Around for 4 decades, the light-emitting diode (LED) is a popular electronic component. Through the 1970s, red and infrared LEDs were the only kinds commercially available. They found uses as power indicators and numbers for clocks and other equipment. Yellow, green and blue LEDs followed, expanding their uses to include decorative lighting. High-brightness LEDs are now being used for home lighting, though high costs limit customer demand.

LED Defined

1. An LED is a solid-state electronic device related to the diode and transistor. In a circuit, it functions as a regular diode would, but it creates light with little heat. LEDs are packaged in a clear plastic block or capsule. Unlike traditional light bulbs, no glass or vacuum is needed.

   Colored LEDs

2. The light from an LED comes from a connection between layers of different semiconductors. Electricity excites the material to a particular energy state, where it gives off light. Since the energy of the light is nearly the same, the light's color falls in a narrow range of the light spectrum. Common LED colors are red, yellow, green and blue.

   How LEDs Make White Light

3. Most LEDs have a narrow light spectrum, giving them a single color. White LEDs were developed soon after the blue version made its appearance. Early white LEDs were made from separate blue and green parts placed close together in the lamp. Recent white LEDs use a bright blue LED to stimulate a phosphor coating that gives off white light.

   LEDs and Heat

4. LEDs used for power indicators, clock numerals, and the like, run on low voltage and current, creating light with little heat. High-brightness LED lights, however, consume more current and can get warm. For a similar brightness, an LED lamp will be much cooler than an incandescent.

   LED Advantages

5. Incandescent and fluorescent lamps have fragile glass envelopes; LEDs are made of tough plastic. LEDs are more efficient than the other two types of lighting, giving more light per watt of electricity. Fluorescent lamps contain mercury vapor; LEDs are safe to use and dispose. Incandescent and fluorescent lamps have shorter lifetimes and performance limitations in extreme temperatures; LEDs are relatively unaffected by heat and cold.

   Expense

6. As of 2009, LED-based lamps used for room lighting are more expensive than other kinds. LED lamps are not yet mass-manufactured in the quantities that the other types are, keeping prices up. Also, LEDs do not run directly from 110V household AC current; they need 1.5 to 3 volts, requiring a step-down transformer and other parts to work. This also adds expense.

   Duration

7. Since they are semiconductor devices that run cool, they last a long time. Most LEDs are rated at 100,000 hours or about 10 years of continuous operation. They dim slowly with time.