Window of opportunity: Shanhui Fan and colleagues

When the weather gets hot, everyone wants to stay cool. That often means turning on the air conditioning, which consumes vast amounts of energy – and money – in developed countries. But that could change, thanks to a new photonic device that can cool to below the ambient temperature while consuming no energy.

Cooling accounts for around 15% of the energy used in buildings in the US and contributes heavily to greenhouse-gas emissions. Worldwide, energy consumption related to cooling is expected to surpass that used for heating by 2070.

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Objects can cool themselves without consuming energy by radiating energy in the form of infrared light. This process is not normally very efficient because objects can also be warmed by convective air currents and by absorbing radiation emitted by other objects and by the air. However, air absorbs and emits very little infrared radiation at wavelengths of around 8–13 μm. It is through this “window” that the Earth lowers its temperature at night – especially when the sky is clear – by sending […]