A team of chemists at University College London (UCL) have reported in the Journal of Materials Chemistry that they have developed a window coating that, when applied to glass used in buildings or cars, reflects the sun's heat while still letting light in.

While conventional tints block both heat and light, the new coating allows visible wavelengths of light through at all times, but reflects the infrared light that causes heating when temperatures rise above 84 degrees Fahrenheit.

"Technological innovations such as intelligent window coating really open the door to more creative design," said professor Ivan Parkin of UCL's Department of Chemistry, senior author of the paper. "The current trend toward using glass extensively in building poses a dilemma for architects. Do they tint the glass, which reduces the benefit of natural light, or face hefty air conditioning bills?"

The new coating is made from a derivative of vanadium dioxide, which has long been recognized for its heat-reflective properties because of its ability to alternate between acting as a metal and a semiconductor. The difficulty in reducing the switching temperature had been a stumbling block up to this point.

"It's not much good if the material starts to reflect infrared light at 160 degrees Fahrenheit," said Parkin. "We've shown it's possible to reduce the switching temperature to just above room temperature and manufacture it in a commercially viable way."

Researchers are currently looking at such issues as cost to produce, durability and color as the next step in getting the coating to market.