Light-Emitting Diode (LED) Technology and Applications
There have been great leaps in efficient lighting in recent decades, from the traditional incandescent to halogen to compact fluorescents. The next technology on the horizon is light-emitting diodes (LEDs).
LEDs were introduced in the 1960s, but high costs limited them to a few niche applications such as on/off indicators on home and office electronics. There have been great advances in recent years, and LEDs are being commonly used for traffic signals, vehicle brake lighting and exit signs.
There are many advantages to LED lighting, the greatest being efficiency. Many LEDs offer 90 percent efficiency, compared with 5 percent for traditional lighting sources. This represents significant cost advantages to consumers and reduced greenhouse gas emissions that contribute to climate change.
Other advantages include:
- long life
- low heat dissipation
- improved visibility
- resistance to shock and vibration
- reduced maintenance costs
- vivid colours
- high luminous intensity
- compatibility with integrated circuits
- compact size and light weight
The many potential applications for LEDs are only just being explored. These include street lighting, seasonal lighting, commercial signage and indoor/outdoor residential lighting. LEDs will not only revolutionize how we light to see, but how we see lighting.
Technology Profile on LED
Light-emitting diodes (LEDs) life span and flexibility are just some of the features that set LEDs apart from other light sources.
How Do LEDs Work?
An LED is a semiconductor device (diode) that emits light when an electric current passes through it. The diode produces a monochromatic (one colour) light on a single wavelength ranging from red (˜700 nanometres) to blue-violet (˜400 nanometres). Because LEDs produce a pure colour of light, tinted lenses are not needed to filter the light to the desired colour. As a result, all of the visible light is projected from the LED.
LEDs consume very little power – they are up to 90 percent efficient, which means that only a small proportion of the input energy is consumed to produce heat. In comparison, traditional light sources (e.g., incandescent bulbs) are 5 to 10 percent efficient, with 90 percent or more of the input energy wasted in the form of heat.
Another type of LED currently under development is made up of semiconducting organic polymers. These organic LEDs (OLEDs) are only about 10 percent efficient but are expected to be less expensive to manufacture than regular LEDs.
A Little History
The first LED – a diode emitting yellow light – was developed by Henry Joseph Round in 1907. This early version was too dim to be useful, however, and it was not until 1968 that visible red light was emitted through a diode.
Over the years, diode technology was improved to create more colours and to increase the brightness of the light projected. Until the 1990s, however, high production costs limited the use of LEDs to a few niche applications, such as "on/off" indicators for home and office electronics.
Today, LEDs that produce red, green and amber light are a proven technology that can generate significant energy, operating and maintenance cost savings. As the purchase price of LED products continues to decline, their use is growing. LEDs are now used in many applications, including traffic lights, exit signs, flashlights, outdoor lighting, tunnel lights, seasonal and display lighting, automotive lights, roadway lighting, commercial signage and more.
Researchers are continuing to develop a cost-effective white light that will allow LED technology to compete with other light sources in the lucrative residential and commercial markets.