Where does light go when the light source goes off?

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I know this is probably a stupid one here.. But like, isn’t light just photons bouncing around? My lightbulb is firing these photons out when it’s switched on but presumably it’s not sucking them back in when it’s off?

So where da light go?

Also shouldn’t it get brighter the longer the light source is on as there’s more photons?

Where are they all going?

In: Physics
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they get absorbed. light gets absorbed, thats why you have colours and stuff and everything isn’t just different shades of bright.

since these materials absorb light they gain energy which is why if you shine a light onto something it will become (somewhat) warmer.

a few materials (like glow-in-the-dark-stickers) emit some of that “stored” light over time.

but mostly your light just bounces around a few times and gets absorbed a bit with each bounce.

It goes into everything that you can see. Anything black absorbs nearly all light that hits it, anything red absorbs all light except red light, etc. Even white things and mirrors, that mostly reflect light, absorb a small amount. This means that almost immediately after light stops being emitted, it is absorbed into your room.

Photons don’t bounce around as much as they are absorbed and re-emitted. But there’s some loss each time this happens, as heat. So the last photons that are emitted before the light shuts off are (slowly, from their perspective, but almost immediately from ours) absorbed, some re-emitted, absorbed, some re-emitted, and so on until they’re all gone.

> So where da light go?

absorbed.

> but presumably it’s not sucking them back in when it’s off?

Kinda but not really. Technically, yes, your light bulb is sucking them back. But the complete picture is that everything else in the room also suck it up.

Whenever light hits something, 3 things happen:

1. Absorbed

2. Reflected

3. Transmitted

If you have window or anything transparent (even by a little but), then the light are transmitted (basically goes through), so that’s one way the light are disappearing.

Most surfaces reflect light, but not 100%, not even close. They usually absorb some of the light as well. That’s where the light is going.

I think you are imagining that the light gets 100% reflected by all surfaces, which is not true. In fact, this is why some people are asking questions like, what if you have a room of mirrors, then the light will bounce forever, but no. Even mirror absorbs light.

It depends on what materials you have around you. Some amount of light will be reflected off a surface, and that is what allows you to see that object. You see that fraction of the light that reflected, and went exactly in the direction of your eye. Some amount of light will be transmitted through a surface, and that is what allows people outside to see the light in your room. These processes are insanely fast though, so once the bulb is off, they stop almost instantaneously. Some amount of light will be absorbed into surfaces in the form of heat. These are the waves that are not enough energy to excite an electron, but are enough to increase molecular vibrations. If you have any glow-in-the-dark surfaces lying around, a much slower process known as phosphorescence may occur for a long while after. The molecules in these materials have an excited state that is much more stable than those of the reflective surfaces. So they become weak emitters of light themselves, decaying only as quickly as they are allowed to return to ground state.

>I know this is probably a stupid one here

This is not a bad question at all, I used to ask this to myself all the time when I was a kid, when I didn’t even know what photons were, so it was even harder to understand.

So imagine you’re fitting a gun. The gun being the source is light and the bullets being the photons. Let’s just assume for the sake of this example that the bullets travel for ever, till the end of the universe.

So if you stop firing (like switching a light bulb off), the bullets keep travelling. Your firing or not doing so doesn’t effect the bullets.

And just like bullets from a gun, even photons are released with a momentum, so they also never stop.