LED lightbulbs are solid-state lamps that use light-emitting diodes (LEDs) to produce light. The bulbs are made of semiconductor light-emitting diodes, which use direct current electrical power, so LED bulbs must also include internal circuits to operate using the standard AC current found in homes. The United States Department of Energy has partnered with big-box retailers and manufacturers to help shoppers get information that allows them to make decisions regarding this type of lighting technology.
LED bulbs are designed to last up to 10 times longer than compact fluorescent lightbulbs (CFLs); some manufacturers advertise a lifespan of up to 60,000 hours, and the lighting levels remain constant throughout the life of the bulb. The light they produce comes on instantly, unlike CFLs, which need time to warm up and come to full brightness. They are also resistant to damage from the average bump.
Unlike CFLs, LED bulbs contain no mercury. They operate at cooler temperatures than incandescent bulbs and CFLs. Incandescent bulbs in particular can generate substantial amounts of heat, which in turn increases the need for air conditioning. LED bulbs also use far less electricity compared to CFLs and incandescent lights of the same wattage.
The lighting from LED bulbs is directional, meaning that they do not radiate light from all angles; light emanates from the top half of the bulb, providing less ambient light from a single bulb. This makes them less than ideal for applications other than track or canned lighting where directional light is desired.
LED bulbs are expensive, costing anywhere from $20 to $120 per unit, depending on the company and product. This can be a deterring factor when the lower lighting levels each bulb produces is taken into account, since more bulbs might be required to obtain the desired light output.