Heres and interesting idea that got me thinking watching an episode of cosmos on Michael Faraday and hes experiment on light waves and magnetic fields .
I was surprised hes was able to do it .
I know these days its easy to modulate a laser but still not so easy for non solid state light this may well be a low tech way of doing it /
http://jesseenterprises.net/amsci/1970/ ... 11-fs.html
The filers are easy to make via 3D glasses this video shows you how the filters would work towards the end .
I think the light has to be of one colour for it to work.
http://www.youtube.com/watch?v=ObdcScUEICM