White led

WHITE LED

Presented by:- Atul Gupta 13474 E&CED

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With 20% of the world's electricity used for lighting, it's been calculated that optimal use of White LED lighting could reduce this to 4%.

Use of White LED will reduce the release of CO2 into the atmosphere by a significant amount.

White LEDs are Energy efficient.

Long life (A typical White LED lamp can last for 100,000 hours).

Motivation

CONTENTS• Introduction• Working Of LED• Colors• How is White light made with LEDs• White LED structure• Advantages• Disadvantages• Future Scope• Conclusion• References

Introduction• White LEDs, or white light–emitting diodes, are semiconductor

devices that produce white light when an electrical current is passed through them.

• Light emitting diodes (LEDs) were first developed in the 1960s, but it became possible to develop white LEDs only after the invention of Blue LED in 1992.

• White Led lamp is the fourth and latest generation of white light sources after:-

1. High intensity discharge(HID) lamps2. Incandescent bulbs and3. Fluorescent bulbs• A 1.2 watt white LED light cluster is as bright as a 20-watt

incandescent lamp and lasts 25 times longer.

Working of LED

• The LED is a semiconductor diode that emits light when current passes through it• The n-side is heavily doped• When forward biased, the built-in potential at the junction is reduced• The e- from n-side get injected into p-side• e- combine with the holes resulting in emission of photons i.e. light• This effect is called electroluminescence

• Light is characterized by frequency, or more commonly, by wavelength• Visible light spans from 400 nm to 700 nm• White light is a combination of this mixture.

Colors

Colors (cont.)

The Noble Prize

• Isamu Akasaki and Hiroshi Amano of Japan and U.S. scientist Shuji Nakamura won the 2014 Nobel Prize in physics for the invention of blue light-emitting diodes.• They produced bright blue light beams from their semi-conductors in

the early 1990s, and triggered a fundamental transformation of lighting technology. Red and green diodes had been around for a long time but without blue light, white lamps could not be created. Despite considerable efforts, both in the scientific community and in industry, the blue LED had remained a challenge for three decades.

How is white light made with LEDs?

Presently, there are two approaches to creating white light.

1. Mixed color white light

2. Using Blue LED with phosphor coating

Mixed-color white light:

• One approach is to mix the light from several colored LEDs to create a spectral power distribution that appears white.

• By locating red, green and blue LEDs adjacent to one another, and properly mixing the amount of their output, the resulting light is white in appearance.

Mixed-color white light (cont.)

Advantages• Excellent Color Rendering (faithful color reproduction)• High lumens/watt• Color temperature can be tuned by adjusting the three colors separately• More efficient compared to phosphor based LED

Disadvantages• Difficult to achieve pure white color• difficult to maintain color stability over life and at different operating

conditions

Phosphor-converted white light: Another approach to generating white light is by use of phosphors together with a short-wavelength LED. For example, when one phosphor material used in LEDs is illuminated by blue light, it emits yellow light having a fairly broad spectral power distribution. By incorporating the phosphor in the body of a blue LED with a peak wavelength around 450 to 470 nanometers, some of the blue light will be converted to yellow light by the phosphor. The remaining blue light, when mixed with the yellow light, results in white light.

Phosphor-converted white light (cont.):-

Advantages• Temperature Stability• Simpler to create than the RGB LED• Decent colour rendering

Disadvantages• Less efficiency• Weak lumens/watt• Short life time compare with other type of LEDs

Phosphor-converted white light (cont.):-

WHITE LED STRUCTURE

Good efficiency & durability

Advantages Of white led

• LEDs can provide 100,000 hrs of life compared to 1000 hrs with incandescent light bulbs

• Associated with perfect material and devices, LEDs would require only 3 Watts to generate the light obtained with a 60-Watt incandescent bulb

Figure 1. LED vs. conventional light sources degradation in light output over time

Good stability• Due to their solid state, they can withstand vibrations better and have no filament that might break

• They are capable of functioning in many environments.

•They are robust in nature.

Advantages (cont.)

Reduction in energy consumption

• LEDs require less current than incandescent bulbs

• Comparison with incandescent bulbs: When cold, an incandescent filament draws ten times as much current as it does during normal operation. The initial powering of hundreds of incandescent bulbs simultaneously causes significant voltage surges that lead to lamp failures.

Advantages (cont.)

Reduction of heat emission

• Less heat emission Lens stays cooler Less energy wasted

• Room temperature stays cooler, so we don’t need further air conditioning

• Some LED lamps are designed with series resistors to limit the operating current, resulting in no cold filament current variation.

Advantages (cont.)

Allows wide variety of lighting• Artificial lighting similar to daylight

• More control of the color and intensity

• Interesting design possibilities: they can be placed on floors, walls, ceilings or furniture!

Advantages (cont.)

Result double environment-friendly

• Less current consumption (less electricity burned)

• Less heat produced

Less CO2 emissions.

Less light pollution.Non toxic as do not contain mercuryPositive impact on global warming.

Incandescent traffic lights replaced by LEDs in USA:economy of2.5 billion kWhours= US$ 200 million= 3 billion kilos of CO2 released in the atmosphere

Advantages (cont.)

DisadvantagesCost Competitivenes:- White LED prices are significantly higher than that of incandescent light bulbs.Temperature dependent:- Since the wavelength of light is directly proportional to the junction temperature, White LEDs have to be operated on same current biasing.colour rendering properties of cool white LEDs are insufficient for some applications.

Future scope• In the past 6 years, White LED has seen tremendous gain in

energy efficiency, brightness and lifespan. For now efficiency is between 25 to 50%, but is expected to reach 90%!

• Companies are trying to find new methods of generating white light. A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs. This has reduced the cost. It is predicted that by 2020, 40% of all GaN LEDs will be made with GaN-on-Si.

Estimated White LED market growth in India.

Future scope (cont.)

Conclusion

Given the remarkable technological innovation of the past few years, it is expected that market expansion will bring further improvements in LED luminous efficiency, and further cost reductions. The range of uses will surely continue to increase, not only for white LEDs but also for LEDs of other colors, within the context of saving energy and the need for thinner designs.

References • https://en.wikipedia.org/wiki/Light-emitting_diode• http://

www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/whiteLight.asp• http://www.lighting.philips.co.in/lightcommunity/trends/led/• http://www.omslighting.com/ledacademy/570/ • http://

scitation.aip.org/content/aip/magazine/physicstoday/article/54/12/10.1063/1.1445547• http://energy.gov/eere/ssl/led-basics#how_efficient