Re: [APD] Re: ah supply reflectors

["S. Hieber" <shieber at yahoo_com>]

Don't know. Test were done back in the 70s -- lots of folks
doing indoor home gardening in those days ;-) -- and
tinfoil turned out to be the pits and flat white did better
than gloss.

Light reflection doesn't occur only from photons bouncing
off just at the surface -- the photons go into the material
and when they hit a particle at the "right" angle, bounce
back out. Many pass through the material (depending on the
material) and many/most are absorbed, causing lower energy
level (infra red) photons to be shed from the material. So
what a substance is made of and not just the surface finish
is important to reflectivity and absorbtion.

Latex isn't inherently glossy. I suppose some resin
particles (such as one or more acrylics) might be added in
collodial suspension to "water-base" gloss paints to give a
gloss surface and the resin pariticles absorb more light
or, like transparent finishes like polyurethane 
"varnishes" the diff between gloss and flat is that the
flat has microscopic silicate particles added (which is the
only reason you have to stir it btw) that diffuse the light
before it bounces back. But those particles, despite
diffusing light, might reflect more than would otherwise
occur.

Aluminum is great if you can get a really high polish, but
there's no way to keep that polish on the surface unless
you coat the aluminum with something that resists water
vapor penetration and doesn't absorb much visible light.
That turns out to be a pretty neat trick to pull off.

Put flat black paint on aluminum and it acts as a better
heat sink than with glossy black paint or no paint. Why
should that be? Paint and photons can have some pretty
interesting interactions.


sh
--- Derek Parr <derekparr at earthlink_net> wrote:

> Flat white?   would that reflect more than gloss white?
> why would that be?
> 
> curious,
>      -derek

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