[TowerTalk] remote tuner enclosure

[Jim Lux]

On 2/20/15 4:19 PM, SPENCER wrote:
> What type of material and/or what color paint should I use to reduce
> heating from the sun
> on my outdoor electronics?
>

white paint.

counter-intuitively
Shiny metal actually gets hotter in the sun than white or black paint. 
That's because the metal has low emissivity, so even though the 
absorption is low, it has even lower emission, so it doesn't radiate the 
heat away as well.  (this is why the seatbelt buckle, the chrome on your 
car or a polished metal railing gets so hot in the sun)

polished metal is down in the 0.02-0.04 range (oxidized silver is 0.04)
paint is about 0.9, as are most substances (your IR thermometer probably 
assumes e=0.9)

aluminum foil, for instance, reflects about 85% of the incident solar 
radiation, so it absorbs 15%.  But because it's emissivity is so low, it 
doesn't radiate heat very well.. it gets hot in the sun.

White paint has an absorbtion around 75-85%, but has emissivity of 0.9. 
  So while it absorbs a bit more than shiny metal, it easily radiates it 
away.


It's called the A/E ratio...

http://contrails.iit.edu/DigitalCollection/1960/WADDTR60-773article08.pdf


The sort of dull aluminum paint might be OK, but I don't have any test data.