Thirty years ago, the most interesting thing I knew of was the digital watch. Never mind that digital watches were harder to read than analog watches, that they went through a set of batteries every few weeks, that they cost a small fortune. These things were not important. What was important was cutting-edge style. You could now wear a computerized device on your wrist that, at the press of a button, would display the time in glowing red LED numerals! How cool was that? When my dad got his first digital watch—a huge, clunky thing—I was deeply envious that he had the best toy in the house.

Just a few years later, though, digital watches had moved into the mainstream. I distinctly remember, as a nine-year-old in 1976, saving my allowance to buy my very own $20 digital watch. I was the first kid in my school to have one, the envy of all my friends. (Yes, my geek roots go way back.) It would be a few years yet before liquid-crystal displays (LCDs) became common; in the meantime, I was thrilled to have a status symbol courtesy of LEDs.

Since their commercial introduction in the 1960s, LEDs (light-emitting diodes) have become common components of every imaginable household product. Your phone, TV, answering machine, clock, and possibly even your kids’ shoes have LEDs in them. LEDs are popular largely because they’re inexpensive and use very little electricity. Compared to ordinary incandescent bulbs, LEDs also produce less heat, last many times longer, and are less sensitive to shock and changes in temperature. These are all wonderful attributes, but until relatively recently, there was one major limitation: color. Your choices were limited to red, amber, and green; anything further along the spectrum just didn’t exist. The invention of the blue LED was groundbreaking, but the white LED that soon followed was cooler by an order of magnitude.

A Little Light Science
To understand why white LEDs are so cool, you need to know a little bit about the technology behind LEDs generally. A diode is a very simple semiconductor device that allows electricity to flow in just one direction. If you apply current in that direction (called forward-biasing), the diode produces light as a side effect. For ordinary diodes, that light is infrared, invisible to the naked eye. By varying the materials used in the diodes, scientists were able to produce diodes that made visible light—red at first, and later, other colors. The physics behind LEDs dictates that whatever light is produced is of a single wavelength (that is, a single color). But for a long time, nobody could figure out how to make colors with shorter wavelengths than green—at least, not at any reasonable level of brightness.

Among the people trying to solve the blue LED problem was Shuji Nakamura, a researcher at Nichia Chemical Industries in Japan. Nakamura thought he had determined just the right type of material (indium gallium nitride, if you care) to use for blue LEDs. The problem was that the existing manufacturing processes did not produce material of sufficient quality. So he had to invent a new process as well. In 1993, after years of research, Nakamura finally produced the first commercially viable blue LEDs.

Now with Extra Whiteners
This achievement alone would have earned Nakamura a place in electronics history. But the real genius was in his next step. He applied a special type of phosphorescent coating to a blue LED. The blue light excited the molecules in the coating—much like the way a fluorescent lamp works—and produced bright white light. So white LEDs are actually a clever spin-off of blue LEDs, and without Nakamura’s insights, neither would have been possible.

A white LED is brighter than a comparably sized, conventional incandescent bulb. However, it’s not as bright as a high-output Krypton or Xenon bulb, such as you’ll find in fancy flashlights. In addition, white LEDs cannot be made arbitrarily large, as incandescent bulbs can. So if you want to replace the bulb in your Mag-Lite or kitchen light fixture, you must use a cluster of LEDs. A good LED flashlight will typically have three or more bulbs; for residential lighting, much larger clusters are used—for example, a 36-LED fixture will replace a 30-watt bulb; to replace a 90-watt bulb would require over 100 LEDs.

Apart from the issue of sheer luminosity, an important reason for using LED clusters is the pattern of light they produce. With incandescent bulbs, the light is omnidirectional, which is why flashlights and lamps usually have reflectors to concentrate the light in a certain direction. LEDs, because of their built-in lenses, produce much more directional light. This can be either a blessing or a curse, depending your needs. If you want to create a “Walk” sign at an intersection, an array of white LEDs will give you just what you’re looking for: bright light with a fairly narrow viewing angle. If you want to illuminate a room, however, that directionality is a problem. LED fixtures that need to disperse light more broadly rely on a combination of varying angles for individual LEDs and light-diffusing coverings.

The Price Is White
Although red and amber LEDs can be purchased for just a few cents each in volume, blue LEDs, which are harder to manufacture, typically cost about ten times as much, and white LEDs are more expensive still. You might imagine that a 100-LED fixture to replace your hall light would be quite costly, and you’d be right: at current prices, that sort of light will run you well over US$500. Of course, over its lifetime, which will probably be decades, you will save quite a bit of money in both electricity and replacement bulbs. This is precisely why they are attractive to municipal governments, which are rushing to replace conventional bulbs in traffic lights (and in some cases streetlights) with LEDs.

Until economies of scale bring white LED prices down to more reasonable levels, their biggest appeal for ordinary consumers will be in products such as flashlights, bike lights, and headlamps used for caving. It’s in applications like these that the LEDs’ low power consumption makes a profound difference. A Krypton flashlight might run for three hours on a set of alkaline batteries, compared to thirty or more for a flashlight using white LEDs. The extra convenience, not to mention the cost savings, can be enormous.

