What is LED Lighting

The LED or the light emitting diode is a light source that is based on the semiconductor diode. The technology for LEDs has been around since 1962 and was originally used as light indicators for devices. When LED technology was further explored, its potential for being the future for sustainable and efficient lighting was discovered.

Over the years, LEDs have become more sophisticated and enhanced with advanced engineering to expand possible uses beyond simple light indicators. The small size of LED lights encourages a variety of design options. They are now being used for space lighting in a wide variety of settings, including industrial and residential lighting. LEDs incorporate an impressive combination of beneficial characteristics such as being impressively durable and fit for rugged use, and are also the choice solution for green lighting because of their energy efficiency.

The LED has also become the leading choice for sustainable (or green) and efficient lighting. It outperforms both incandescent and fluorescent lighting solutions by emitting as much as 80% of the electric energy it consumes as light energy, with only 20% being given off as heat. It is also the most energy efficient, and therefore the most cost effective, lighting solution today.

The U.S. Department of Energy and its partners are working to accelerate advances in solidstate lighting – a pivotal emerging technology that promises to fundamentally alter lighting in the future.

“No other lighting technology offers as much potential to save energy and enhance the quality of our building environments, contributing to our nation’s energy and climate change solutions.”

How LEDs Work

LEDs differ from traditional light sources in the way they produce light. In an incandescent lamp, a tungsten filament is heated by electric current until it glows or emits light. In a fluorescent lamp, an electric arc excites mercury atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light.

An LED, in contrast, is a semiconductor diode. It consists of a chip of semiconducting material treated to create a structure called a p-n (positive-negative) junction. When connected to a power source, current flows from the p-side or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers (electrons and electron holes) flow into the junction from electrodes. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon (light).

LED TYPES

Low power LEDs commonly come in 5 mm size, although they are also available in 3 mm and 8 mm sizes. These are fractional wattage devices, typically 0.1 watt, operate at low current (~20 milliamps) and low voltage (3.2 volts DC), and produce a small amount of light, perhaps 2 to 4 lumens.

High power LEDs come in 1-3 watt packages. They are driven at much higher current, typically 350, 700, or 1000 mA, and—with current technology—can produce 40-80 lumens per 1-watt                     

XX LEDs come in many different shapes and sizes. Some current products from the leading LED manufacturers are shown below.

Comparing LEDs to Traditional Light Sources

Energy efficiency proponents are accustomed to comparing light sources on the basis of luminous efficacy. To compare LED sources to CFLs, for example, the most basic analysis should compare lamp-ballast efficacy to LED+driver efficacy in lumens per watt. Data sheets for white LEDs from the leading manufacturers will generally provide “typical” luminous flux in lumens, test current (mA), forward voltage (V), and junction temperature (T_j), usually 25 degrees Celsius.

Due to the directional nature of their light emission, LEDs potentially have higher application efficiency than other light sources in certain lighting applications. Fluorescent and standard “bulb” shaped incandescent lamps emit light in all directions. Much of the light produced by the lamp is lost within the fixture, reabsorbed by the lamp, or escapes from the fixture in a direction that is not useful for the intended application. For many fixture types, including recessed downlights, troffers, and under-cabinet fixtures, it is not uncommon for 40-50% of the total light output of the lamp(s) to be lost before it exits the fixture.