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Shedding Light On LEDs

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Shedding Light On LEDs

Governments are making a concerted effort to convert our homes and public spaces to LED lighting. Dr. Dipankar of Treelabs-IIT Bombay, explains the technology behind these diodes and if this switchover is a good move.

 

Delhi has become the first city to roll out a plan that will convert conventional home lighting to LED bulbs. On March 1, power distribution companies began offering two LED bulbs to their customers  at Rs. 10 per bulb with an EMI of Rs. 10 in the bills over the next year. The government hopes to convert all homes to LED by 2016 which will allow it to save up to 250 million units (mu) or 1% of the total power consumption.

 

In the west, the Maharashtra government too plans to replace older sodium vapour street lights with LED bulbs. Lights along Mumbai’s iconic Marine Drive were the first to be changed in the month of February. This move drew criticism from many quarters including the Shiv Sena, which is part of the state government. The criticisms ranged from “destroying the look of the Queen’s necklace” to low visibility and dark patches along the stretch.

 

As is with most new technology, LEDs are more expensive than traditional lighting. An 8 watt LED bulb which provides lighting equal to a 60 watt traditional incandescent bulb costs roughly 40 times more at between Rs. 400-600.

 

It is in how long LEDs last that the advantage lies. An LED bulb can last for nearly almost six years as compared to an incandescent one that lasts for about a year.

 

This drive to replace incandescent  and CFL bulbs with LEDs  begs the question: are LEDs the solution to India’s energy needs? If one speaks to experts like Dr. Dipankar who is an Innovator Engineer, Scientist and Professor at Treelabs, an invention centre at IIT Bombay  explains that there are two parts to this effort of trying to become more energy efficient. He says, “LEDs—light emitting diodes are solid state devices that use electricity to give out a range of colour bands that together combined make up visible white light. If one compares LEDs to the traditional bulbs, then bulbs use part of the electricity to give out heat which does not happen in LEDs.  But, power efficiency is also about how one uses the available energy. Most of us, especially Indians light up our homes in the evening and each room has at least two CFLs if not more. So energy conservation cannot just be seen through the prism of replacing the fixtures.”

 

The Science Behind LEDs

 

LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescent bulbs, they don’t have a filament that will burn out, and they don’t get hot. They are illuminated solely by the movement of electrons in a semiconductor material. The LED uses a small semiconductor crystal with reflectors and other parts to make the light brighter and focused into a single point. LEDs create light by electroluminescence. Electroluminescence is the phenomenon of a material emitting light when electric current or an electric field is passed through it – this happens when electrons are sent through the material and fill electron holes. An electron hole exists where an atom lacks electrons (negatively charged) and therefore has a positive charge.

 

Semiconductor materials like germanium or silicon can be “doped” to create and control the number of electron holes. Doping is the adding of other elements to the semiconductor material to change its properties. By doping a semiconductor you can make two separate types of semiconductors in the same crystal. The boundary between the two types is called a p-n junction. The junction allows current to pass through it only in one direction, this is why they are used as diodes. LEDs are made using p-n junctions. As electrons pass through one crystal to the other they fill electron holes. They emit photons (light). Different materials create different colours and differently coloured LEDS have different voltage and current requirements—a green LED may consume more (or less) power than a blue one. However, white LEDs and blue LEDs don’t occur naturally. Blue LEDs are made out of a special junction of Indium and Gallium; White LEDs use blue LEDs with a phosphorus covering that make it resemble white.

 

Diverse Application

 

The LEDs have a distinct advantage that they can be miniaturized. Tiny LEDs have already replaced the tubes that light up LCD HDTVs to make thinner televisions. LEDs are also low-voltage light sources, requiring a constant DC voltage or current to operate optimally. Operating on a low-voltage DC power supply enables LEDs to be easily adapted to different power supplies, permits longer stand-by power, and increases safety. Hence, the use of LEDs lamps powered by solar panels are an option to bring light to parts of rural India that are yet to get 24/7 electricity supply.

 

Is it really eco-friendly?

 

LED bulbs, especially those above 8 watt include a component called a heat sink, a ribbed aluminium segment that is attached to the bottom of LED bulbs. Aluminium heat sinks absorb and later dissipate heat that’s generated by the light bulb, preventing it from overheating. The process to mine, refine and process the aluminium in heat sinks is energy-intensive and creates several byproducts such as sulfuric acid that must be taken to a hazardous waste landfill. But research is ongoing to improve the manufacturing process of LEDs.

 

A disadvantage of LEDs mentioned previously is that they are directional which means they emit light in a specific direction, unlike incandescent and compact fluorescent bulbs, which emit light and heat in all directions. Hence to replicate lighting of CFL bulbs, multiple LEDs have to be installed with the right diffusers or luminescent materials that allow the spread of light. Prof. Dipankar explains, “For lighting purposes, the directional property of LEDs is a disadvantage as they need many components to accompany them. But because they are directional, it means they are great for situations where you need focused lighting.”

 

Even though  governments seem to be driving the use of LEDs, Prof. Dipankar flags off a concern.  With a majority of the patents for LED technology held by six global companies, prices may remain high. The real solution to energy efficient lighting technology has to come from disrupting traditional ways of using light as well as finding new forms of illumination.

 

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