Light emitting diodes (LED) is one of the emerging energy-efficient lighting technologies that pack huge potential as a popular light source of the future. However, it is still too early to conclude if LEDs will replace the existing light sources without first overcoming several major technical hurdles.

Although the LED was first lit in 1968, it did not evolve into a marketable product until the mid-1980s, when the technologies to make blue and white LEDs were introduced. Such technologies enable the diodes to give off a full spectrum of colors.

Continually upgraded technologies mean that manufacturers are able to find niche and specialized applications for the LEDs. Today, LEDs are built into traffic lights, outdoor billboards and various products; but over 80% of the diodes are adopted for the most lucrative applications, including handsets, automobiles, consumer electronics, household appliances, displays and billboards.

Such applications have allowed heavyweight manufacturers of high-powered LEDs to generate serious profits, including Cree, Lumiled and Nichia. Nichia, a LED-chip and phosphor-powder maker, has even taken steps to protect its lead in the market by setting up a threshold with patents.

Featuring upsides and downsides
LEDs are noted for many merits, including lightweight, low starting voltage, energy-efficiency, quick start-up, zero pollution and durability. With significantly improving illumination efficiency and color-temperatures ranging from 3,000K to 11,000K, white LEDs is seen as an ideal light source that can replace incandescent and fluorescent lamps for lighting small areas.


With energy conservation being a relevant issue globally, LEDs and their inherent characteristics make them green-sensitive products. Industrially-advanced countries estimate that lighting consumes around 20% of world energy, so energy-efficient LEDs can help reduce such usage once they replace tungsten and fluorescent lamps en masse, at the same time help to curb emissions of greenhouse gases.

However, the reality of replacing existing light sources with LEDs dims in light of the many technical hurdles.

Theoretically, white LEDs have estimated life-spans of 100,000 hours; but the illumination tends to decline 50% after 15,000 to 40,000 hours, with 30~50% shortening of life-span if used under high heat.

The market researcher Laser Focus World optimistically estimates the LED illumination efficiency to be 200 lumens-per-watt (lm/w) and can help trim US$35 billion in energy spending globally in 2025, an unrealistic scenario considering the current efficiency of commercial white LEDs have an average 40-lumens-per-watt.

LEDs remain expensive, around 20 folds higher than the existing light sources both in price and cost. Such disadvantages are keeping the global market share for LEDs to under 10%, which may upset Strategies Unlimited`s forecast that the market of one-watt highly-bright LEDs will grow 14% annually, to US$7.2 billion by 2009.


Although over the past four years many international lighting heavyweights have tried to impress the lighting industry with their unique LED lighting fixture designs and applications; while regional lighting manufacturers have worked very hard to develop LED lighting fixtures, the LED lighting fixtures market, especially that of high-powered outdoor lamps and general indoor lamps remain small. One reason,
in my opinion, is that most of the LED lighting fixtures are unviable products; because the manufacturers often have foggy ideas regarding LED engineering. Some LED-lamp makers do not even have a firm grasp of lux and candela.

Not ready to take over
Undoubtedly, LEDs have niche applications, but they are not ready to take over the entire lighting market for the following reasons.

In the near future, LEDs` illumination output efficiency is unlikely to reach the 120 lm/w rating of fluorescent lamps, noting however that a single LED`s maximum power output is five watts and a commercial LED light delivers an illumination efficiency of 35-40 lm/w.

Such slow pace of development might disappoint the forecasts by the Optoelectronics Industry Development Association (OIDA) of the United States, a non-profit agency of the optoelectronics industry; and the Japanese LED industry. The OIDA predicts white LED`s efficiency to reach 75 lm/W next year and 150 lm/W by 2012, as well as replacing incandescent lamps next year due to considerable cost declines. Japan has even targeted to replace fluorescent lamps with LEDs by 2012.

Although fluorescent lamps use mercury, a toxic substance, such hazards has been partially addressed by using solid mercury, which makes replacing fluorescent lamps with LEDs less urgent.

LED is criticized for its low lumen output with a weak beam or luminance, a major factor behind its tendency to glare. Such characteristics make it unsuitable for auto headlamps, since headlamps must have bright, focused beams to offer drivers clear vision in darkness. Therefore an array of LEDs have to be crammed onto a 10cm x 10cm headlamp module, resulting in ultra high glaring, which is a visual hazard for oncoming drivers.

For the time being, LEDs are unsuitable as desk lamps. To generate the minimum 500 lux of light required by industry standards for desk lamps, five to 10 LED lamps are needed for one light. However, the area effectively lit is less than 25 square centimeters, insufficient for prolonged reading.

Also LED lamps remain pricier than fluorescent and incandescent lamps. A marketable LED desk lamp must be on a par in terms of retail price to a fluorescent lamp.

LEDs are still less desirable and hence inferior in terms of color-rendering and color-temperature relative to fluorescent and incandescent lamps. For example, white LEDs usually have a color temperature of around 6,000K, a cold-white light that is ghostly compared to the cozy warmth of a conventional light bulb. So LEDs may simply be too "cold" to outshine incandescent if not fluorescent lamps.

Those who vow that LEDs are sure to replace incandescent and fluorescent lamps should review the history of incandescent lamps, which were never sidelined by fluorescent lamps as had been predicted.

Despite that incandescent lamps are electricity guzzlers, they are popular in high-latitude countries, and of course fowl farmers depend on the heat given off to incubate eggs. LEDs can not duplicate the warmth generated by incandescent lights.

Only when the color-rendering and color-temperature characteristics of LEDs match those of fluorescent and incandescent lamps can they become a household light source. Meanwhile, LEDs are already widely used for their desirable features in traffic lights, billboards, emergency lights, and ornamental lighting.
(This article is by Dr. Hsiao Horng-ching, an electrical-engineering scientist at the National University of Science and Technology, and translated by Taiwan Lighting reporter Ken Liu.)
(by Ken)