Articles and whitepapers

LED Lighting Technology (4/4/2005)

By Martin Barker, Lutron EA Ltd

The first Light Emitting Diode (LED) for general lighting use has been a long-time coming, but its introduction gives us a glimpse into the future of lighting.

Up to this point, the use of lighting electronics had been reserved for the devices controlling the light itself, in the form of electronic transformers for low-voltage lamps and electronic ballasts for fluorescent lamps.

LEDs have been around for years and feature on most electronic devices as indicator lamps. The LED was initially selected as the ideal indicator light source because of its long life, low cost compared with a conventional lamp, reduced energy consumption and low heat generation.

Recent advances in the form of the blue LED and higher output variants have resulted, for the first time, in a truly usable light source for producing colour-changing effects. In addition, claims are already being made that this new generation of LEDs for lighting will eventually replace the energy-saving fluorescent lamp and common light bulb. So are these LEDs really useable, and if so, where?

LEDs for lighting definitely have a 'new toy' factor to them, which is always dangerous and beguiling. So let us consider when and where to use them. The use of LEDs generally falls into two camps: 'colour changing' achieved from single-colour LEDs and 'white light'.

Colour changing LEDs create a tranquil ambience at the pool, Marriott Hotel, London

Colour Changing

Colour changing, when applied correctly, has a certain 'wow' factor about it. To change colour, the system takes monochromatic light sources in the form of red, green and blue LEDs (RGB) and uses a technique called 'colour adding' to produce the final colour required. Sounds great until you consider that sodium streetlights are also monochromatic. Have you ever tried to check colours under these lights? Shades of orange look fine, but other colours appear lifeless and dull. This is because only the colours that match the light being emitted are picked out. Now use the same principle and bathe the dining table with blue light. Blue lights on carrots? Not very appetising!

To get the best from coloured LEDs, washes on white surfaces and the use of back-lit panels will ensure maximum effect with minimum distortion.

Automated colour changing LEDs in backlit panels.

Controlling colour changing LEDs

Colour changing LEDs can be controlled in a variety of ways. In their simplest form, colour changing systems are pre-programmed like Christmas-tree lights and will operate when switched on. The next level of control is manual selection of colour changing speed, sequence selections and fixed colour choice. Various options are also available for integrating colour changing systems, and generally use external controllers to provide signals to the LED driver that delivers power to the LEDs.

As a colour changing system is essentially a theatrical solution, it often uses the theatrical standard protocol called DMX. In order to generate DMX codes, a control system is required - typically a lighting control system or some other control system that generates DMX code. Alternatively, it is possible to use a DMX storage device to store pre-designed DMX shows which can, in turn, be triggered by contact closure or RS232. For AV integration, the RS232 option can in some instances provide a valuable feedback function, allowing a system to operate a fail-safe scenario in the event of the LED system not operating properly.

If all this seems too complex however, a 0-10v system can be used. Although primarily used for many years to dim fluorescent lighting, the controller provides the signal to the LEDs to change colour, which is ideal where limited sets of individual RGB groups are to be changed. However, when each set of RGB LEDs is to be controlled in order to achieve colour chasing along the line or pulsing of colours, the control will almost always have to be to DMX.

Still too complex? Or thinking about something else? Then have a chat with a quality lighting controls company. It will be able to provide a path through the potential minefield and provide you with the solution to match your and your client's lighting requirements.

White LEDs

Although they promise to eventually provide superb optical control, energy saving and very long life, white LEDs, despite the acres of press coverage and the many products on offer, currently provide few real benefits. The current generation of white LEDs provide higher outputs than previous versions, but are still less efficient than the humble light bulb, let alone the fluorescent lamp that they seek to replace. But it is not all bad news.

The good points are that they can be built into smaller luminaries, although care should be taken to ensure good heat transfer from the light fitting, otherwise permanent damage or failure will occur. They can be great for applications where a marker is required or an area is to be highlighted. Indeed provided the ambient level is low, the LED offers a great, often dramatic, solution.

White and colour changing LEDs used for architectural lighting

For the keen-eyed users amongst us, the white LEDs offered in luminaires do have a very cold blue appearance. This can provide a good contrast with the warm appearance of light bulbs, however it is worth checking before buying, as the contrast could be too great, or the effect appear too cold.

Colour rendering

If white LEDs are required to render colours accurately, then look elsewhere or increase the proposed budget significantly - high colour-rendering white LEDs can be bought but they are rare and costly. Where the electronics industry has produced a good single-colour product, it has still to perfect the uniformity of quality we get from light bulbs or fluorescent lamps. Hundreds of identical lamps could be lined up together and no variance seen between them, however this is not possible yet with LEDs. This consistency will happen over time, but only as the product develops from an electronics product into a lighting product.

Light levels

If you are thinking of using white LEDs to light residential areas to lighting levels normally associated with LV halogen, light bulbs or fluorescent lamps, beware! You will require many more LEDs to achieve these levels, which in turn will cost much more to buy and use several times more energy to operate.

All hype and no benefit?

The LED for lighting has some great features, but has not yet reached its full potential. As an electronic component, we should expect the doubling of performance in terms of light output every couple of years. We can also expect to have some industry-defined outputs relative to wattage as with other light sources. This will greatly assist maintenance and move away from a situation where nearly every new installation is a 'one-off'.

One day the LED will probably be the only light source we use at home. In the meantime, we should ask ourselves what we want to achieve and then look at the ways of achieving it - LEDs may indeed provide the correct solution. Just make sure the reliability, light output, control, energy consumption and maintenance questions have been addressed first.

As with all exciting new technologies there are some pitfalls for the unwary. Experienced companies however, can provide excellent products that provide long-lasting innovative solutions. Once you have the product, be sure to remember the control system, as it provides the key to the versatility and flexibility of your installation. After all, you will almost certainly wish to change the lighting levels in scenes over the long life of the product. As with all custom installation systems, it is how they integrate and how they are controlled that ultimately provides the magic.

Martin Barker is the Territory Manager for Lutron lighting controls across Scandinavia. He has over 15 years experience within the lighting industry, specialising in the application of technical products including LEDs and lighting controls.

www.lutron.com