Liquid-cooled LED bulb. LED light bulbs are solid-state lamps that use light-emitting diodes (LEDs), as opposed to the tungsten filament of an incandescent light bulb. They last for longer and are more efficient, but are degraded by high temperatures. The use of liquid cooling systems, as here, makes use of LED bulbs more feasible, with a range of commercial applications appearing from 2009. Photographed in September 2010.