A new approach to incandescent bulbs promises to beat LEDs for efficiency. Ognen Ilic and colleagues at MIT replaced the traditional light-bulb filament with a flat tungsten ribbon. They then coated glass sheets with a photonic crystal made of alternating layers of tantalum oxide and silicon dioxide, with thicknesses determined by computer modelling, and sandwiched the tungsten between the two.

The photonic crystals are transparent to visible light but reflect infrared photons back onto the filament so that they reheat it instead of being radiated. The efficiency so far is 6.6%, triple that of conventional light bulbs, but 40% may be reachable, which would far outstrip compact fluorescent bulbs (7% to 13%) and LED’s (5% to 15%).