Saturday, 26 March 2011

Applications of led light

LED uses fall into four major categories:

    * Led outdoor signs where light goes more or less directly from the source to the human eye, to convey a message or meaning.
    * Indoor and outdoor illumination where light is reflected from objects to give visual response of these objects.
    * Measuring and interacting with processes involving no human vision.
    * Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light.

For more than 70 years, until the LED, practically all lighting was incandescent and fluorescent with the first fluorescent light only being commercially available after the 1939 World's Fair.

 Led outdoor signs

The low energy consumption, low maintenance and small size of modern LEDs has led to uses as status of led outdoor signs on a variety of equipment and installations. Large-area LED outdoor signs are used as stadium displays and as dynamic decorative displays. Thin, lightweight message displays are used at airports and railway stations, and as destination displays for trains, buses, trams, and ferries.

One-color light is well suited for traffic lights and signals, exit signs, emergency vehicle lighting, ships' navigation lights or lanterns (chromacity and luminance standards being set under the Convention on the International Regulations for Preventing Collisions at Sea 1972, Annex I and the CIE) and LED-based Christmas lights. In cold climates, LED traffic lights may remain snow covered. Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, e.g. night time animal watching and military field use.

Because of their long life and speedy changing times, LEDs have been used in brake lights for cars high-mounted brake lights(new BMW and Audi), trucks, and buses, and in turn signals for some time, but lots of vehicles now use LEDs for their rear light clusters. The use in brakes improves safety, due to a great reduction in the time needed to light fully, or faster rise time, up to 0.5 second faster than an incandescent bulb. This gives drivers behind more time to react. It is reported that at normal highway speeds, this equals one automobile length equivalent in increased time to react. In a dual intensity circuit (i.e., rear markers and brakes) if the LEDs are not pulsed at a speedy frequency, they can generate a phantom array, where ghost images of the LED will appear if the eyes quickly scan across the array. White LED headlamps are beginning to be used. Using LEDs has styling advantages because LEDs can form much thinner lights than incandescent lamps with parabolic reflectors.

Due to the relative cheapness of low output LEDs, they are also used in lots of temporary makes use of such as throwies, glowsticks, and the photonic textile Lumalive. Artists have also used LEDs for LED art.

Weather/all-hazards radio receivers with Specific Area Message Encoding (SAME) have four LEDs: red for warnings, orange for watches, and yellow for advisories & statements whenever issued.


LED street lights are employed on poles & in parking garages. In 2007, the Italian village Torraca was the first place to convert its whole illumination process to LEDs.

With the development of high efficiency & high power LEDs it's grown feasible to make use of LEDs in lighting & illumination. Replacement light bulbs have been made, as well as dedicated fixtures & LED lamps. LEDs are used as street lights & in other architectural lighting where color changing is used. The mechanical robustness & long lifetime is used in automotive lighting on cars, motorcycles & on bicycle lights.

LEDs are also suitable for backlighting for LCD televisions & lightweight laptop computer displays & light source for DLP projectors. RGB LEDs raise the color gamut by as much as 45%. Screens for TV & computer displays can be made thinner using LEDs for backlighting.

LEDs are used in aviation lighting. Airbus has used LED lighting in their Airbus A320 Enhanced since 2007, & Boeing designs its use in the 787. LEDs are also being used now in airport & heliport lighting. LED airport fixtures currently include medium-intensity runway lights, runway centerline lights, taxiway centerline & edge lights, guidance signs & obstruction lighting.

The dearth of IR/heat radiation makes LEDs ideal for stage lights using banks of RGB LEDs that can basically change color & decrease heating from traditional stage lighting, as well as medical lighting where IR-radiation can be harmful.

LEDs are used increasingly often in aquarium lights. for reef aquariums, LED lights provide an efficient light source with less heat output to help maintain optimal aquarium temperatures. LED-based aquarium fixtures also have the advantage of being by hand adjustable to emit a specific color-spectrum for ideal coloration of corals, fish, & invertebrates while optimizing photosynthetically active radiation (PAR) which raises growth & sustainability of photosynthetic life such as corals, anemones, clams, & macroalgae. These fixtures can be electronically programmed to simulate various lighting conditions throughout the day, reflecting phases of the sun & moon for a dynamic reef experience. LED fixtures usually cost up to four times as much as similarly rated fluorescent or high-intensity discharge lighting designed for reef aquariums & are not as high output to date.

LEDs are small, long lasting & require small power, so they are used in hand held devices such as flashlights. LED strobe lights or camera flashes operate at a safe, low voltage, in lieu of the 250+ volts often present in xenon flashlamp-based lighting. This is useful in cameras on mobile rings, where space is at a premium & bulky voltage-raising circuitry is undesirable. LEDs are used for infrared illumination in night vision makes use of including security cameras. A ring of LEDs around a video camera, aimed forward in to a retroreflective background, allows chroma keying in video productions.

LEDs are used for decorative lighting as well. Makes use of include but are not limited to indoor/outdoor decor, limousines, cargo trailers, conversion vans, cruise ships, RVs, boats, automobiles, & utility trucks. Decorative LED lighting can also come in the kind of lighted company signage & step & aisle lighting in theaters & auditoriums.
Smart lighting

Light can be used to get broadband data, which is already implemented in IrDA standards using infrared LEDs. Because LEDs can cycle on and off millions of times per second, they can be wireless transmitters and access points for data transport. Lasers can also be modulated in this manner.

Sustainable lighting
Efficient lighting is needed for sustainable architecture. A 13 watt LED lamp emits 450 to 650 lumens. which is equivalent to a standard 40 watt incandescent bulb. A standard 40 W incandescent bulb has a lifespan of 1,000 hours while an LED can continue to operate with reduced efficiency for more than 50,000 hours, 50 times longer than the incandescent bulb.

