The Light Bulb at a Critical Time of Change

The logic behind the lighting provisions in the Energy Independence and Security Act is pretty forthright: Incandescents convert less than 10 percent of the energy sent into them into light, losing the rest as heat. More-efficient bulbs could save billions of dollars, reducing dependency on foreign oil, and particularly reduce greenhouse gases.

Still, the consumer backlash booms, and not simply because CFLs are terrible, not very compatible, ugly, and unreliable. Evolutionary biologists think that human lighting preferences are the result of our trichromatic vision – rare in nonprimates – that makes us suited to daylight and the perception of primary colors. There’s an anthropological element as well: For 400,000 years, humanity has been banishing darkness with fire. And Edison’s light bulb is, at its root is a burning filament that casts the luminosity of a flame. Abandoning incandescent bulbs means leaving fire as our main light source for the first time in human history.

GE created the light-emitting diode in 1962. The first ones to appear in wide use – glowing a space-age red- turned up in the clock radios, calculators, and digital watches of the 1970s. Over the next couple of decades, additional colors came along.

LEDs are constructed more or less like any other semiconductor. Each diode is cut from a wafer of crystals coated over a base of silicon or sapphire. The crystal coat on early LEDs contained gallium arsenide or gallium phosphide, which gave the red-ish color.  Additional colors and improved brightness needs more control of layer composition and depth. Modern LED manufacturers achieve this by using precise ratios of indium, gallium, aluminum, and nitrogen for the crystal coat, which results in a bluish color.

But on their own, not even cutting-edge LEDs can produce anything appropriate for the living room. The blue- tinted illumination is fine for, say, a pen flashlight on a keychain, but it doesn’t come close to the warm light the human eye desires.

There are two ways LED manufacturers are able to create a pleasant white light, in the 1990s, the preferred technique was to combine red, green, and blue LEDs. But they all have different efficiencies and operational requirements. So now heat movement, power supply, and drivers – the bulbs’ controlling circuit boards – are getting more intricate.

The LEDs found in current home applications are blue diodes covered with a powdered undercoat called a phosphor, which contains rare- elements that filter blue light. The phosphor is commonly yellow, and depending on the structure of the phosphor and the portion of unconverted blue light, the resulting “white” light can range from the warm radiance favored for home use to cooler tints more suited to, say, retail and outdoor use.

Although still rather costly to produce, LEDs are becoming cheaper, just as Haitz’s law predicted, due to both technical developments and economies of scale. They’re also getting brighter, which means retailers can use fewer of them per bulb, further driving down costs. Things are progressing so quickly, in fact, that Haitz, now retired, thinks his law will soon expire. Someday around 2020, he says, bulbs manufactured for our conventional infrastructure will max out, since at some point supplementary brightness from a single socket would be overkill. We’ll reach a time where we can only move forward by manufacturing quantities of luminous flux that nobody needs,” he says. After that, development would continue only if the Edison socket vanished and we left light bulbs altogether – most likely to flat-panel LEDs, Haitz says.