"One of the fastest developing lighting technologies today is the light-emitting diode (or LED). A type of solid-state lighting, LEDs use a semiconductor to convert electricity into light, are often small in area (less than 1 square millimeter) and emit light in a specific direction, reducing the need for reflectors and diffusers that can trap light.

"They are also the most efficient lights on the market. Also called luminous efficacy, a light bulb’s efficiency is a measure of emitted light (lumens) divided by power it draws (watts). A bulb that is 100 percent efficient at converting energy into light would have an efficacy of 683 lm/W. To put this in context, a 60- to 100-watt incandescent bulb has an efficacy of 15 lm/W, an equivalent CFL has an efficacy of 73 lm/W, and current LED-based replacement bulbs on the market range from 70-120 lm/W with an average efficacy of 85 lm/W.

"In 1962 while working for General Electric, Nick Holonyak, Jr., invented the first visible-spectrum LED in the form of red diodes. Pale yellow and green diodes were invented next. As companies continued to improve red diodes and their manufacturing, they began appearing as indicator lights and calculator displays in the 1970s. The invention of the blue diode in the 1990s quickly led to the discovery of white LEDs -- researchers simply coated the blue diodes with a phosphor to make it appear white. Shortly thereafter, researchers demonstrated white light using red, green and blue LEDs. These breakthroughs led to LEDs being used in a variety of applications including traffic lights, flashlights and TVs.

"To make LEDs an option for general lighting, researchers next had to focus on improving the efficiency of LEDs -- which in the beginning were no more efficient than incandescent bulbs. In 2000, the Energy Department partnered with private industry to push white LED technology forward by creating a high-efficiency device that packaged LEDs together.

"When the Department announced the L Prize competition in 2008 (a competition designed to spur the development of ultra-efficient solid-state lighting products to replace common lighting technologies), there were just a few LED bulbs on the market that could serve as a replacement for incandescents, and most were 25-40 watt equivalents. In late 2009, Philips Lighting North America entered its LED bulb in the L Prize 60-watt replacement category. (Why focus on this type of bulb? In 2010, the Department estimated there were approximately 971 million 60-watt incandescent bulbs in use.) After a rigorous evaluation process, including testing by independent laboratories and field assessments, the Energy Department announced that Philips Lighting North America won the first L Prize in 2011. The ability to hit the tough L Prize performance targets showed it could be done and drove others in the market to strive higher.

"Lighting companies continued to make improvements to both the quality of light and the energy efficiency of LEDs while cutting their costs. Since 2008, the cost of LED bulbs has fallen more than 85 percent, and most recently, a number of retailers announced that they will sell LEDs at $10 or less. Today’s LED bulbs are also six to seven times more energy efficient than conventional incandescent lights, cut energy use by more than 80 percent and can last more than 25 times longer. Taken together, these advancements have led to rapid deployment in the past of couple years in both commercial and residential applications. In 2012 alone, more than 49 million LEDs were installed in the U.S. -- saving about $675 million in annual energy costs -- and as prices continue to drop, LEDs are expected to become a common feature in homes across the country.

"Incandescents and existing lighting fixtures use designs that date back to Edison’s days. Replacing the old bulbs with LEDs is only the tip of the iceberg when it comes to saving energy on lighting. LED lighting systems designed to take full advantage of LED’s strengths have even greater energy-savings potential than forcing LEDs into 19th century fixtures.

It’s hard to tell where lighting technology will go in the future, but one thing is clear: it won’t be your grandfather’s light bulb."

- from ENERGY.GOV "The History of the Light Bulb http://energy.gov/articles/history-light-bulb