Stay Cool with Paint, Part I

Using paint to keep your home cool and cut energy costs is all about reflection.

You may remember from school that light contains all the colours there are. Objects absorb some of the colours and then reflect others. Black absorbs all the colours and shows none. This is why black objects look black rather than showing our eyes another colour, and it's also why dark things get hotter in the sun and stay hotter longer.

White objects reflect all the colours, showing us just white. Since they don't absorb the light, they also don't absorb heat. That means that white objects stay cooler than black ones. If you put a sheet of black paper and a sheet of white paper in the sun for an hour, you'll find that the whiter paper feels much cooler than the black paper. Put an ice cube on each and you can see the difference.

This is a continuum, of course. Darker colours reflect less light than paler shades. The difference between sky blue and lemon yellow isn't as great as the difference between black and white, but there is a bit of a difference if we had precise tools to measure that difference. The difference between pale blue and deep blue is easier to identify. So even though blue is a cool colour in colour theory and yellow is a warm one, midnight blue will absorb more heat than pale butter yellow, and it will be hotter to the touch in sun.

This is why painting your home in a light colour will make it cooler than painting it in a dark colour. Your roof and your walls should be lighter to keep your energy costs down in the summer. It's not a myth.