Simplify KE->Temperature calculations

No need to calculate average KE using 

   (2 / 2N) * totalKE

when it's quicker to just do

  totalKE / N

and visa-versa.
Fix buggy implementation of emitLightSourcePhotons timer

Math.floor(time % 1000) can happen 2-3 times in a row, since
dt < 1, so duplicate photons were being emitted each time.

[#56363226]
Thiner, lighter version of photons

Dark black photons were visually overwhelming.

[#56363226]