Briefs: Chameleon tiles for energy savings

It is a well-known fact that dark surfaces absorb the sun's heat, whereas white surfaces reflect it. US Secretary of Energy, Steven Chu, considers that turning all roofs white would eliminate as much greenhouse gas emissions in 20 years as the whole world produces in a year. A team of recent Massachusets Institute of Technology (MTI) graduates has pushed this logic further by developing roof tiles that change colour according to the temperature. The team's lab measurements show that in their white state the tiles reflect about 80% of the sunlight falling on them, while when in black they reflect only about 30%. This implies that in their white state, they could save as much as 20% of present cooling costs. Heat savings from the black state in lower temperatures have not yet been quantified.