LED lamps (LED light bulbs) are solid-state lamps that use light-emitting diodes (LEDs) as the source of light. The current commercially available LED Lamps are conventional semiconductor light-emitting diodes. Recent technological advances in high power light-emitting diodes with higher lumen output are making it possible to replace incandescent and compact fluorescent lamps with LED lamps. One high power LED chip can emit 7,527 lumens while using only 100 watts. LED lamps are interchangeable with other types of lamps.
Diodes use direct current (DC) electrical power, so LED lamps must also include internal circuits to operate from standard AC voltage. LEDs are damaged by being run at higher temperatures, so LED lamps typically include heat management elements such as heat sinks and cooling fins. LED lamps offer long service life and high energy efficiency, but initial costs are higher than those of fluorescent lamps.
LEDs emit light in a very small band of wavelengths, emitting strongly colored light. To emit white light from LEDs requires mixing light from red, green, and blue LEDs, or using a phosphor to convert some of the light to other colors. LED lamps are used for both general and special-purpose lighting. Where colored light is needed, LEDs come in multiple colors, which are emitted with no need for filters. This improves the energy efficiency over a white light source that generates all colors of light then discards some of the visible energy in a filter.
White-light light-emitting diode lamps have the traits of long life expectancy and relatively low energy use. The LED sources are compact, which gives flexibility in designing lighting fixtures and good control over the distribution of light with small reflectors or lenses. Because of the small size of LEDs, control of the spatial distribution of illumination is extremely flexible, and the light output and spatial distribution of a LED array can be controlled with no efficiency loss. LED lamps have no glass tubes to break, and their internal parts are rigidly supported, making them resistant to vibration and impact. With proper driver electronics design, an LED lamp can be made dimmable over a wide range; there is no minimum current needed to sustain lamp operation.
LEDs using the color-mixing principle can emit a wide range of colors by changing the proportions of light generated in each primary color. This allows full color mixing in lamps with LEDs of different colors.
Lamp Sizes and Bases
LED lamps intended to be interchangeable with incandescent lamps are made in standard light bulb shapes, such as an Edison screw base, an MR16 shape with a bi-pin base, or a GU5.3 (Bipin cap) or GU10 (bayonet socket). LED lamps are made in low voltage (typically 12 V halogen-like) varieties, and as replacements for regular AC (e.g. 120 or 240 V AC) lighting. These lamps typically include circuitry to rectify the AC power and to convert the voltage to a level usable by the internal LED elements.
Comparison to other Lighting Technologies
Compared to fluorescent bulbs, LED light bulbs they contain no mercury, they turn on instantly, less apt to break, and lifetime use is unaffected by cycling on and off. This makes LED lamps well suited for light fixtures where bulbs are often turned on and off. Incandescent lamps Incandescent lamps generate light by passing electric current through a resistive filament, thereby heating the filament to a very high temperature so that it glows and emits visible light. Incandescent light is highly inefficient, as about 98% of the energy input is emitted as heat. A 100 W light bulb emits about 1,700 lumens, about 17 lumens/W. Incandescent lamps are relatively inexpensive to make. The typical lifespan of an AC incandescent lamp is around 1,000 hours.
Fluorescent lamps work by passing electricity through mercury vapor, which in turn emits ultraviolet light. The ultraviolet light is then absorbed by a phosphor coating inside the lamp, causing it to glow, or fluoresce. While the heat generated by a fluorescent lamp is much less than its incandescent counterpart, energy is still lost in generating the ultraviolet light and converting this light into visible light. If the lamp breaks, exposure to mercury can occur. Linear fluorescent lamps are typically five to six times the cost of equivalent incandescent lamps but have life spans around 10,000 and 20,000 hours. Lifetime varies from 1,200 hours to 20,000 hours for compact fluorescent lamps. The life expectancy depends on the number of on/off cycles, and is lower if the light is cycled often. The efficiency of fluorescent tubes with modern electronic ballasts and compact fluorescents commonly ranges from 50 to 67 lumens/W.