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Solid-state light source lightbulb: Light-emitting-diode (LED) bulbs produce more light with less energy than incandescents, could potentially claim a lamp life much longer than 10 years, and, unlike compact fluorescents, are free of mercury. But they have other drawbacks. To obtain that lengthy life, LED devices need to stay relatively cool. And to successfully replace current bulbs, LEDs would need to broadcast their rays widely, yet many currently on the market give off light unidirectionally, like a flashlight.
Nadarajah Narendran, a professor and director of research at the Lighting Research Center at Rensselaer Polytechnic Institute, and his co-inventors came up with an LED bulb that addresses both problems in Patent no. 8,292,468. “Heat is one of the problems with LEDs,” Narendran says. “If you don't create it in the right way, you may not have the long life.” Other LEDs have large metal heat sinks that dissipate heat at the base or back of the bulb. That placement can create a shadow and the flashlight effect, he says. His device inverts the typical design by putting the LED source and the metal heat sink at the front of the bulb, where there is more exposure to surrounding air and cooling is more efficient. The bulb also has interior features that reflect and refract to produce light distribution that mimics an incandescent lamp. The result: a long-lived bulb with familiar aesthetics. “The lighting industry is in the process of a transformation,” Narendran says. “In many cases, the look will not change—it will look like a lightbulb—but what's inside will change.”