Yes, light can affect materials in a great many ways. The most trivial
effect is that the photons can bounce off and you can see them. Most
metals work in this way, as mirrors. Most materials absorb some colors
of light and reflect others, to varying extents, so that they are
colored. Some materials will even absorb light of one color and re-emit
light of another color, an effect called fluorescense. Shine a "black"
(ultraviolet) light on some fluorescent materials and the materials
will appear to glow.
Some materials store up light energy and emit it later.
Glow-in-the-dark stuff glows like this. Electrons are excited to higher
levels of energy in the material and take sometimes minutes or hours to
decay away.
Many materials just get hot when you shine light on them, and some
will melt if you shine enough light on them (ice, wax,..). Some
materials, like some inexpensive dyes, will "bleach" in sunlight --
they will lose some of their pigmentation and become more whitish.
Some special materials will even generate electricity when you
shine light on them, like semiconductor solar cells. Some materials
will emit electrons when hit with photons.
Plants even use the light energy via photosynthesis to manufacture
foods the plant needs, at the same time generating oxygen and consuming
carbon dioxide and water.
But maybe you are interested in the momentum that photons carry.
This momentum is very small and it takes quite a lot of light and a
very delicate apparatus to even be able to measure an effect of it.
Tom
(published on 10/22/2007)
