Glass that blocks out heat but not light when a room starts getting excessively warm has been developed by UK scientists.

At most room temperatures the glass lets both visible and infrared light pass through. But above 29°C, a substance coating the glass undergoes a chemical change causing it to block infrared light. This will prevent room from overheating in bright sunshine or if temperatures outside start to soar.

Other solutions, such as tinted glass, do not respond to changing conditions. As well as reducing the light entering a room, tinted glass keeps a room cool even when some of the Sun's warmth would be welcome.

The researchers behind the new glass technology believe it could change the way architects design large buildings.

"The current trend towards using glass extensively in building poses a dilemma for architects," says Ivan Parkin, who developed the new glass with colleague Troy Manning at University College London. "Do they tint the glass, which reduces the benefit of natural light or face hefty air conditioning bills?"

Transition temperature

The glass is coated the chemical vanadium dioxide. This material transmits both visible and infrared wavelengths of light, and normally undergoes a change at about 70°C.

Above this transition temperature, the electrons in the material alter their arrangement. This turns it from a semiconductor into a metal, and makes it block infrared light. Parkin and Manning lowered the transition temperature to 29°C by doping the material with the metal tungsten.

They also found a way to incorporate deposition of the coating into a conventional glass manufacturing process. This should make it relatively cheap to mass produce, they claim, with a commercial version of the glass ready within three years.

However, a number of issues still need to be overcome. Firstly, the substance is not permanently fixed to the glass. Also, the coating itself currently has a strong yellow tint.

But Manning believes it should be possible to overcome these issues. "You could add another substance, like titanium dioxide, to fix it to the glass," he told New Scientist. "And you could use a dye that would cancel out the yellow."

Journal reference: Journal of Materials Chemistry DOI: 10.1039/b403576n