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Essay on LED Lamps
- Essay on the Introduction to LED Lamp
- Essay on Light Technology used in LED Lamps
- Essay on Lamp Sizes and Bases
- Essay on Light Bulbs used in LED Lamps
- Essay on the Applications of LED Lamps
Essay # 1. Introduction to LED Lamp:
A light-emitting-diode lamp is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light. The term ‘LED light bulb’ is also colloquially used. ‘LED lamp’ may in general refer to conventional semiconductor light- emitting diodes, to organic LEDs (OLED), or polymer light-emitting diodes (PLED) devices.
Since the light output of individual light-emitting diodes is small compared to incandescent and compact fluorescent lamps, multiple diodes are often used together. In recent years, 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.
One high power LED chip used in some commercial LED lights can emit 7527 lumens while using only 100 watts. LED lamps can 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. 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.
An assortment of LED light bulbs that are commercially available as of 2010 as replacements for screw-in bulbs, including floodlight fixtures (left), reading light (center), household lamps (center right and bottom), and low-power accent light (right) applications.
Essay # 2. Light Technology used in LED Lamps:
General purpose lighting needs white light. LEDs emit light in a very small band of wavelengths, emitting strongly colored light. The color is characteristic of the energy band gap of the semiconductor material used to make the LED. 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 the broad white light spectrum. The advantage of this method is that the intensity of each LED can be adjusted to ‘tune’ the character of the light emitted. The major disadvantage is high production cost.
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 mechanism is similar to the way a fluorescent lamp emits white light from a UV-illuminated phosphor.)
The major advantage here is the low production cost, and high CRI (color rendering index), while the disadvantage is the inability to dynamically change the character of the light and the fact that phosphor conversion reduces 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.
This is 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.
Further, degradation of different LEDs at various times in a color-mixed lamp can lead to an uneven color output. LED lamps usually consist of clusters of LEDs in a housing with both driver electronics, a heat sink and optics.
Essay # 3. 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.
Essay # 4. Light Bulbs used in 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.
The technology is improving rapidly, and new energy-efficient consumer LED lamps have been announced by big companies in lighting industry such as Osram Sylvania, Philips, and General Electric etc.
White LED lamps have achieved market dominance in applications where high efficiency is important at low power levels. Some of these applications include flashlights, solar-powered garden or walkway lights, and bicycle lights. Monochromatic (colored) LED lamps are now commercially used for traffic signal lamps, where the ability to emit bright monochromatic light is a desired feature, and in strings of holiday lights.
Essay # 5. Applications of LED Lamps:
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.
Compared to fluorescent bulbs, advantages claimed for LED light bulbs are that they contain no mercury (unlike compact fluorescent light bulbs), that they turn on instantly, and that lifetime is unaffected by cycling on and off, so that they are well suited for light fixtures where bulbs are often turned on and off. LED light bulbs are also less apt to break.
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. Due to 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. In contrast to other lighting technologies, LED emission tends to be directional (or at least lambertian). This can be either an advantage or a disadvantage, depending on the requirements of the application.
For applications where non-directional light is required, either a diffuser is used, or multiple individual LED emitters are used to cover different directions.