system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Are lightwaves around us even when it's dark? If not, where exactly do they travel from when a light is turned on?
gpt
Light moves really fast.

When you turn on the light switch, the light source will send out light everywhere and they will reach your eyes before you notice.

Light sources usually produce light either by running a current through a small string of metal, heating it until it glows white hot or by pushing electrons through a diode which will turn the energy into light.

Once the light leaves the light source it goes everywhere, reflecting of walls and ceiling and the floor and all objects in the room, it will also be deflected by the air in the room, lighting up parts somewhat that would otherwise be in total shadow.

This happens too fast for you to notice, so the moment you turn a switch there is light everywhere.

Regarding light waves being around in the dark, it depends a bit. Obviously darkness is the absence of visible light, so there is no light when it is dark. However it rarely is totally dark, there is always some tiny bits of light getting in unless you take extreme measures to ensure darkness.

There is also the question how you define "light" light is just part of the electromagnetic spectrum and the same sort of thing as radio waves, microwaves, x-rays and gamma rays. You just call them by different names depending on the frequencies. Many frequencies of light can travel as easily through walls as light can travel though a glass window, so those will be around even in a dark room.

Even worse everything gives of some light by virtue of not being at a temperature of absolute zero. With objects the temperature of a normal human living human body that is in the infra-red range. It is too far in the direction of red on a rainbow for humans to see. The higher the temperature goes the more the color shifts into the visible range until you have something hot enough that it first starts to glow a dull red and then a hot white.

So even in the dark you usually have some tiny amounts of visible light and the invisible light giving of by everything. This is how night vision google work. Either they take the tiny scraps of light that there are and amplify them so that your eyes can see them or they shift the invisible infra-red light up a bit into the spectrum where you can see it.

Even in the dark.