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If a cave had 1 mirror at the mouth receiving sun, and a relay of mirrors going down into the cave, how far could the light travel?

Would the mirrors need to heat up to push light further?

If a cave had 1 mirror at the mouth receiving sun, and a relay of mirrors going down into the cave, how far could the light travel? Would the mirrors need to heat up to push light further?

(post is archived)

[–] • 7 pts

Inverse square law. Light decreases at the square of the distance. If your light source is 1000 lumens at 10', it'll be 100 lumens at 20'. Light can travel arbitrarily long distances (literally across the universe), albeit decreasing in strength. Additionally, typical mirrors are only 90% reflective, so that's additional loss with each mirror you add.

Human visual acuity varies by wavelength. It's best for blue-green light, worst for red. For ideal wave lengths, humans can detect as little as 1 photon.

There's also some scattering based upon atmospheric density (pressure) and particulate matter (smoke, haze, etc).

The TLDR is that your light will be visible in any real cave no matter how faint. Setting aside hypotheticals like 100 light year long caves with single photon light sources at one end.

[–] • 1 pt

That's the smartest answer to a dumb question I've seen in a while

[+] [deleted] • 2 pts
[–] • 1 pt

This is a very question.

Just sayin.

[–] • 0 pt

He's likely to ask it or likely to answer it well?

[–] • 0 pt

He asked lots of stupid questions. Constantly.

[–] [deleted] • 1 pt

Heat up? What?

The light would reflect a considerable way before it started to diffuse depending how much direct light the first mirror reflected and how clear and big each mirror was.

With the right shape mirrors you could light up as much of the cave as you want. It's sunlight. It has the legs!

[–] • 1 pt

Wouldn't the light heat the mirrors some? Wouldn't that heat steal some of the light's energy?

Or are you saying the light could bounce 5 billion times with no degradation?

[–] • 2 pts

Most of the heat would be from the infrared spectrum if you're using standard mirrors, glass is opaque to IR.

[–] • 1 pt

Did not know that, thank you

[–] [deleted] • 1 pt (edited )

Most of the light hitting a mirror is reflected. They warm up a little bit over the day but if you have a well made surface then yeah, whats stopping light from travelling 5 billion miles to earth and then a few miles around a cave? Diffusion/degradtion is your problem. The first mirror will beam a nice amount of light that ideally you'd used to light up an entire cave from the roof.

[–] [deleted] • 0 pt

Oh man, did this hit such a nerve that this guy deleted his account?

[–] • 1 pt

The shame of editing got to him

[–] • 1 pt

You'd never make it to the platonic forms