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Difference between revisions of "LED"
new section about driving and overdriving the LED
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[http://www.candlepowerforums.com/vb/showthread.php?t=270419 CPF Post] with pictures of common flashlight LED's | [http://www.candlepowerforums.com/vb/showthread.php?t=270419 CPF Post] with pictures of common flashlight LED's | ||
==Driving the LED== | |||
As the available voltage to a LED increases, the current (in amps or milliamps) drawn by the LED increases. LED's are usually more efficient at lower voltages and currents, but get brighter as more power (power being volts times amps and measured in watts) is applied. LED's are evaluated at different currents and a forward voltage (or [[Terminology#Vf|Vf]]) is measured as the voltage drop across the LED at a particular current level, 350mA or 700mA being pretty common benchmarks. In flashlights, an electronic [[driver]] is there to regulate the amount of power delivered to the LED either by controlling the voltage and/or current to the LED. | |||
As more power is applied, more waste heat is generated and must be carried off. At some point a LED will be overdriven which will shorten its life from the tens of thousands of hours a properly driven LED should last. As the LED is overdriven the yellow phosphor on the LED starts to burn and "angry blue" light is emitted. If the light is turned off quickly, the LED may avoid permanent damage, but otherwise the LED will literally burn with brown spots on the LED. Generally when that happens, the maximum output will now be significantly lower. | |||
==LED's in Flashlights== | ==LED's in Flashlights== | ||
Early LED's did not give off that much light, but they were efficient and they would last many thousands of hours before burning out. As they got brighter, they started making their way into flashlights. The classic LED's were 5mm in diameter encased in clear epoxy resin with a round head. As the LED inside gave off light, the rays were shaped by the round head to go straight ahead. Many keychain flashlights use a simple LED like that. These are usually named as 3 mm or 5 mm LED's. The Fenix E01 uses a 5mm Nichia LED. To get additional brightness, some flashlights would combine multiple LED's in the head of the flashlight and maybe include some kind of reflector to shape the light. | Early LED's did not give off that much light, but they were efficient and they would last many thousands of hours before burning out. As they got brighter, they started making their way into flashlights. The classic LED's were 5mm in diameter encased in clear epoxy resin with a round head. As the LED inside gave off light, the rays were shaped by the round head to go straight ahead. Many keychain flashlights use a simple LED like that. These are usually named as 3 mm or 5 mm LED's. The [[Fenix]] E01 uses a 5mm Nichia LED. To get additional brightness, some flashlights would combine multiple LED's in the head of the flashlight and maybe include some kind of reflector to shape the light. | ||
[[File:sscp7led.jpg|thumb|Seoul Semiconductor P7 multi-die LED]]High power LED's were developed to handle higher currents and produce brighter light. They lost the clear plastic shell and had to be mounted to a metal base to draw heat away from the LED before it could burn itself out. Lumileds Luxeon I was a 1-watt LED producing 30 to 60 lumens and was followed by the 3-watt Luxeon III (60-90 lumens, requiring more power than the Luxeon I). They also produced the K2 which could be driven at even higher currents for more output. | [[File:sscp7led.jpg|thumb|Seoul Semiconductor P7 multi-die LED]]High power LED's were developed to handle higher currents and produce brighter light. They lost the clear plastic shell and had to be mounted to a metal base to draw heat away from the LED before it could burn itself out. Lumileds Luxeon I was a 1-watt LED producing 30 to 60 lumens and was followed by the 3-watt Luxeon III (60-90 lumens, requiring more power than the Luxeon I). They also produced the K2 which could be driven at even higher currents for more output. | ||