LED

 LED`s......

History of LED

Let us look at this journey of LEDs through which they triumphed over the Lighting world.It was 1962, when Nick Holonyak Jr. invented first visible led, emitting red light, while working at General Electric. As the light output of these LED’s was not enough to illuminate the surrounding area, but were good enough to be used as indicators and hence Indicators, seven segment displays were some initial applications followed by being used  in appliances such as calculators, watches, TV, telephones.

With the help of similar alloys, more colours green, yellow were manufactured by mid 1970’s.

The ongoing research in LED technology brought superior ones with improved efficiency and light output. In early 1980’s LED were being used for messages and other outdoor applications. They used less power and were ten times brighter than previous ones.

With improved performance, applications and market penetration began to rise. By early 1990’s High brightness LED packages were developed and were widespread used in Traffic lights.

A remarkable milestone was achieved in mid 1990’s when Dr.Shuji Nakamura of Nichia chemical Corporation invented high brightness GaN blue LED. It was this LED that paved path for the development of white LED when coated with phosphor. By this technique white LED’s were produced by 1993.

This was the pre phase of the giant leap of LEDs, which made it possible to use them for illumination by invention and development of high power white light LEDs.

Today LEDs have reached performance levels far exceeding previous projections. Market expectations have increased and a wide range of applications including facade lighting, general purpose illumination

Inside the little light House:

The way these tiny blinkers light up is far different from the traditional counterparts. For understanding its outstanding capabilities, we need not dig deep but just our fundamental concepts of Semiconductor diodes.

When a PN junction diode is forward biased, the electrons and holes move in opposite directions. During this free movement, an electron may fall into a hole which exists at a lower energy level than electron, because of this an electron loses some energy which is released in the form photon and hence light is emitted. This phenomenon is termed as Electroluminescence.

Now this emitted light may or may not fall in the visible spectrum depending on the material of semiconductor. In silicon diode, the energy gap is not much wide and hence the emitted photon of low frequency is falls in infra red region (Infra Red LEDs). But in case off our little blinkers, the semiconductor material used is Aluminium Gallium Arsenide (AlGaAs) and later on various similar alloys. The colour of emitted light depends on the energy gap of semiconductor. 

 

 

Creating White Light:

LEDs are not white light sources. They are highly efficient monochromatic light emitters, which is the reason they rule the coloured light applications such as traffic signals, exit signs etc.

For LEDs to be used for general purpose illumination, white light is needed. Mainly, there are two ways of achieving white light from LEDs:

·   Mixing of monochromatic lights red, green, and blue to white light.

In this method, multiple wavelengths (RGB) are mixed to produce light. This technique is same as employed in television sets in which a white spot is created using red, blue and green light in proper proportion.

The creation of white light by mixing colours has additional advantage of tuning it to a specific colour temperature to look warm or cool. The Colour temperature rating of a lamp is a general ‘coolness’ or ‘warmth’ measure of its appearance, termed as Correlated Colour temperature. It is measured in Kelvin. The white led spectrum ranges from 2540K-10,000K. Cool white, warm-white, neutral-white are some of the categories depending on varying colour temperature. Designers can choose the suitable colour temperature as required. Lamps above 4000K are generally categorised as ‘cool’ while those below 3200K as ‘warm’ in appearance.

 

·   Second method is Phosphor conversion, in which a phosphor is used on or near the LED to emit white light. This method uses a blue Indium-Gallium-Nitride (InGaN) LED with a phosphor coating to create white light. The coating emits a yellow light when the blue light from the LED shines on it. The mix of the yellow light with the blue light forms a white light. This is the method that results in the more commonly seen “white LED”.  It is the amount of inefficiency in phosphor conversion due to some energy loss in the conversion that makes white light LEDs less efficient than coloured LEDs.

LED (SSL) - What makes me Unique??

The little blinker is glowing on famous buildings, bridges, hotels all over the world. This is indeed a remarkable advancement, as it not just evolved and changed but is now changing the way world lights up!

Solid State Lighting is realized when LEDs are combined with well designed luminaries. Let us dwell into depth and find the factors that made the buzz of Solid State Lighting all around.

So what made LEDs to be used for general illumination purpose? LEDs being inherently monochromatic light sources were not even considered as an option for general lighting purpose (which requires a dedicated white light source) until Shuji Nakamura invented the high brightness blue LED, which can be used to produce white light. Since then, there has been noteworthy improvement in the performance of white light LEDs. Light output, control, efficacy, optical design, lifetime have been improved to make them competent with conventional light sources. Also, the increasing efficacy (the amount of light provided in lumens, per watt of electricity consumed (lm/W) in last decades has contributed significantly for the same. The energy performance of LEDs is continuing to improve dramatically and has approached 100 LPW in the production of white LEDs. The development of LED technology has caused their efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s, in a way similar to Moore's law.

The following factors focus on some more reasons for wide acceptance of SSL.

· Energy Efficiency

At a time of escalating energy crisis, the less efficient sources are bound to move out of the market replaced by more efficient solutions. Same is the fate of incandescent sources. LEDs can cut the general lighting energy use by one quarter.

Energy Star rated LEDs use at least 75 percent less energy than traditional incandescent bulbs and last 25 times longer, according to the U.S. Department of Energy. A 1.3-watt LED bulb uses less electricity than both the 60-watt incandescent and the 9-watt CFL bulb. The way LED produces light does not involve energy loss as heat while Incandescent and CFLs release most of their energy as heat, 90 percent and 80 percent, respectively.

