Electronic – How to manage a large array of “motion sensors” and lights

You could look at triggering different lights with amplitude, like a VU meter. This is a cheap 5 LED digital VU meter ->

http://www.littlediode.com/components/LB1403N_LB1403_Integrated_Circuit_.html?NO_COOKIE_WARNING=2&ti=646e9cc97c539a96ef3257fa2cc49a19&xid=5c2ec922e32bf8c66047b98f481d025f

I've used it before to drive some LEDs on a kinda birthday card thing, I plugged the card into my Ipod output, and the 5 LED flowers on the card flashed with the music!

You could hook the output pins to some transistors which could then drive your colored light bulbs, it would be much cheaper and easier than using a micro controller. This would give you a regular audio level meter much like the one on a mixing desk, you could however change the order and color of the lights to mix it up a bit, so it's more of a light show. The lights also fade in with the increase of amplitude rather than just flashing on at a set value, so it would look cool.

Otherwise you would have to take a look at frequency analysis, whereby the lights could be triggered by the audio level at different frequency bands (one per light). This system would closest resemble a disco light that flashes with the different instruments in an audio track, but it's much harder to implement when compared to amplitude analysis. I'm sure a modern MCU would do the job with ease tho, with only 5 lights the resolution on the analogue inputs would not be a huge issue. If you could find some code to steal this option wouldn't be that hairy, if you're familiar with micro controllers.

If you choose synchronous detection, then you can simplify solution. Then you may want to choose LEDs as narrow angled as you can withing any part of visible spectrum.

Synchronous detection is the way to detect a signal which may be lower than background noise. Imagine taking shot with camera before LEDs are up. Then turn LEDs on and take another picture with exactly same conditions. Subtract arrays of pixel values of 2 frames from each other and look at the remainder. It will contain perfect difference of what was lit by LEDs. In your setup the DIFF picture will contain exactly retroreflectors (cataphote) only. Because the rest of the scenery got no significant increase in brightness.

While you debug the solution it will be obvious that power of LEDs can be reduced to some very low level, but only experiments will tell. I estimate that you will not need any super-powerful diodes. Some ordinary white LEDs with very acurate lens will do.