This Little Light of Mine
A bit of additional circuitry can extend the life of LED-based products even further. For example, I bought a white LED flashlight called an EternaLight. It has a built-in microprocessor that flashes the LEDs very rapidly—so fast that the human eye cannot detect it. Because the LEDs only use power when they’re actually on, this technique stretches the battery life to as much as 700 hours—you could leave the flashlight on for a full month. After about three years of frequent intermittent use, I decided to change the batteries simply on principle because I was going on a trip, but for all I know they could have lasted another three years.

There are many reasons to like white LEDs, but for me, the sheer cleverness of the idea tickles my fancy. The novelty has already worn off, but I’ll always be impressed by the creativity and hard work that made them possible. And when some pseudo-retro designer gets the idea to make a white LED digital watch, I’ll be first in line to buy one. —Joe Kissell

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More Information about White LEDs...

For a good discussion of how LEDs (though not specifically blue or white ones) work, visit HowStuffWorks.com. Articles on Nakamura and the process he invented can be found at EE Times and TechWeb, among many other sites, and an interview with him was published on ScienceWatch.

The LED Light.com sells every conceivable white LED product (other colors too). If you want to replace every bulb in your home, RV, and flying saucer with white LEDs, these guys can do it. And yes, they do sell drop-in replacements for Mag-Lites (AA size).

The EternaLight, which comes in a variety of models, is sold by Technology Associates. I love mine and would heartily recommend it to anyone. If you follow this link to make a purchase, Interesting Thing of the Day will receive a small commission.

Amazon.com also carries a great many white LED products in such categories as sports and outdoor living.

Related Articles from Interesting Thing of the Day

• Brain Machines
• Global Energy Network
• Light Pollution
• Automatic Transmissions for Bicycles
• The Color Purple

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When I was about 12 (give or take a couple of years), I had what I thought was a fantastic idea. I was going to build myself a volcano. I’m not talking about a little model made out of clay with vinegar and baking soda for the special effects. I wanted to construct a dirt cone in the backyard that was hollow inside and large enough to use as a clubhouse. I was a bit sketchy on the actual structural details, but I figured I’d start by digging a nice big pit, then add some sort of frame and cover it over with the dirt I’d removed previously. So I got an old piece of garden hose and formed it into a circle about 15 feet (5m) in diameter on the lawn to mark the perimeter of the volcano. The actual digging turned out to be a lot harder than I’d imagined—so hard, in fact, that after shoveling about two scoops of dirt I decided I’d better take a break. Weeks later, when I still hadn’t resumed my project, my mother told me to get that hose out of the middle of the yard, and while I was at it, mow the lawn. Reluctantly, I put the hose away, only to find it had left an unsightly yellow ring on the grass. It looked as though a flying saucer had landed, and the ring didn’t fade until the following spring.

I was embarrassed at both my inability to build my volcano and the condition of our lawn. It never occurred to me that with a bit more effort, I could have turned my blunder into a huge piece of art—say, a smiley face or a basketball. Just as well; I think my parents would have frowned on that. But nowadays, grass art—based on the very same principle I unwittingly discovered—has reached an exceptional level of sophistication, as artists create giant, stunningly detailed photographs on living grass.

The Grass Is Always Greener
When grass gets plenty of sunlight, it produces chlorophyll and therefore turns green—but the less light it receives, the more yellow the color is. British artists Heather Ackroyd and Dan Harvey discovered that by projecting a bright black-and-white negative image onto a patch of grass as it grows (in an otherwise dark room), they can use the natural photosensitive properties of the grass to reproduce photographs. When I saw one of these grass photos on display at a museum, I was utterly captivated. From a distance it looks like any other monochrome photograph (albeit with a slightly unusual tint); up close, it looks like perfectly ordinary grass. But even individual blades sometimes have a range of hues, as any given cell can respond to the amount of light it receives.

Ackroyd and Harvey stumbled onto this technique after producing an installation that involved covering an indoor wall with living grass. A ladder was leaning against the wall, and the artists noticed that even after it was removed, a faint outline of the ladder remained on the grass. They set about experimenting with ways of enhancing this effect, and soon they were using a slide projector as an artificial light source for growing their unique photographs. A typical exposure time is just over a week, with the image projected for 12 hours a day.

It’s an Art and a Science
At first, the grass photos faded within several days, as the grass adapted to the light conditions in the place where it was exhibited. Ackroyd and Harvey began looking for ways of increasing the longevity of their images, and they found a genetically modified strain of grass called stay-green. Engineered by researchers at the Institute of Grassland and Environmental Research (IGER) in Wales, stay-green grass cannot break down chlorophyll easily and thus retains most of its green color—even after it’s dead. When using stay-green grass as their medium, Ackroyd and Harvey dry out their grass images rapidly as soon as they’ve matured. Although this kills the grass, the images remain visible for years, rather than days.

The IGER scientists working on stay-green grass were impressed with the artwork to which their product had contributed. And while looking at some digital images of the grass artwork, they came up with yet another innovation—a noninvasive way to study the chemical changes in the pigments of leaf cells as they age. Their technique, called hyperspectral imaging, relies on a computer to analyze colors that are too similar to be distinguished by the human eye. So science contributed to art, which in turn contributed to science—and sure enough, this additional research has inspired the artists to explore new creative directions.

Ackroyd and Harvey have done grass art installations all over the world. They are especially proud of the fact that although their medium is by nature temporary, the images can be regrown at any time. Some of their most famous pieces have been recreated several times already. If I ever have enough money to commission a work of art, I’m going to ask them to grow me a photograph of a volcano. —Joe Kissell

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