the plexiglass) but this is just my idea (and now is 2.00 am, so...). As an answer to quique, I would like to say that maybe is not necessary to write a pattern-detecting algorithm, as Jmyron already implements them. If it will be not sufficent, maybe we can use Eyesweb (http://www.eyesweb.org/), but it's use is out of my knowledge... :-/
cheers..
Corrado