LED Lighting:
LED – Light Emitting Diode
A light-emitting-diode lamp is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light.
"LED lamps" may in general refer to conventional semiconductor light-emitting diodes, to organic LEDs (OLED), or polymer light-emitting diodes (PLED) devices, although OLED and PLED technologies are not commercially available in 2010.
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As the light output of individual light-emitting diodes is minute compared to incandescent and compact fluorescent lamps, multiple diodes are often used together. As diode technology has improved, high power light-emitting diodes with higher lumen output are making it possible to replace other lamps with LED lamps. Some high power LED chips used in commercial LED lights can emit 7500 lumens while using only 100 watts. LED lamps can now also be made 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.
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LEDs are damaged by being run at high temperatures, so LED lamps include heat supervision 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.
General purpose lighting needs white light. LEDs emit light in a very small band of wavelengths, emitting strongly colored light. To emit white light from LEDs requires either mixing light from red, green, and blue LEDs, or using a phosphor to convert some of the light to other colors.
The first method (RGB-LEDs) uses multiple LED chips each emitting a different wavelength in close proximity to form a broad white light spectrum. The advantage of this method is that the intensity of each LED can be adjusted to modify the character of the light emitted. The only main disadvantage is high production cost. |
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The second method, phosphor converted LEDs (pcLEDs) uses one short wavelength LED (usually blue or ultraviolet) in combination with a phosphor, which absorbs a portion of the blue light and emits a broader spectrum of white light. The major advantage here is the low production cost, and high colour rendering, while the disadvantage is the inability to vigorously change the character of the light and the fact that phosphor conversion diminishes the efficiency of the device. The low cost and adequate performance makes it the most widely used technology for general lighting today. |
A single LED is a low-voltage solid state device and cannot be directly operated on standard AC current without some circuitry to control the voltage applied and the current flow through the lamp. A series diode and resistor could be used to control the voltage polarity and to limit the current, but this is inefficient since most of the applied voltage would be dropped as wasted heat in the resistor. A single series string of LEDs would minimize dropped-voltage losses, but one LED failure could extinguish the whole string. Paralleled strings increase reliability by providing redundancy. In practice, three strings or more are usually used. To be useful for illumination for home or work spaces, a number of LEDs must be placed close together in a lamp to combine their illuminating effects.
| Further, degradation of different LEDs at various times in a colour-mixed lamp can lead to an irregular colour output. LED lamps usually consist of clusters of LEDs in a housing with both driver electronics, a heat sink and optics. This is required because individual LEDs emit only a fraction of the light of traditional light sources. When using the color-mixing method, a uniform color distribution can be difficult to achieve, while the arrangement of white LEDs is not critical for color balance. |
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LED lamps intended to be interchangeable with incandescent lamps are made in standard lamp (or bulb) shapes, such as an Edison screw base, an MR16 shape with a bi-pin base, or a GU10 (bayonet socket). LED lamps are made in low voltage (typically 12 V halogen-like) varieties, and as replacements for regular AC (e.g. 230 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.
LED Lamps
Many LED lamps have become available as replacements for screw-in incandescent or compact fluorescent light bulbs, ranging from low-power 5–40 watt incandescent bulbs, through conventional replacement bulbs for 60 watt incandescent bulbs (typically requiring about 7 watts of power), and as of 2010 a few lamps were available to replace higher wattage bulbs, e.g., a 13-watt LED bulb which is about as bright as a 100W incandescent.
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A standard general purpose incandescent bulb emits light at an efficiency of about 14 to 17 lumens/W depending on its size and voltage. According to the European Union standard, an energy-efficient bulb that claims to be the equivalent of a 60W tungsten bulb must have a minimum light output of 806 lumens.
Philips makes a number of LED lamps which are commercially available and come with a six year warranty, and a number of smaller producers can be found that sell LED lights that are screw-in replacements for conventional lamps. |
The only LED’s that are truly in their infancy, to such a degree that their viability is questionable, are fluorescent LED replacements. Not only is the retro fit more complicated, but the light output is compromised by the fact that the lamps cannot yet reflect as efficiently as a fully tubular fluorescent fitting.
All in all, LED is the future of lighting, and by 2020 far more lights will be LED based than conventional in the commercial sector....... |
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