LED lighting will eventually replace halogen bulbs. It is said that a typical 50 watt halogen lamp will produce 22 lumens per watt of energy that is produced. As well as this, the bulb will last for around 2,000 hours. When we compare this will a typical LED light, it will actually produce the same amount in terms of lumens but it will only take 7 watts. This is a huge energy saving. As well as this, the bulb will last 50,000 hours compare with 2,000.

US Department Of Energy’s long-term research and development goal calls for white-light LEDs producing 160 lumens per watt in cost-effective, market-ready systems by 2025

· Go SSL- Go Green!

The little energy savers do make a BIG difference, having the potential to cut general lighting energy uses by one quarter saving energy dollars and carbon emission too.

 

The annual Co2 reduction is much significant even for a single bulb. The feather in the cap is its long life. Moreover, it does not contain mercury like CFLs. In many applications, the reduced energy requirement extends the running time of battery operated devices like notebook computers, mobile phones and also reduces petrol consumption and CO2 emissions. Also, their long lifetime minimizes service requirements in many applications.

·   Directional Emission

One of the unique characteristics of LEDs is their directional light emission. When light is emitted in specific direction, it reduces the need of reflectors and diffusers to trap light.  Fluorescents and incandescent emit light in all directions, out of which some amount is lost within the fixture, escapes out in unintended directions or get reabsorbed. In some cases even 40-50% of energy gets lost even before it exits the fixture.

While in case of LEDs, cleverly designed fixtures can deliver light efficiently in intended direction, for example, LED strip lights can be installed under counters, in hallways, and in staircases; concentrated arrays can be used for room lighting.

·   Long,LongLife

Now you don’t need to change the bulbs or CFL again and again, go the LED way and forget to change it for next 20 years!! Sounds imaginary...Right?

Here unveils one more miracles of LEDs.  The life of incandescent lamp is about 1000 hours and that of a CFL is nearly 8000 to 10,000 hours. On the other hand, LEDs offer much higher lifetime of 30,000 to 50,000 hours in well-designed fixtures. Some claims even go higher up to 70,000 hours with 70% lumen maintenance.

LED lights are more rugged and damage-resistant than compact fluorescents and incandescent bulbs. Also, LED lights don't flicker.

Not only it lives longer, but reduces your electricity bills up to 7%

Lighting Quality

The quality of lighting can be evaluated on certain parameters like:

·   Colour Appearance: i.e. whether a white light appears more yellow/gold or more blue. It is measured by Correlated Colour Temperature (CCT), which is a specification of the colour appearance of the light emitted by a lamp, relating its colour to the colour of light from a reference source it is measured in Kelvin scale. For most interior lighting applications, warm white (2700K to 3000K) and in some cases neutral white (3500K to 4000K) light is appropriate.

·   Colour rendering Index: CRI is a measure of the degree of colour shift objects undergo when illuminated by the light source as compared with those same objects when illuminated by a reference source of comparable colour temperature. Generally, a CRI of 70 and above will be required for most lighting applications.  The leading high-efficiency LED manufacturers now claim a CRI of 80 for phosphor-converted, warm-white devices but the CRI of RGB LED system has found to be inaccurate.

Applications

The substantial progress in SSL has made headway for its use in diversified applications. 

·   Industry:  Industrial sites operating 24/7 consumes huge amount of energy. Also, it becomes very tedious and affect the operation too when the lamps need to be replaced in their super high ceilings. Of course, a solution that does not need frequent maintenance and reduces energy consumption without compromising the light level is worth opting for.

·   Offices: SSL moves parallel to the changing tastes in world class design.  They provide freedom to choose different shapes, designs, dynamic effects in intensity and direction, colours. They effectively create better work places along with significant energy savings, especially when combined with lighting controls.

·   Retail: They are increasingly used for retail outlets as they can be used to create suitable scene for every occasion, be it highlighting a product or create perfect shopping environment by employing effects to enhance the shopping experience.

·   Outdoor Spaces: LEDs provide an unparalleled way of illuminating our urban environment in an exciting and practical manner. They are highly adaptable, allowing designers to move away from the static lighting of the past and venture into creating flexible ambiances that could, for example, change with the weather or the season, and  provide an extra festive colour on public holidays. And all this with energy consumption that is only a fraction of conventional lighting techniques.

Challenges

The upfront cost of LEDs is the major challenge faced by SSL for coming to general house hold lighting applications.  LEDs can cost two to six times the price of CFLs. Good-quality LED products currently carry a significant cost premium compared to standard lighting technologies. However, with ongoing research advancements and increased acceptance in various applications, the costs are coming down. Less brightness is also an issue, but ongoing research has even started suggesting promising solutions for it too. Organic LEDs and nanotechnology are offering better and much improved solutions.

OLEDs: The Bright ‘Organic’ Future

Even after the giant leap, the little LEDs still have long way to go. After wide acceptance for inorganic LEDs, it’s time to explore the ‘Organic’ way.

New research is focussing on alternative materials like organic polymers to develop what are called as Organic LEDs. These LEDS are not just eco-friendly to dispose of, but also generates photons of various wavelength ranges to help to produce white light. New improved designs are also being developed to produce much bright white light.

Another proposed technique for brighter LEDs is Nano-imprint lithography to directly imprint the holes, imperceptible to the human eye, onto the LEDs allowing more of the light to escape. By making microscopic holes on the surface of the LEDs it is possible to extract more light, thus increasing the brightness of the lights without increasing the energy consumption.

Their unique characteristics like lack of infrared or ultraviolet emissions, long life and ease of maintenance, good performance in cold temperatures, resistance to breakage and vibration, compact size, and instant-on performance make them the inevitable option for tomorrow.

We await the new Energy Efficient and Eco friendly solution to light up the globe.