Lighting the 21st century

More recently, Color Kinetics has developed Chromasic, a single ASIC that integrates its Chromacore system onto a single chip. And a recently awarded patent describes LED-based lighting networks as a means of wireless communication through a local-area network.

Light from nature

LEDs with standard lamp bases were once only competition for tiny miniature and subminiature bulbs called T1 or 3-mm bulbs. Today, they come in a wide variety of standard lamp bases, in sizes ranging from T1 to medium-screw 25-mm G30-sized bulbs and larger.

While LEDs have moved from indicator lights to sources of illumination, another quiet revolution is stirring in the world of displays. Organic LEDs, or OLEDs, have begun displacing older display technologies such as liquid-crystal displays (LCDs) and cathode-ray tubes (CRTs).

OLEDs are made by sandwiching layers of organic thin-film material between two conductors. An applied voltage recombines the positive and negative charges in the layers producing light through electroluminescence.

The big advantage over LCDs is that OLEDs are self-luminous and don't need backlights. This cuts power usage significantly and makes for a thinner overall package. OLEDs also have a wider viewing angle, up to 160°, compared with other flat-panel displays, and have faster response times to keep up with real-time video.

More importantly, OLEDs can be manufactured on flexible substrates such as plastic and metal foil. This means future displays can be bent or rolled up like a newspaper. For starters, however, OLEDs will most likely challenge LCDs in PDAs, digital cameras, computer monitors, and television screens.

There's quite a bit of activity in the OLED arena. One example is a venture called the Flexible Display Initiative (FDI), funded in part by the Army Research Laboratory. The aim is to research and develop a flexible display for use in military applications with target field demonstrations set for 2007-2008.

The Luxaura lighting system from Bridgestone Industrial Products, uses an LED light source and a reflective strip integrated into a clear, solid acrylic light guide. It mimics neon and fluorescent tubes but doesn't require the associated high voltages and fragile glass. They've found uses in automotive applications such as the Lincoln Blackwood for truck bed illumination and in Toyota's Harrier SUV for interior console lighting.

One thing is clear; the LED revolution has just begun. So sit back and enjoy the light show.

Sidebar: Measuring light

There are a few oddities and nothing standard about LED specifications. Some manufacturers provide output in candela, others in lumens or milliwatts. The lumen is a photometric measure, milliwatts are radiometric, and candela measures maximum intensity or brightness. But candela is a subjective, murky unit. For instance, suppose all the light from a source is focused down to a narrow beam. This doesn't change the actual light output or the number of photons, but the apparent brightness has increased.

The lumen/watt, the SI unit commonly used for measuring the total amount of light emitted by a light source per energy input, doesn't accurately reflect true efficiency. LEDs are directional light sources and emit little or no spherical light. But the lumen/watt unit takes into account all light emissions from a light source, including spherical, and not just what is actually accomplishing the required illumination task.