This is very cool (or hot as the case may be), but I'm not exactly sure why being visible from space is stressed so much. The astronauts onboard the ISS don't look down at nothingness when they're on the night side of the world. Plenty of lights can be seen which aren't billion candlepower arc lamps.
From the ISS, the very smallest blobs you can see are 100 meters wide. There are very many large blocks of lights that can be seen from space. But to see a single light, it has to give a significant boost to the average brightness of an area larger than a football field. That's not very easy.
The size of area is not too relevant. The angular size of stars is very close to zero, yet we see them with naked eyes because they deliver sufficient energy flow. Pretty sure you can do that with just a few watts laser with size measured in millimeters, if you focus it well enough onto the ISS.
The area and angular size of the light itself doesn't matter.
But I'm talking about the angular size of the smallest detail a human eye can perceive, which does matter a lot.
Anything smaller than one arc minute might as well be a point source. A star is smaller than an arc minute. A light viewed from space is smaller than an arc minute. But either way, that "point source" has to be bright enough to light up the entire arc minute to stand out from its surroundings.
The only thing your eye perceives is the total light coming from that arc minute. Which is the same as saying you have to bring up the average brightness of that arc minute.
And an arc minute's area, viewed from low orbit, is somewhat bigger than a football field.
> Pretty sure you can do that with just a few watts laser with size measured in millimeters, if you focus it well enough onto the ISS.
Yeah but that's a laser. This is a white light. Much more difficult and impressive.
> And an arc minute's area, viewed from low orbit, is somewhat bigger than a football field.
This means if you take a point light designed to light a football field (football fields do have these light sources), and direct it into space instead of the ground, will be visible from low orbit.
> This means if you take a point light designed to light a football field (football fields do have these light sources), and direct it into space instead of the ground, will be visible from low orbit.
A point light designed to light up an entire football field should work, yes.
What football field has single lights that powerful? Normally you have many flood arrays with a dozen or more lights each.
> People did it with less powerful light sources:
Cool! So that's somewhere around one kilowatt, significantly easier to do.
Though notably it's still a spotlight. I wonder how many watts of flood light you would need.
> Normally you have many flood arrays with a dozen or more lights each.
I was thinking about a single array, from the orbit it’s pretty close to a point source.
> I wonder how many watts of flood light you would need.
I don’t know about efficiency of that military equipment (need beam angle to compute), but I would expect with modern white LEDs you don’t need that many watts, they’re very efficient at converting electricity to light. You would probably still want liquid cooling for them, though.
