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Can someone explain the difference between this and a mirror? A mirror reflects also something like 98%, right?

buran77 6y ago
I would expect it's twofold. This paint acts like a "diffuse mirror" so doesn't create any bright spots like specular reflection. This is great particularly in cities where every building would become a giant mirror. On the other hand a mirror finish is harder to achieve on rough surfaces that the paint would presumably be used on.
- Arnt 6y ago
  Adding: Mirrors don't have to reflect very much, they have to reflect as a picture. That's why one-way mirrors work — people generally don't notice that the light mirrored is much less than 100%. White paint is free to reflect the photons in any direction, so that >98% is a harsher requirement on the share of incoming photons, but a laxer requirement on the photons' direction.
  - buran77 6y ago
    Some mirrors can reflect a lot more light even if in narrower wavelength ranges. But that only makes the matters worse from a practical human perspective, when trying to use them on large surfaces outside. It would feel like staring into the Sun far too often.
    - Arnt 6y ago
      Which mirrors are that, and why are they made, what are they used for? Just giant telescopes on remote mountaintops, or is there more?
      - buran77 6y ago
        Lasers! :) I'm talking about dielectric mirrors. Wikipedia suggests 99.999% or better reflectivity over a narrow range of wavelengths.
        Arnt 6y ago
        Of course. Duh.
cigaser 6y ago
Aluminium coating (most mirrors) only reflects between 80% to 90%. It reflects light in single direction. White paper reflects more, but scatters light in several directions.
mrob 6y ago
A mirror reflects with specular reflection. When parallel rays of light hit a flat mirror they remain parallel after being reflected: https://en.wikipedia.org/wiki/Specular_reflection https://en.wikipedia.org/wiki/Specular_reflection Paint reflects primarily with diffuse reflection. The rays of light are scattered in all directions: https://en.wikipedia.org/wiki/Diffuse_reflection https://en.wikipedia.org/wiki/Diffuse_reflection
- appleflaxen 6y ago
  That's an awesome learning point; thank you. What percent of the light does a mirror reflect in a specular way?
  - analog31 6y ago
    Like the design of paint, the design of a mirror can affect its reflectivity. For an extreme example: https://www.semrock.com/maxmirrors.aspx https://www.semrock.com/maxmirrors.aspx Mirrors that are a cheaper coating on glass or metal can be in the 95% range without too much effort. If you don't care about actually forming an image with a mirror, it can be quite cheap, e.g., plain aluminum (with whatever oxide forms on its surface) or aluminized mylar film.
- snug 6y ago
  I was going to ask this same question, thinking it would be a dumb question, glad this got answered! Thank you

I would expect it's twofold. This paint acts like a "diffuse mirror" so doesn't create any bright spots like specular reflection. This is great particularly in cities where every building would become a giant mirror. On the other hand a mirror finish is harder to achieve on rough surfaces that the paint would presumably be used on.

Arnt 6y ago
Adding: Mirrors don't have to reflect very much, they have to reflect as a picture. That's why one-way mirrors work — people generally don't notice that the light mirrored is much less than 100%. White paint is free to reflect the photons in any direction, so that >98% is a harsher requirement on the share of incoming photons, but a laxer requirement on the photons' direction.
- buran77 6y ago
  Some mirrors can reflect a lot more light even if in narrower wavelength ranges. But that only makes the matters worse from a practical human perspective, when trying to use them on large surfaces outside. It would feel like staring into the Sun far too often.
  - Arnt 6y ago
    Which mirrors are that, and why are they made, what are they used for? Just giant telescopes on remote mountaintops, or is there more?
    - buran77 6y ago
      Lasers! :) I'm talking about dielectric mirrors. Wikipedia suggests 99.999% or better reflectivity over a narrow range of wavelengths.
      - Arnt 6y ago
        Of course. Duh.

cigaser 6y ago

Aluminium coating (most mirrors) only reflects between 80% to 90%. It reflects light in single direction. White paper reflects more, but scatters light in several directions.

mrob 6y ago

A mirror reflects with specular reflection. When parallel rays of light hit a flat mirror they remain parallel after being reflected: https://en.wikipedia.org/wiki/Specular_reflection https://en.wikipedia.org/wiki/Specular_reflection Paint reflects primarily with diffuse reflection. The rays of light are scattered in all directions: https://en.wikipedia.org/wiki/Diffuse_reflection https://en.wikipedia.org/wiki/Diffuse_reflection

appleflaxen 6y ago
That's an awesome learning point; thank you. What percent of the light does a mirror reflect in a specular way?
- analog31 6y ago
  Like the design of paint, the design of a mirror can affect its reflectivity. For an extreme example: https://www.semrock.com/maxmirrors.aspx https://www.semrock.com/maxmirrors.aspx Mirrors that are a cheaper coating on glass or metal can be in the 95% range without too much effort. If you don't care about actually forming an image with a mirror, it can be quite cheap, e.g., plain aluminum (with whatever oxide forms on its surface) or aluminized mylar film.
snug 6y ago
I was going to ask this same question, thinking it would be a dumb question, glad this got answered! Thank you