An upcoming project has an enclosure for electronics that is exposed to sunlight. I wanted to see if silver or white color paint was better at reducing the solar heating in the enclosure. I picked 5 different spray paints to test along with flat black as a sort of control.
- Rust-Oleum flat black enamel (control)
- Rust-Oleum Mirror Effect
- Krylon Rust Tuff White
- Rust-Oleum Silver Chrome
- Krylon interior exterior white
- Rust-Oleum Pure White Enamel
To test the paints I painted cardboard 6″X6″ squares with each paint and stapled the squares to a piece of scrap wood to support them and set the samples out in the noon sun.
I tried measuring the painted surface of each square with an IR thermometer but the emissivity of the mirror effect paint was way different than the others throwing the measurements off. So I measured the back side of each square, since that was plain cardboard. Below are the resulting temperature measurements.
As expected the black paint had the highest temperature. The mirror effect paint had the lowest temperature. Interestingly the silver chrome was worse that the white paints. This tells me that the type of silver paint is important. Of the white paints the Rust-Oleum Pure White Enamel had the lowest temperature.
There are some other considerations with the mirror effect paint. It is intended to be used to make a mirror by spraying it on the back of glass or other clear material. It is also not rated for outdoor used. The enclosure to be painted is made of clear plexiglass where the mirror effect paint on the inside would be more mirror like than on the cardboard. So it would actually be indoors and possibly more reflective than on the cardboard.
Most things you see that are painted to reduce solar heating are painted white so I am inclined to use the Rust-Oleum Pure White Enamel but the mirror effect paint deserves some more experimentation. Now to figure out how to compare it with white when painted on the inside of an enclosure.