 Energy consumption

One kilowatt-hour of electricity will cause 1.34 pounds (610 g) of CO2 emission. Saying that the average light bulb is on for 10 hours a day, one 40-watt incandescent bulb will cause 196 pounds (89 kg) of CO2 emission per year. The 13-watt LED equivalent will only cause 63 pounds (29 kg) of CO2 over the same time span. A building’s carbon footprint from lighting can be reduced by 68% by exchanging all incandescent bulbs for new LEDs in warm climates. In cold climates, the energy saving may be lower, since more heating is needed to compensate for the lower temperature.

 Economically sustainable

LED light bulbs could be a cost-effective option for lighting a home or office space because of their very long lifetimes. Consumer use of LEDs as a replacement for conventional lighting system is currently hampered by the high cost and low efficiency of available products. 2009 DOE testing results showed an average efficacy of 35 lm/W, below that of typical CFLs, and as low as 9 lm/W, worse than standard incandescents. The high initial cost of the commercial LED bulb is due to the expensive sapphire substrate which is key to the production process. The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted.

 Non-visual applications

The light from LED's can be modulated quickly so they are used extensively in optical fiber and Free Space Optics communications. This include remote controls, such as for TVs and VCRs, where infrared LEDs are often used. Optoisolators use an LED combined with a photodiode or phototransistor to provide a signal path with electrical isolation between five circuits. This is useful in medical equipment where the signals from a low-voltage sensor circuit (usually battery powered) in contact with a living organism must be electrically isolated from any feasible electrical failure in a recording or monitoring tool operating at potentially risky voltages. An optoisolator also allows information to be transferred between circuits not sharing a common ground potential.

Plenty of sensor systems depend on light as the signal source. LEDs are often ideal as a light source due to the requirements of the sensors. LEDs are used as movement sensors, for example in optical computer mice. The Nintendo Wii's sensor bar makes use of infrared LEDs. In pulse oximeters for measuring oxygen saturation. Some flatbed scanners use arrays of RGB LEDs than the typical cold-cathode fluorescent lamp as the light source. Having independent control of four illuminated colors allows the scanner to calibrate itself for more correct color balance, and there is no need for warm-up. Further, its sensors only need be monochromatic, since at any one time the page being scanned is only lit by one color of light. Touch sensing: Since LEDs may even be used as photodiodes, they can be used for both photograph emission and detection. This might be used in for example a touch-sensing screen that register reflected light from a finger or stylus.

Plant growers have an interest in LEDs because they are more energy efficient, emit less heat (can destroy plants close to hot lamps), and can provide the optimum light frequency for plant growth and bloom periods compared to currently used grow lights: HPS (high pressure sodium), MH (metal halide) or CFL/low-energy. However, LEDs have not replaced these grow lights due to higher cost. As mass production and LED kits create, the LED products will become cheaper.

Plenty of materials and biological systems are sensitive to, or dependent on light. Grow lights use LEDs to increase photosynthesis in plants and bacteria and viruses can be removed from water and other substances using UV LEDs for sterilization. Other makes use of are as UV curing devices for some ink and coating methods, and in LED printers.

LEDs have also been used as a medium quality voltage reference in electronic circuits. The forward voltage drop can be used in lieu of a Zener diode in low-voltage regulators. Red LEDs have the flattest I/V curve above the knee. Nitride-based LEDs have a steep I/V curve and are useless for this purpose. Although LED forward voltage is far more current-dependent than a lovely Zener, Zener diodes are not widely obtainable below voltages of about 3 V.
 Light sources for machine vision systems

Machine vision systems often need bright and homogeneous illumination, so features of interest are simpler to process. LEDs are often used for this purpose, and this is likely to stay one of their major makes use of until cost drops low to make signaling and illumination makes use of more widespread. Barcode scanners are the most common example of machine vision, and plenty of low cost ones use red LEDs in lieu of lasers. Optical computer mice are also another example of LEDs in machine vision, as it is used to provide an even light source on the surface for the miniature camera within the mouse. LEDs constitute an  ideal light source for machine vision systems for several reasons:

The size of the illuminated field is usually comparatively small and machine vision systems are often expensive, so the cost of the light source is usually a minor concern. However, it might not be simple to replace a broken light source placed within complex machinery, and here the long service life of LEDs is a benefit.

LEDs can be basically strobed (in the microsecond range and below) and synchronized with imaging. High-power LEDs are available allowing well lit images even with short light pulses. This is often used to receive crisp and sharp still images of quickly moving parts.

LED elements tend to be small and can be placed with high density over flat or even-shaped substrates (PCBs etc.) so that bright and homogeneous sources can be designed which direct light from tightly controlled directions on inspected parts. This can often be obtained with small, low-cost lenses and diffusers, helping to accomplish high light densities with control over lighting levels and homogeneity. LED sources can be formed in several configurations (spotlights for reflective illumination; ring lights for coaxial illumination; back lights for contour illumination; linear assemblies; flat, large format panels; dome sources for diffused, omnidirectional illumination).

LEDs come in several different colors and wavelengths, allowing simple use of the best color for each need, where different color may provide better visibility of features of interest. Having a exactly known spectrum allows tightly matched filters to be used to separate informative bandwidth or to reduce disturbing effects of ambient light. LEDs usually operate at comparatively low working temperatures, simplifying heat management and dissipation. This enables using plastic lenses, filters, and diffusers. Waterproof units can also basically be designed, allowing use in harsh or wet environments (food, beverage, oil industries).

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