What is LED ? What are the advantages?

A light-emitting diode (LED) (pronounced L-E-D) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962,early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor.Following are the major advantages for LED technology:

1. Efficiency: LEDs emit more light per watt than incandescent light bulbs.Their efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes.

2. Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs.

3. Size: LEDs can be very small (smaller than 2 mm²) and are easily populated onto printed circuit boards.
4. On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond. LEDs used in communications devices can have even faster response times.
5. Cycling: LEDs are ideal for uses subject to frequent on-off cycling, unlike fluorescent lamps that fail faster when cycled often, or HID lamps that require a long time before restarting.
6. Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current.
7. Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.
8. Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs.
9. Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000–2,000 hours.
10. Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile.
11. Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.
12. Low toxicity: LEDs do not contain mercury, unlike fluorescent lamps.

What is luminaire & how is it different from light sources?

A light fixture, light fitting, or luminaire is an electrical device used to create artificial light and/or illumination, by use of an electric lamp. All light fixtures have a fixture body, a light socket to hold the lamp and allow for its replacement—which may also have a switch to operate the fixture, and also require an electrical connection to a power source, often by using electrical connectors (e.g. plugs) with portable fixtures. Light fixtures may also have other features, such as reflectors for directing the light, an aperture (with or without a lens), an outer shell or housing for lamp alignment and protection, and an electrical ballast and/or power supply.The use of the word "lamp" to describe light fixtures is common slang for an all-in-one luminary unit, usually portable "fixtures" such as a table lamp or desk lamp (in contrast to a true fixture, which is fixed in place with screws or some other semi-permanent attachment). In technical terminology, a lamp is the light source, what is typically called the light bulb..

What is the need for retroactive designs in some applications?

Specific applications such as Commercial,Retail and Industrial lighting employs sophisticated luminaires or housing fixtures for the Compact Fluorescent Lamp,Fluorescent Tube-light, Metal Halide or High Pressure Sodium Vapor lamps. The inner space usually allows LED lamps to be retrofitted with the only replacement of conventional lighting source and its accessories. The fixtures are mostly spacious with appealing aesthetics and are expensive. The disposal of such costly luminaire also requires certain modifications in existing Infrastructure for new lighting appliances. Hence to prevent the under utilization capacity of the existing resources for lighting and similar issues as mentioned above, Retro-activeness is a must feature for new lighting technology.

Which environmental concerns are addressed by LED technology?

1mg of Mercury(Hg) has the potential to pollute 7 gallons of water. 1kWh of electricity generated at Power Plant emits 610g of CO2 as per the Indian standards. Considering the current transmission and distribution efficiency of the Power players in India, 1kWh saved at the consumption site is equivalent to 2kWh generated at the Power plant. Electricity tariffs are expected to inflate for the next 8 years since the growth in capacity of Power plants is not picking up with the rise in demand for electricity. LEDs unlike CFLs are devoid of Hg or other hazardous ingredients because of which their disposal is not major environmental concern. Again LEDs do not emit UV and IR. They help in saving lighting energy by as much as 80% over traditional lamps. Their carbon footprint being negligible adds GREEN tag to this technology.

What are economics for implementation of this technology?

Usually large scale implementation of LED technology is presently hindered due to the high initial investment which is nearly three to four times than that in traditional lamp sources.The break even for LED lights can be shortened to less than a year if retroactively designed in accordance with the application. The payback period is in the vicinity of two years or less depending upon the nature of target replacement. The savings may be accelerated under KYOTO protocol by trading of the carbon credits gained on implementation of this technology. LED lights are expected to cut down maintenance or replacement costs for 6 continuous years of operation. As per our calculations, Internal Rate of Return for our LED based products is pegged in the vicinity of 30% highest in the industry. Even investments on machines or equipments are not fetching returns within short span of 18 months. Again after break even the technology will be delivering savings for next 54 weeks approximately. Kindly Refer below sample economic considerations pdfs for replacements of Incandescent Bulb/Fluorescent Tubes/Compact Fluorescent Lamp/Metal Halide/High Pressure Sodium Vapor Lamp with LEDs highlighting details of additional investments,payback periods and net savings at the end of 50,000 operating hours(6years) separately for each case.

Where LEDs does possesses lucrative applications?

Places where lighting energy is a significant portion of overall energy consumption, lights are in continuous operation for almost 24 hrs a day and maintenance due to lamp replacement is time consuming or challenging task are some of the most attractive applications of LED based lighting offering promising returns on the initial investments. Naming few of them includes Industrial, Commercial and Roadway lighting applications. Infrastructure operated day and night at full utilization capacity can also yield quick returns within less than 2 years.

What kind of electronic drivers are needed for reliable operation of LEDs?

Due to the steep slope of V-I graph for power LED(s), Constant Current driver is usually preferred since the output luminous intensity of them is proportional to the driving current passing through them. This also ensures reliable and safe operation of LED(s) for long lasting burning. Also the LED driver must be regulating the output current with minimum ripples in the output load. It should absorb spikes in the AC input line and accordingly protect the load from any kind of harms. The drivers are required to be shut down in case of short circuits at the output side so as to prevent the excess current through LED load.The electrolytic capacitor is the present life limiting factor for the drivers to maximum of 25,000 burning hours. Using the same with low ESR and ripple factor, the driver's life may be enhanced. The driver should have high efficiency and power factor of more than 0.85 with THD not more than 50%.

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