Lighting and illumination
has recently faced a major sea change in that it is no longer purely an electromechanical discipline. The advent of electronic
illumination technology driven by light-emitting diodes
s) and Electroluminescent
have created a new market segment, Solid-state Lighting and Illumination (SLI).
Once upon a time, the only way you could create light was to make something hot. Eventually, electroluminescent chemicals such as phosphorus were found. Edison's bulb (the industry still calls screw bulbs edison-base lamps) was only a refined manifestation of the proverbial caveman's fire. Noble-gas lamps and neon tubes use glowing gas. A variation in the incandescent light, fluorescent lamps are coated in the inside with phosphors that glow when bombarded by UV light created by stimulating a gas mixture (usually mercury and argon with an electric current.
The world changed when Nick Holonyak invented the first LED in 1962. At first, only long wavelengths of light could be generated, which is why the first devices were red and amber. When the white-light LED was convergently invented by Cree and Nichia, the real revolution began.
All of those glass-based lamp solutions using hot filaments or energized gases are not only bulky, they are also fragile. Made of tiny silicon chips, LED lamps are far more robust. For street-light applications, LEDs satisfy energy conservation requirements while providing broad-spectrum light. LEDs are very directional, so they also minimize off-axis light leakage.
On the issue of operating lifetime, most incandescent lamps die within several thousand hours of operation. Most LEDs last over a hundred thousand hours. Think of the money saved in replacement and maintenance. That's the reason LEDs are already taking over traffic and street-sign applications. Solid-state lighting provides so many advantages that incandescents will eventually (~10 years)become niche products for specialty applications.
Previously, the optoelectronics industry was primarily driven by laboratory research. Lasers, sensors, and optical communications were the primary outlets of this sector. The market has changed radically, however, and a large portion of the industry is now specifically targeted for consumer devices. What was once a bent-metal electrical industry is now a surface-mount technology (SMT) electronics industry.
There are three major areas of interest for SLI lamps: Traditional lighting, Displays, and Device lighting. Traditional lighting involves the lights we have around us every day, from desk lamps to office lighting to the lights around you home. Display lighting includes LCD backlights as well as projector light engines.
LEDs provide a significant advantage in illumination of Liquid-Crystal Displays (LCDs) and microdisplay-based projectors. Since Red, Green, and Blue LEDs are literally from the corners of the chromaticity scale, they provide not only "whiter" light, they also make colors more vivid in such displays to the tune of up to 115% of the NTSC color standard.
According to one estimate, LED-based display backlights are expected to reach a market size of $2.7 billion by 2009, and the LED lighting market is predicted to be worth up to $3.9 billion in 2010.
The SLI segment is by necessity a cross-discipline industry. No longer can a company just stick a light bulb into a socket and call it a day. Both LED and EL lighting require driver electronics (including logic), thermal management, optics, and packaging.
Electronics: Because LEDs and EL both require voltages and currents specific to the type of emitter, color of emission, and brightness of the light desired. The power input from outside the device, be it battery or wall socket, must be controlled and managed in a very specific fashion in order for SLI devices to work.
Thermal: Although SLI devices are much more efficient than incandescent bulbs, as flat emitters on a substrate they have poor thermal performance. A filament can dump its waste heat into its surroundings, but an LED leaks most of that heat into the substrate it is constructed on. Heat sinks and fans are used in high-output SLI devices.
Optics: An incandescent bulb is called a Lambertian emitter. That means it is treated as a point source that emits light in every direction. The light from LEDs is highly directional, and EL is highly diffused, so lenses, light guides, and reflectors are needed to create the desired illumination pattern.
Packaging: The electronics package, emitter, thermal management materials, and optics must all be packaged in a container that presents the smallest outline with the best optical and thermal performance.
The rise of the SLI industry is providing opportunities to manufacturers both at the bleeding edge of technology and in mature segments. “Old-school” manufacturers of heat-sinks, incandescent bulbs, power supplies, and plastics have found new life by applying their strengths to the new challenges in creating SLI devices.
-Thanks to XWiz, filoraene, and TenMinJoe for asking good questions.