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Typical indicator LEDs are designed to operate with no more than 30–60 mW of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt [W]. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.
One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit power input. White LEDs quickly met and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made 5W LEDs available with a luminous efficacy of 18–22 lumens per watt [lm/W]. For comparison, a conventional 60–100 W incandescent light bulb produces around 15 lm/W, and standard fluorescent lights produce up to 100 lm/W. A recurring problem is that efficiency will fall dramatically for increased current. This effect is known as droop and effectively limits the light output of a given LED, increasing heating more than light output for increased current.
As of September 2009, some HPLEDs manufactured by Cree Inc. now exceed 105 lm/W.
On November 19, 2008 Cree issued a press release about a laboratory prototype LED achieving 161 lm/W at room temperature. The total output was 173 lumens, and the correlated color temperature was reported to be 4689 K. |
