Very cool project! Do you have a budget?
This is a BIG project, but I wouldn't say it's "complex". If you can build one pressure-activated light-cell, you can build 100 or 300. You could do some interesting things with a combination of pressure sensitivity, music triggering, random (and not so random) pattern generation etc. Once you have a matrix, there's a lot you can do. (BTW - The dance floor for Saturday Night Fever
was operated manually behind the scenes.)
My gut feeling is that jwatte is about right with 1/4" lexan (polycarbonate), assuming an unsupported square size of about 6". We seem to be using American measurements & dollars... Are you in the U.S.? From Tap Plastics, it's about $14 per square foot.
A strain gauge seems like the "obvious" choice, but from what little I know about them, I think
they have very low-output and you'd need lots of amplification. It's not hard to get amplification with an op-amp, but with low signal levels you can get noise problems, and the setup just might be finicky. I was looking around to see what I could find, I found some Force Sensitive Resistors
. Or,you might be able to do something with short-travel tactle switches, but I'm not sure... I think you'll have to do some experiments to see what works for you. Again, you've just got to design & perfect one cell and then duplicate it a couple hundred times...
I'm not sure if LEDs are the obvious choice. This is what I'd call a "Major Effect" and you probably want LOTS of light. You can get more light for less cost with incandescent. Also with incandescents, you can screw-in a larger (or smaller) bulb if it turns-out that you want more (or less) light. At low power, the driver circuits are cheaper for LEDs, but with high power LEDs the driver circuits can get expensive. So, I think an optoisolator and TRIAC switching AC voltage is probably cheaper. On the other hand, if this thing is going to be portable, incandescents might be too bulky and might need too much power for something that has to plug-in along with your other sound & lighting equipment... I've got about 1000 Watts of lighting, and I have to be careful about adding anything else (like a fog/haze machine) because I could blow a fuse.