What is light ?

Even after all this bullshit about gravity dark energy, there are some fundamentals that are still a bit foggy and need to be clear, we talked a lot about light, its velocity, the doppler effect but we haven't talked about light itself, so what is light?

First of all, light is a wave and every wave has a wavelength which is the distance between two consecutive summits, so if the wave is compressed the wavelength is small and vice versa. But how light is emitted?

The answer is very simple, give something extra energy and it will discard the excess. From that, we can discern that the higher we give the greater we receive. Depending on the EM spectrum the lower the wavelength is the higher the energy, this can be translated by the equation E=h𝓥 /𝛌 where E and 𝛌(the wave length) are inversely proportional. 

But that's not as simple as that, Let's suppose that I decided to go upstairs, to do that I need energy and I have to go one step at a time, so if I don't lift my foot well enough I can't get to the next step, If I am in a hurry I can lift my foot for 3 or 4 steps which consumes more energy. This applies the same to the atoms, the electrons have specific levels of energy and to push them to go to the next stage we have to give them the exact necessary amount of energy we call that quantified energy, but that doesn't emit light! If the electron jumps from one level to another that means that it consumed the energy so there is no emission. Well, it's not the end of the story!

Every atom searches for the maximum level of stability which is nothing else than its natural form.

The electron doesn't feel comfortable in its new orbit and it's "Excited" to go to its original orbit.

The reversion causes a specific amount of energy to be emitted in the shape of photons which represents light. This phenomenon is very obvious when heating up an iron bar, the longer we heat the more energy we give and in consequence, the more energy we receive because atoms have returned from much higher energy levels this is manifested by the color swing from red, orange to yellow each consecutive color has higher wave lengths and therefore higher energy. 

Another important thing to mention is that every element has its unique energy levels, that's why we use different elements in lighting like neon, hydrogen or mercury light tubes: every element absorb different amount of energy so the emission differs as well, so if we calculate the emitted energy E we can define 𝛌 and by comparing it to the EM spectrum we can determine the color of light we will get!