Research & Development

Revlite's engineers and designers are constantly striving to improve the efficiency and light output of their designs. Why? Because at this point in time, we are at the forward edge of a lighting revolution - the LED Revolution.

What is the LED Revolution? What are LED's? How did it start?

What are LEDs? (Light Emitting Diodes)

First of all LEDs unlike regular filament bulbs (or gas filled tubes) are semiconductor devices that create light using solid-state electronics. Like transistors, and other diodes, LEDs are crystals of silicon composed of a layer of electron rich material separated by a layer of electron deficient material which form a junction. Power applied to this junction excites the electrons in the electron rich material leading to photon emission and the creation of light.

When it comes right down to it what makes an LED give off light are the small amounts of chemical impurities that are added to the silicon, such as gallium, arsenide, indium, and nitride. These impurities are added to the silicon in a specific recipe (in a process called doping) that determines the colour of the light given off by the LED. Depending on the chemical composition of the semiconductor layers, the color of light emission will vary within the electromagnetic spectrum. This is why LED's are available in so many different colours. In essence the manufacturer can tailor the hue of the LED.

When a current is passed through the LED junction, it emits photons as a natural byproduct of the electron transfer. LEDs produce photons directly and not via heat therefore they are far more efficient than incandescent bulbs.

What makes LED's so much more efficient than Incandescent bulbs?

There are a number of reasons. First let's look at how an incandescent bulb produces light. Ever since Edison's day they have remained essentially the same.

First an electric current is passed through a conductor while the conductor is housed in an evacuated glass envelope. The conductor or filament has resistance and it is this resistance to current flow that causes it to heat up to the point that it starts to glow and give off light. This is similar to what happens when a welder heats up metal with a torch - it glows red or white hot - The higher the temperature the whiter the light. (This is why most incandescent bulbs give off a yellowish cast and not a true white light.)

Essentially an incandescent bulb is a space heater that gives off light as a byproduct of heating. This requires high energy consumption.

The LED on the other hand requires only a minute amount of current to excite the silicon crystals and their impurities to give off photons.

LED's also produce light in only a narrow bandwidth which is determined by the chemical recipe that is added to the silicon crystals. This means that all of the energy given off by the LED is light energy in a very specific colour rather than wasted energy in a broad band of colours. In a white LED there is no wasted energy given off in the infra red or ultra violet range as is the case with the incandescent light bulb.

LED's have an optical system built in which directs the light to where it is needed instead of the shot gun approach of the incandescent bulb. Most LEDs have a clear epoxy lens which directs the light energy in a beam of 8-15 degree angle so it may be placed exactly where it is needed. Other LED's have other lenses that spread the light for use in diffuse applications.

Not long ago LEDs were only bright enough to be used as indicators on dashboards or electronic equipment. But recent advances have made LEDs bright enough to rival traditional lighting technologies. Modern LEDs can replace incandescent bulbs in almost any application.

Why do LED's last so long?

As mentioned earlier a regular incandescent bulb produces light by heating up a filament until it glows white hot. This heating expands the metal and all of the fittings inside. When shut off the element cools and sags. The repeated heating and cooling cycles stress the filament until fatigue sets in and it breaks (typically 1000-2000hrs).

The LED on the other hand does not have a filament and when switched on the electrical current simply excites the electrons in the junction to jump to the next energy level releasing photons at that time. Since there are no mechanical components there is nothing to fatigue and fail.

The lack of a filament solves another problem in that LED's are perfect for lighting objects that move or vibrate. The regular incandescent bulbs in automobiles for instance will typically fail in less than 1000hrs due to vibration acting on the filament.

Try this experiment. Take a fresh incandescent bulb - say a 100watt. Install it into a table lamp. Grasp the lamp firmly at the bulb and now with the side of your hand hit the base of the bulb firmly without breaking the glass. Now turn on the lamp. The light will probably go on and then quickly flash out because the filament has been fatigued by the hit. This will never happen to an LED.

Typically an LED can burn continuously or cycle on and off for 50,000 to 100,000hrs. That's 50-100 times longer than an incandescent bulb!

Where can I see them in use today?

Chances are you've been stopped more than once by an LED. Have you noticed them? By now, you may have noticed that crosswalk signals have gotten a lot brighter, and a lot whiter. At the same time, traffic lights have become pixelated and more clear. It's all part of the LED revolution that's sweeping cities and companies alike, saving energy and huge amounts of money in the process.

Have you looked closely and noticed the change in stoplights. The regular incandescent light bulbs are being replaced by super efficient LEDs (light emitting diodes.) The stoplights look like a cluster of small dots of colored light. This is the front edge of a coming revolution that looks to replace familiar light bulbs with long lasting high efficiency LEDs.

The HB (High Brightness)-LED Revolution... It started with red spectrum HB-LEDs for use in automotive brake lights, which helped prevent accidents by turning on faster and with higher brightness, making recognition easier for other drivers. The revolution continued with applications in red and yellow traffic signal lights resulting in significant savings in energy costs. More recently, gallium nitride (GaN) semiconductor materials made the impossible possible by allowing HB-LEDs to generate the unique blue-green colors of "go" lights worldwide. Then came tiny white GaN lamps in flashlights, which were small enough to fit on a key chain and guaranteed for life.

Next, due wholly to the availability of commercial HB-LEDs in all colors, huge video screens the size of buildings, now capture the eyes and minds of sports fans, commuters, pedestrians, and concert crowds around the globe. Now, power-frugal white GaN HB-LEDs are creating light in places never thought possible such as remote third world villages equipped only with pedal-powered generators. The possibilities are expanding as HB-LEDs are becoming brighter and less expensive every year.

Today, HB-LEDs are being designed into all manner of applications where small size, low voltage, low maintenance, long life, power savings, color control, brightness control, directivity, and durability are needed. It's hard to think of a place where at least one of these benefits is not needed! Light, as we know it has changed. High Brightness LEDs are the driving force behind the shift away from incandescent, fluorescent, and neon "standard" bulbs, this will enable designers to let there to be light where there was no light before.