Why is chrome hot and white not?
In the direct sun, black gets hot to the touch and white not. I understand that the white is reflecting and the black absorbing, but WHY are highly reflective surfaces like chrome or shiny stainless steel hot to the touch? A stainless equipment box in the sun is hot to the touch and hot inside as well. What’s going in? Related question: If the SS box was painted white, would it then be cooler?
UNDERSTANDING EMISSIVITY
Emissivity is the ability for an object to release “emit” radiant heat. The lower the emissivity, the more difficult it is for heat to leave the surface in radiant form. This why chrome tools in your toolbox and car door handles get too hot to touch when exposed to the sun.
Most paints emit in the .90 range which is very high. Chrome has an emissiviy or “E” value of .05. It will take more time for a chrome bumper to get as hot as one painted black but the low emissivity of chrome traps the heat making it much hotter. The low E value of chrome prevents the absorbed heat from escaping making the surface hot. This is why black chrome solar panels provide hotter water than panels painted flat black. Black chrome will take a little longer to get hot, but once it does, the low E selective surface traps heat in the absorber which in turn transfers it through conduction into the water passages.
I think the answer to the question of painting the stainless steel box white will make it cooler is no. Painting it white will probably just change the rate at which the box absorbs heat, but in the end it will heat to the same temp.
