From small acorns...

But what are leds and why has there been this sudden upsurge in interest?

LEDs – the technology
LEDs are semiconductor devices that emit light when connected in an electrical circuit. In general they consist of a small semiconductor chip mounted in a reflector cup on a lead frame. This device is encased in an epoxy bulb, which serves as a lens, concentrating the light through the rounded tip.

The colour of the light transmitted by the led depends upon the type of semiconductor material used. The ability of such materials to conduct electricity varies, the rate of conduction determining the colour produced. Red has been the easiest colour to produce traditionally, with white the most difficult.

"They originate from indicators," explains Dominic Meyrick, principal of Hoare Lea Lighting, "where a fit and forget item was needed." LEDs have no moving parts and no glass or filaments that can be broken or wear out. They shouldn't fail, just fade over time. This makes them ideal for areas with poor accessibility. Their lifespan depends on the led colour and the operating conditions; white leds typically operate for 30 000 hours, red leds under the same conditions could provide 80-100 000 h; a standard incandescent lamp will typically operate for 1500 h. The general industry standard to indicate the end of an led's life is when the light output has reduced by 50%. "All other lamp sources are mechanical, so break," stressed Meyrick, "LEDs last massively longer because they were developed to not need changing."

The reason that leds remained in the indicator market for several decades was down to light output – it was not possible to efficiently produce sufficient light for large-scale applications. Advances in technology is changing this and opening up the market opportunities. With increasing intensities and reliability, and low power consumption, the move into commercial lighting has begun.

"The intensity has doubled every 18 months for the last five years," explains Meyrick. "Seven years ago there was a dramatic increase in the light output and efficiency of leds due to new [semiconductor] materials," confirms applications specialist Colin Beale of Osram Opto Electronics. "Over a period of a few months, ten times the light output of earlier devices was possible. LEDs then became viable for lighting applications."

Greenwich-based Light & Design Associates was reportedly the first practice to use leds as a light source in a UK commercial application, installing a light sculpture in a Ferrari showroom.

"We've been working with leds for the last two to three years," confirms director Lee Prince, but warns: "I see it as another tool in the box for lighting design rather than a catch-all panacea. In the right application they are great but they're not for everything."

One of the current setbacks for large-scale uptake of leds in lighting schemes, concur Prince and Meyrick, is the availability of suitable luminaires. Prince states: "Some manufacturers are putting leds into housings that do not disperse the light, or into small reflectors, which make them more powerful, but more expensive if you're trying to use them as a light source. I'd like to put out a cry to manufacturers to be discerning about the implementation of leds in products."

The manufacturers' response
With light outputs growing to practical levels for lighting, so is demand. Lighting manufacturers report rising interest, particularly from the signage industry, and increasingly from designers, attracted by their versatility and intense colours.

This interest has seen manufacturers seeking to utilise the knowledge of established led producers. Osram Opto Electronics, for example, was formed following a joint venture between Osram and a Siemens division that specialised in the technology. The firm is now a wholly-owned subsidiary of Osram.

Philips Lighting followed the same path when it saw the opportunities for leds and has formed a joint venture with Agilent Technologies, producing led products under the name Lumileds. Mark Van Den Berg, marketing manager for Lumileds Europe explains: "It is difficult for companies like Philips to start producing their own leds. Agilent had 40 years of experience." These firms are among those now developing products for the lighting industry.

"Within the next 12 months we are likely to see a dramatic rise in the number of lighting products in the market," states Osram's Colin Beale. As these product ranges increase and the leds specifications improve in terms of efficacy, output and colour properties, the potential applications will rise.

Thorn Lighting's Hugh King explains: "LEDs are proving popular but are not a mainstream lighting product at the moment. They are mostly being used in signage and architectural lighting for retail and effect areas.

"The technical issues are being addressed by manufacturers, with light output increasing monthly, but it's got to go up a quantum jump before becoming a mainstream product," says King.

Van Den Berg predicts this jump to be imminent: "We are currently getting 25 lumens/W [led output], but expect this to double over the next two years. This will open up lots of applications where today, halogen and incandescent lighting is used. It will start by being used next to it but will then take over, although halogen is unlikely to disappear completely."

The firm has recently produced a 5 W led that it is aiming at the domestic lighting market. Whether this market is yet ready for such products is uncertain.

As with all technology, costs can prove the ultimate factor in uptake. The price of semiconductors is reported to have plummeted over the last decade, but with leds, the seeming fall in cost is also linked to rising outputs. Beale explains: "Individual unit costs have not fallen, but the efficiency [hence light output] has gone up dramatically. Applications two years ago may have had to use twice as many leds as they would for the same job now, so the relative cost has fallen."

With the number and quality of products constantly rising and client interest being aroused; lighting installations using leds could soon become commonplace.