Welcome, apobene, and good luck in your endeavors. I once dated one of your countrymen. He was from Ismir. (Aside:
I special-ordered a bottle of Izmira, which is vodka if I recall correctly, as a present. He was delighted to have it again, and said at home they drink it mixed with beer.)

Now, your query: by "essence" of light, do you mean what it is or what it does? Light is a form of energy, but it shines. I humbly offer this post as fodder for those more knowledgeable to pounce gleefully upon... with the caveat that I interpreted his question as wanting a good mental image of light, not a scientific
description.