Dimming LED lights with PWM, driver quite far from LEDs, noise considerations
The inductance of the wires will create voltage spikes -- be careful for your drivers. In any case, they may not be able to regulate the current in a stable way with large series inductances.

Likely AM and TV will be the worst affected (all below 100 MHz), but cheap radios may get swamped with the interference. 

Is the reason you are using PWM because you want precise colour ? If you can accept small colour variations, then DC (variable current) drive would be much better as far as emissions are concerned.