[dheera]

I don't think 50000 60-ft mirrors at the height they intend to fly would cause that to happen. Not enough light gathering power.

50000 60-ft mirrors is about the same area as a single mirror 2.5 miles across. So the area of the mirrors is about the area of a city. You gather as much light as the city itself in regular daytime. If you focused all of that perfectly efficiently onto a city, that city would just look like daytime.

[etskinner]

I think what you're missing is that they could all be focused in one spot, not spread over the city. If curved reflective buildings can melt siding, and mirror solar plants can melt salt, I'm pretty sure a city's worth of sun focused on, say, a college campus, could start a massive fire

[dheera]

I see your concern. The mirrors could be deliberately manufactured to have enough imperfections, or slight reverse curvature, to prevent this. It's possible with properly-designed optics to prevent the mirror from being able to focus on a spot smaller than, say, 1/50000 the mirror's area on the Earth's surface. Make each single mirror only optically capable of focusing down to a 3-mile diameter at best. Then it would be optically impossible to focus all the mirrors to a single 60ft spot, and the theoretical highest brightness at any point on Earth would just be regular daytime levels of light.

[Cthulhu_]

I think people overestimate the relative strength of the sun.

Then again, assuming there's no dispersion or loss, 50.000 times the sun focused on a 60ft patch will likely have some impact. But that's complete fiction.