Yes! In fact there is a new paint that was developed with exactly this in mind. https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest...

Reflects 98.1% of the suns rays.

Aircraft can safely fly over snow, which has albedo if 90%, so it's probably ok.

Only if the roof has a lens shape, otherwise it's the same light as what's coming from above which isn't harmful.

well, it's 98.1% of the same light, so technically, less harmful

If the roof scatters the light, probably not.

However if an entire downtown or subdivision does it? Possibly.

Trees, trees are a much better solution. Very simple yet effective solution to urban heating problem

https://creativelyunited.org/wp-content/uploads/2019/02/temp...

That street's sin is not the lack of trees, but having 6 entire lanes for cars, which apparently all go in one direction. An uncrossable nightmare that only even has stores at one side!

Those nice trees take a few decades to grow, need serious pruning, will cause foundation problems next door, and increase building setbacks anyway. We also waste two entire lanes for street parking, have basically no businesses on either side anyway, and the street is still too wide. It might be urban, but it's still a car centric hellscape, just with some shade.

Yes but not on roofs. They're so heavy.

Aren't grass-like plants working reasonably well? It's quite common on new build where I am

"white" and "mirror" are equally good at bouncing light, and the exact effectiveness is based on the specific design.

Please explain? Mirrors seem to reflect much more, but maybe that's another effect.

That's an illusion because from certain angles the mirror is much brighter, and you don't pay as much attention to all the angles where the mirror is darker.

An ideal mirror reflects 100% of the light, and so does an ideal white surface. The white surface just spreads out the light.

If you light a mirror evenly from all angles, it will be indistinguishable from a white surface.

Thanks. That was my first guess, that it was directional.

Not if you want to use the sun’s energy for power

You can do both - having solar panels over a reflective white roof (like the fancy newly discovered passive radiative cooling paints) helps increase PV output by cooling the panel.

The solar panels will still absorb and radiate heat back so you won't get as much cooling as you would have just with passive radiative cooling paint, but it'd be better than just solar on a regular roof in both ways (solar output and thermally).

Thermal radiation is just EM waves, which you can reflect.

So just put the PV panels on top, and a reflective layer below.