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Thirteen quick questions about LED.

The development of LED has been rapid and is considered by many to be the future of lighting. With promises of increased energy efficiency, extended lifespan and the associated environ-mental benefits, it’s really no surprise it is the subject on everybody's lips.

We want to look beyond the hype and promotion to provide straightforward answers to a selection of frequently asked questions (FAQ’s). These are some of the key questions that arise on a daily basis and there is clearly a need for information about how LEDs can be used to create commercially viable environments.
By taking this approach, we hope to provide an overview of the technology and how it can be implemented within a retail lighting scheme.

1. What is LED?
LED stands for Light Emitting Diode. An LED is not a traditional light source; it is a semiconductor that emits light. Nor is it a “new technology”. As early as 1927 a Light Emitting Diode was presented in a Journal by the Russian scientist Oleg Vladimirovitj Losev. Although this was not the first, it was the first report to be widely circulated. The first LED with a visual spectrum was developed in 1962 by Nick Holonyak Jr, who is often seen as the “father of the light-emitting-diode”.

An LED consists of a semiconductor with coating on a small plate which, depending on the material used, emits different types of light when a current is passed through the diode. The light emitted is the result of a physical phenomenon known as electroluminescence.

2. How does it work?
In a normal incandescent lightbulb, you can use either a direct current (DC), or an alternate current (AC). An LED is a semiconductor and only uses the direct current, which necessitates the polarity also being in the right direction. This principle is referred to as forward voltage. If the polarity is wrong, or backwards, nothing will happen, similar to the same principle as a non-return valve in a water pipe. When the forward current flows through the diode, the electrons fall into holes with lower energy levels, or junctions, releasing energy in the form of photons; light radiation.

 

3. How long is the lifetime of an LED and its driver?
The manufacturers of LED’s and their drivers claim 50,000 hours, defined as the LED operating at more than 70 % of its output. While this is not a formal standard, it is the level, or criteria, being used throughout the lighting industry.

4. What about heat radiation?
It is widely believed that, when using an LED, there will not be any heat radiation within the beam. This is not entirely accurate as there is a very small amount of heat radiation. While it is barely noticeable heat is produced. Compared to a traditional light source, which is cooled by the atmosphere, an LED requires a more advanced and engineered heat management system. When transforming any energy from one form to another form, e.g. electrical energy to visual light radiation, there is always a large amount of redundant energy that is always transformed into heat in one way or another.

5. Is the LED an energy efficient light source?
The energy savings from an LED are not yet fully as significant as is often reported in the media and promotional materials, which compares the technology with incandescent or low voltage halogen (dichroic) light sources.When comparing with HID (High Intensive Discharge lamps) there is still a lot to do. When looking only at the efficacy of lumen/wattage, the LED is really good in comparison with HID. But if we look at the efficacy for the entire power conversion of electrical energy into a viable visible light, it is a completely
different situation.

6. How is the LED light source recycled?
LED light sources are essentially electronic components consisting of PCB materials, diodes, semiconductors etc, so the methods used are the same as traditional electronics. They have to be collected separately from household waste and must to be treated like standard electronic equipment.

7. Is LED a sustainable light source?
LED is a very sustainable light source due to its high efficacy and long life potential, with the efficacy of LED chips continuing to increase dramatically. Well-established LED sources, commonplace in the market today, can deliver products with a system efficacy of more than 60 lumens per watt in a high quality warm white light (including losses accrued through the driver and thermal management).

Furthermore, their directionality means far greater optical efficiency than traditional sources when combined with optics such as lenses or reflectors. The required light effect can therefore be achieved with a lower source efficacy. LEDs with cooler white light are even more efficient and can be used when this light is deemed acceptable for the application (refrigerated display lighting is a good example of this). In addition, LED products are capable of extremely long lives when engineered correctly.
The above numbers represent today’s state-of-the-art from commercially available products. LED technology continues to develop quickly however, and laboratory figures of >200 lumens per watt are now being quoted from some of the major manufacturers. These LEDs are not currently commercialised.

One note of caution is that the benefits of LED, with respect to sustainability, are only achievable if proper attention is paid to how the LED is embodied and engineered into the product and application in which it is to be used. To do this, a good understanding is needed into how a given LED package performs under different conditions.


8. When can I completely use LEDs in my store?
You can. Although the appearance of the light radiation from each type of light source is very specific. As such, the basis for selecting the most appropriate light source should be driven by the type of installation, application and the type of light required.

9. How can I integrate LED into my existing lighting solution?
That depends on what type of lighting solution there is. While it is possible, it is not always the most efficient way to do it. Often it will require a complete overhaul of the lighting solution as simply retrofitting the luminaires can compromise the light quality.

A large number of the retrofit LED light sources on the market today are of varying quality. Most of them act as a replacement for dichroic (HRGI) up to 50W and for other types of halogen lamps. Some are also possible to dim. They can work well where the requirements for light output, light quality and efficiency are slightly lower than
normal, for example in domestic environments.

10. How can I have the same rendering with LED as with my current technology?
With existing technology, the only way to achieve this is by using a module with a large number of LEDs with different wavelengths to cover the entire visual spectrum.
This approach is not only costly but it also places high demands on heat management and space.

11. Can I change the light source into an LED and keep the fixture?
With some low voltage fixtures yes, but problems can emerge depending upon the suitability of the transformer for LED modules.

12. Why is LED so expensive?
LEDs are still being produced in relatively small volumes compared to other materials (e.g. silicon wafers) and, consequently, don’t enjoy the same economies of scale.
Increasing the global LED volume and capacity is key to decreasing their cost and delivering lower price for a given light output. In addition, a good LED product requires significant additional engineering to ensure reliability and consistency of performance.

13. How will LED develop in the near future?
An enormous increase in efficiency to ~150 lm/W is anticipated at component level and a reduction in the price to less than €1 for 100 lm in 2012. LEDs in the future will also differ from their 2012 counterparts in terms of higher driving current and densities, standardisation and a large number of application oriented products for different environments.
Over the next few years, LEDs are predicted to continually increase in efficacy. Some distributors have LEDs from leading manufacturers under qualification in laboratory that, if proved to be reliable, will lead to further dramatic efficiency increases, up to 50 % compared to the current best available technology. Even this would still leave some way to go for further improvements. For general lighting, the market will evolve with more standardised LED packages, light engines and modules for
different applications.

There will also be dramatic improvements in quality of light thanks to developments in phosphor technology. Packages will evolve that can retain their efficacy at higher drive currents, making higher lumens possible from small source sizes. This will allow even better optical control and the opportunity to reduce the number of lumens needed for the desired light effect. Finally, there will be a greater focus on system developments, with smarter LED drivers, more dynamic lighting (colour change, dimming) and remote management systems all being developed further and specified in greater quantities.