What are LEDs?
LED is the acronym for Light-Emitting Diode. A diode is an electronic semi-conductor component that allows an electric current to flow in one direction and blocks current flow in the opposite direction. An LED is a diode consisting of a semi-conductor chip constructed in a way that generates photons to emit energy in the form of light when an electric current passes through it.
Compared to conventional light sources that first convert electrical energy into heat, and then into light, LEDs convert electrical energy directly into light, delivering efficient light generation with little-wasted electricity.
Benefits of LED lighting
Energy Efficiency : LED lighting generally consumes about 20% of the power used by incandescent and halogen lamps, making LED technology 5 times more energy efficient. LEDs are also more efficient than CFLs and rapidly gaining on the efficacy of fluorescent tubes.
Environmentally Friendly : LED lighting is an excellent green technology in that is offers the potential for a dramatic reduction in energy consumption. In addition, LEDs are mercury-free and safe for the environment, unlike fluorescent tubes and CFLs which contain mercury and require special handling and disposal.
Long Life / Low Maintenance
Durable / Robust : Unlike incandescent, halogen, fluorescent, CFL compact fluorescent lamps and other types of lamps, LEDs are solid state devices making them much less fragile and more resistant to damage caused by impact shock or vibration. LED lamps are ideal for use in applications requiring frequent on/off switching whereas other light sources can burn out quickly if switched frequently.
Low Cost of Ownership / Save Money
Light Directed where needed / Light Pollution minimised : LED lighting luminaires are directional, sending light only where it is needed and therefore preventing wasted energy and light pollution. LEDs have a more compact form than other light sources such as CFL and facilitate more efficient optics and better control of light.
Instant ON/OFF : LEDs lamps switch on to emit full light output capacity instantly and do not require a warm up period as in the case of fluorescent and CFL light sources. In addition, LEDs can be switched on and off continuously without reducing their life span.
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).
The specific wavelength or color emitted by the LED depends on the materials used to make the diode. Red LEDs are based on aluminum gallium arsenide (AlGaAs). Blue LEDs are made from indium gallium nitride (InGaN) and green from aluminum gallium phosphide (AlGaP).
"White" light is created by combining the light from red, green, and blue (RGB) LEDs or by coating a blue LED with yellow phosphor.
Glossary of LED terminology
Solid-state lighting (SSL) technology uses semi-conducting materials to convert electricity into light. SSL is an umbrella term encompassing both light-emitting diodes (LEDs) and organic light emitting diodes (OLEDs).
Light-emitting diodes (LEDs) are based on inorganic (non-carbon based) materials. An LED is a semi-conducting device that produces light when an electrical current flows through it. LEDs were first developed in the 1960s but were used only in indicator applications until recently.
General illumination is a term used to distinguish between lighting that illuminates from tasks, spaces, or objects lighting used in indicator or purely decorative applications. In most cases, general illumination is provided by white light sources, including incandescent, fluorescent, high-intensity discharge sources, and white LEDs. Lighting used for indication or decoration is often monochromatic, as in traffic lights, exit signs, vehicle brake lights, signage, and holiday lights.
Luminous efficacy is the most commonly used measure of the energy efficiency of a light source. It is stated in lumens per watt (lm/W), indicating the amount of light a light source produces for each watt of electricity consumed. For white high-brightness LEDs, luminous efficacy published by LED manufacturers typically refers to the LED chip only, and doesn't include driver losses.
Correlated color temperature (CCT) is the measure used to describe the relative color appearance of a white light source. CCT indicates whether a light source appears more yellow/gold/orange or more blue, in terms of the range of available shades of "white." CCT is given in kelvins (unit of absolute temperature).
Color rendering index (CRI) indicates how well a light source renders colours of people and objects, compared to a reference source. See more on CRI.
Phosphor conversion is a method used to generate white light with LEDs. A blue or near-ultraviolet LED is coated with a yellow or multichromatic phosphor, resulting in white light.
OLEDs (Organic Light Emitting Diodes) are based on organic (carbon based) materials. In contrast to LEDs, which are small point sources, OLEDsare made in sheets which provide a diffuse area light source. OLEDtechnology is developing rapidly and is increasingly used in display applications such as cell phones and HD-TVs. OLEDs are emerging as a viable general illumination source as technological advancements are made in light output, colour, efficiency, cost, and lifetime.
RGB is the acronym for Red, Green, and Blue, the three primary colours of light. When the primary colours are mixed, the resulting light appears white to the human eye. Mixing the light from red, green, and blue LEDs is one way to produce white light. An alternative method to generate white light is to coat a blue or near-ultraviolet LED with a yellow or multichromatic phorphor. The term RGB is commonly used to denote a light module or luminaire that has the ability to change colour and may include features such as colour phasing, switching and static colours.
Quick Guide to LED Lighting Specification Terms