Where do all the photons go

Where does light come from and where does it go?

Spectral lines of an LED lamp. We see very well the few energy differences that show up as lines (colors).

Light is created in light sources. Strictly speaking, in the atom. Strictly speaking, in the shell of the atom. An electron is in the excited state in the electron shell. It reverts to its basic state. The energy difference is emitted as "light quantum", the following applies: E = hf, and that means: Energy difference (E) = Planck's quantum of action (h) • Frequency of light (f)

For example, light disappears in a black cat. A ray of light hits their fur. To an atom of their fur, more precisely: it meets an electron in the shell of the atom. This electron goes into an excited state. The “light quent” has been absorbed, light has disappeared, the cat has absorbed the energy and has become a little warmer again. Again the relationship applies: E = hf. The energy absorbed is proportional to the frequency of the light. the greater the frequency, the greater the energy.

Does that also mean something for my life?

Absolutely. The higher the frequency of the light, the more energetic it is. Sunburn from UV light (ultraviolet). The frequency of the UV light is so high that the energy is sufficient to knock an electron out of its shell. This ionizes the atom. If this atom is in the genome of a living being, it can be changed as a result. Skin cancer can be triggered.

And what is light actually?

Light is an electromagnetic wave, like radio waves, only with a higher frequency. The retina in our eyes is sensitive to these frequencies. In quantum physics, one also speaks of the fact that light consists of a stream of particles, the "photons". There are so-called - indivisible - energy quanta that carry the energy portions E = hf. Overall, one speaks of the “wave-particle dualism” of light. Some experiments can be explained well if one assumes that light is a wave (interference), some can be explained well if one assumes that light consists of particles (photoelectric effect).

Still interested?

One episode of the Physical Soiree deals with light, its properties and how one can get to know light. Link to conversation.