How is thermodynamics related to optics?

Answer 1

The light you see results from a very complex yet simple process. Lets study that first.

When energy(supposedly heat energy) is transferred to atoms an electron(s) jump to a higher energy orbital but soon comes back down because it cannot remain that way forever due to thermodynamics(Everything in the universe tries to achieve a higher entropy). So it releases that energy in the form of photon(s). A photon is the smallest unit of life. It is the quantified state of light.

Now several electrons release several photons to form a beam of light. So the entire process requires energy transfer and conversion which is the basis of thermodynamics. I can provide more details but i think it would be better if you studied how light is produced in details.