The Evolution of a Small Plastic Bulb

LED lighting systems are ideal for extended operation because of their low power requirements.

SINCE the dawn of man, fire and light have beaten away the dark. A lit torch meant the difference between living and falling prey. Ever since Edison invented the light bulb, flashlights, like all technology, have progressed from a simple momentary torch to a sophisticated lighting instrument that is integral to safe plant operations. Imagine being in a blackout without a flashlight. Activity on the assembly line, in the lab, or in a burning building, interrupted by a failing flashlight, can be problematic at best and life threatening at worst.

The incandescent bulb was once the preferred way to light a flashlight. In the past 15 to 20 years, LEDs have steadily gained in technology and popularity for their safety, extreme battery efficiency, toughness, versatility, and brilliant collimated beams. Where did these bits of plastic and semiconductors come from, and how did they become so important?

Flashlights and LEDs have different yet parallel histories. The advent of white LEDs has revolutionized the way flashlights are built. "I think LEDs have definitely sparked the evolution of flashlights, as well as video sign boards and auto interior illumination," said Craig Johnson, founder of LEDmuseum.org. An LED, or light emitting diode, is a plastic light bulb that produces illumination and photons by the movement of electrons through an embedded semiconductor material. In the simplest terms, an LED is made with two different kinds of semiconductor material: one type that has too many free electrons roaming around inside and another that doesn't have enough. When an electron from one material (the donor) gets pushed across a thin barrier and fits into tiny spaces in the other (the holes), a photon or particle of light is produced. From the early 1900s to the 1930s, researchers used zinc and phosphorous to create a low-level light effect called electroluminescence, but it was too faint to be used. Several different experimental versions of the LED were created, but not until the 1960s did the first modern LED, emitting only an invisible red light, become available. This was the basis for the first remote controls.

Starting with red in the early 1960s, LEDs climbed the spectrum to pale green and yellow. The mid-1990s saw the birth of the first super bright LEDs using gallium nitride (GaN) and indium gallium nitride (InGaN) as the basis for emerald green, cyan (blue-green), blue, and later, violet and UV LEDs. This, in turn, led to the development of the white LED. The white LED is coated with phosphorescent phosphor to absorb the blue end of the spectrum. This shifts the spectrum down to yellow/green, which mixes with residual blue to create a bluish white light. "It was only 10 years ago that the best light LEDs were capable of was in VCR, calculator, and watch displays, so they've come a very long way in a very short time, technologically speaking," Johnson explained.

Why LEDs?
There are four important reasons:

* LEDs have up to 20 times the life of incandescent bulbs.
* LED systems are ideal for extended operation because of their low power requirements.
* LED use about one-tenth the power of incandescent bulbs and are up to 90 percent more efficient than both fluorescent and neon lamps of similar strength.
* LEDs don't burn out like bulbs and require less maintenance.

"The inherent advantages that LEDs have over common incandescent bulbs--long life, shock resistance, full-color light--make them a natural choice as a replacement. Just a couple of years ago, we saw LEDs appear on the market which could produce 10 times the light of the previous generation of LEDs," said Doug Pribis of www.flashlightreviews.com.

LEDs offer big safety and maintenance benefits. In tests conducted at two U.S. Air Force bases, military firefighters used smoke machines to fill a room. LED flashlights made it possible for firefighters to read the words on a compressor at the opposite end of the room, whereas other flashlights could not penetrate the smoke particles clearly enough.

The normal working lifetime of an LED device, including the bulb, is 10 years, lasting much longer than that of most other light sources. LEDs can fail by dimming over time, giving them a distinct advantage over the abrupt burn-out of incandescent bulbs. They also give off less heat than incandescent bulbs and are much less fragile than fluorescent lamps.

Incandescent bulbs are cheap to buy but inefficient to run. They generate a range of about 16 lumens per watt for a domestic tungsten bulb to 22 lumens per watt for halogen bulbs. Fluorescent tubes are bulky, fragile, and require starter circuits but can give large energy savings, weighing in at about 50 to 100 lumens per watt for domestic tubes. LEDs are tougher and much more efficient than the common incandescents, with the average commercial LED generating about 32 lumens per watt.

Unlike incandescents, LEDs do not need a filter to absorb most of the emitted white light. Today's white LEDs are made with a single blue LED chip that has been covered with a phosphor that glows a yellowish color when exposed to the blue light from the LED chip.

The overall result is a super bright LED that produces a white to bluish white light. Generally speaking, white LEDs are exactly the same as the blue LEDs. They have the same voltage and current requirements because white and blue use an almost identical chip.

Early Flashlights
The first flashlights were hand-made from crude paper and fiber tubes, with a bulb and a rough brass reflector. Because early batteries were weak and bulbs primitive, flashlights of the era produced only a brief flash of light--earning them the name "flashlight."

In 1899, the first truly portable light was invented in the form of a clover-leaf bicycle light. As battery technology improved (slightly), the lights could be turned on for a few minutes (instead of moments) and could be made in smaller sizes. The 1906 introduction of the tungsten wire filament replacing carbon filaments in light bulbs made them more efficient and brighter.

Flashlight technology took a leap forward in 1910 and paved the way for modern flashlights with the introduction of nickel-plated tubes to complement vulcanized fiber and the invention of the tungsten filament bulb. Among the first portable light technologies to become popular were vest pocket tungsten flashlights, search lanterns, house lamps, and intricate art deco candle lamps. The first tactical application came when they were given to the New York Police Department for field tests.

Fast forward to 2001, when the first LED flashlights were created using LEDs in an aluminum casing. The generated light was too soft and diffused to make them useful for anything but close-quarters lighting. "There were a lot of homemade LED lights in the '70s and '80s, but the first commercially manufactured LED lights I reviewed were the CMG Infinity Task Light--Photon 2 Microlight in early 2000. They were useful for close-range task lighting of six feet or less, but incandescents at that point still blew them out of the water, brightness-wise," said Johnson.

Recently, the LED technology has been refined into high-powered, one- to three-watt lighting instruments broadcasting a brilliant collimated beam. And there is a sea change happening with the LEDs. Their beams can now be focused and brilliant with the help of engineered reflectors. The latest in LED technologies offer bright light and consistent color in a very small package, generating as much as 45 lumens per watt in white for a one watt. Today's one-watt LED is about equal to 10-20+ ultra-bright white 5mm LEDs while occupying the same or less space. A recent advance shines a single one-watt LED backward at a parabolic mirror to capture 100 percent of the generated light, raising the bar for LED lights and ushering them into the professional marketplace as viable alternatives to incandescent bulbs.

Pribis, author and owner of flashlightreviews.com, said he sees an incredible future: "I expect that LED lighting technology will continue to grow at an exponential rate. I would not be surprised if within the next several decades, most of the man-made light we encounter in our lives is produced by energy-efficient, full-spectrum, solid-state LED 'bulbs.' It's only a matter of time until we see LED bulbs producing 10, 100, and 1000 watts' equivalent of light."

From a simple cardboard tube and a dollop of plastic with wires running through it, LED flashlights have become and will continue to be one of the most important parts of plant and safety operations today.

This article appeared in the September 2005 issue of Occupational Health & Safety.

This article originally appeared in the September 2005 issue of Occupational Health & Safety.

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