Tuesday Night Ride Club (TNRC)

You want to concentrate it and hope that both light sources are kicking out light in the same wavelengths and phase, I'm guessing. Otherwise you'll have negative effects.

I'd ask this in "any questions".

Different wavelength would be fine and would not completely cancel. This all assumes light as wave (Huygens) rather than photon particles (Einstein).

I recommend 'In Search of Scrodingers Cat' as an easy to read text skimming the surface of both arguments and the duality where light is both a particle and a wave.