Hi,
The principle is easy enough, I believe it's already been used (with fluorescent lights at low frequency) for supermarket "intelligent" (LCD) shelf-edge price displays. It's even easier to modulate the light output from LEDs, but the "dimmable" LED "bulbs" still seem to sell at a considerably higher price than the non-dimmable type. The brightness might be modulated by only a few percent and/or at very high frequency, so the eye will never see it. The average brightness can be constant because the data probably will be ac-coupled anyway.
However, even at 1 Gigabit/second (and most reports seem to be claiming 1 G
Byte/sec), light travels only around 30 cms (1 foot) so the "data" reflected off a wall will be out of phase with the "direct" path. Thus the modulation may need to be a scheme similar to that used for digital TV or DAB radio (COFDM). Certainly not PICAXEable; even dedicated DSPs seem to need lots of mA
and crash on a fairly regular basis.
But IMHO there are much more fundamental issues, what about the data "return path" (aka interactivity) ?. Also, an advantage of light is that it DOESN'T pass through walls and ceilings, so your TV Remote Control doesn't switch off your neighbours' TV, or the one in your bedroom. But that's not too good if you want to use your iPad there, probably with little or no main lighting switched on. And how does the "data" get to the room-lighting LEDs? Mains cables weren't designed for 1 Gb/B per second; "Powerline" comms. don't work well in my house AND they interfere with the Hi-Fi.
Cheers, Alan.