camera feedback problem - iSight surgery?

Hi,

I'm trying to improve my installation-setup, which suffers from a major camera-feedback problem.

My installation consists of 48 tubelights which are controlled (using dimmers) by people walking in the space.
I'm using an isight for tracking the movement, mounted on the ceiling (the cam doesn't see the lights)

This all works fine on a sunny day, the problem arrives when the space becomes too dark, and all the pixels respond to the changing lights (which the floor reflect).
I tried thresholding the framedifference settings, but it's not sufficient.

I'm desperately looking for some advice.

I'm considering to remove the infrared blocking filter from my iSight and start using strong IR-lights.
does anybody have experience trashing iSights?