Power Led
Thursday, November 19th, 2009
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60 LED Blue Solar Power Outdoor Garden String Lights
$1.48 |
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2 X Super WHITE HIGH POWER LED BULBS 1895 53 57 BA9s US
$1.00 |
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1,Led Power Source Test Box/Case Tester w 9V Battery,TB
$0.99 |
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5050 SMD 300 LEDs Strip Light 5M WARM WHITE + 12V Power
$96.00 |
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2pcs 10W White Hi-brightness 600LM Save Power LED NEW
$9.59 |
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1,Led Power Source Test Box/Case Tester w 9V Battery,TB
$0.99 |
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1 PCS 10W Power White LED Light Bulb 500lm 140 Degree
$9.99 |
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new LED lights power Gyro Wrist strength Exercise Ball
$1.25 |
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20 PC 1W StrawHat 8mm 140° High Power White LED 220Kmcd
$28.00 |
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2003-2007 SCION XB K6 LED POWER MIRRORS 2004 2005 2006
$46.95 |
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194/168 White High-Power LED Lights Bulbs Running/Wedge
$11.98 |
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4-port USB 2 HUB 2,000mA AC Power Supply LED Windows 7
$22.95 |
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Universal Travel Adapter AC Power LED USB Port US UK EU
$1.33 |
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Solar Power Car Vehicle LED Warning Security Light
$4.00 |
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50 PC 0.5W StrawHat 8mm 140° High Power Red LED 90Kmcd
$30.99 |
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WHITE 20W LED 1500 LM LUMEN ENERGY SAVING POWER LAMP
$25.99 |
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4pcs 194 168 W5W 1W White High Power LED Lights Bulb
$10.99 |
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Ultra Bright High-Power Aluminum LED Flashlight Torch
$9.80 |
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~4pcs 194 168 W5W 1W White High Power LED Lights Bulbs
$10.99 |
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New 32 LED High Power Strobe (White) Flash Light J48H
$9.99 |
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1x High Quality 30W White 1800 Lumen Save Power LED F
$18.88 |
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30p HIGH POWER 1W 10mm WHITE LED LAMP 360Kmcd FREE SHIP
$36.99 |
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NEW 1PC High-power 20W Warm White LED 1000Lm 14V F
$17.88 |
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95 96 NISSAN 240SX S14 POWER K6 SMOKE SIDE MIRRORS LED
$19.95 |
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Red LED Volt Meter DC 8V-30V Doesn't Require A Power
$11.99 |
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1x LED Driver power supply transformer 20mA 220VAC
$9.99 |
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Red LED Volt Meter DC 7V-30V Doesn't Require A Power
$8.99 |
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High Power 16 LED Strobe (Amber/White) 1W Flash Light
$19.99 |
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5M SMD 5050 RGB LED Strip + Controller + Power Supply
$57.00 |
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4x 194 168 5-SMD White High Power LED Car Lights Bulbs
$14.99 |
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GFS78 2X CCTV 48 LED IR ILLUMINATOR FOR CAMERA W/POWER
$42.99 |
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New 32 LED High Power Strobe (Amber) Flash Light AA32
$14.99 |
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LED POWER LIGHT Red Beam Laser Pointer Pen POWERFUL New
$9.99 |
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T10 WEDGE BULB 2 PCS HIGH POWER BLUE LED 168 L-1051
$1.99 |
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Power 21 LED White Light Lamp Bulb 110V 220V E27 1.4W
$0.10 |
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03 04 05 06 NISSAN 350Z POWER K6 SMOKE SIDE MIRRORS LED
$24.97 |
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1994-2001 CHEVY S10 K6 LED POWER MIRRORS 1998 1999 2000
$44.99 |
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MINI Solar Power Recharge 3 LED Flashlight Keychain
$1.10 |
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MINI Solar Power Recharge 3 LED Flashlight Keychain
$0.01 |
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1992 1993 1994 1995 MAZDA MX3 MX-3 K6 LED POWER MIRRORS
$46.95 |
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Mini Solar Power rechargeble 3 LED Flashlight Keychain
$1.04 |
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03 04 05 06 TOYOTA MATRIX POWER K6 SMOKE MIRRORS LED
$24.97 |
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30p HIGH POWER 1W 10mm WHITE LED LAMP 360Kmcd FREE SHIP
$33.29 |
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97-00 MITSUBISHI MIRAGE POWER K6 SMOKE MIRRORS LED 98
$24.97 |
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2.6W E27 42 LED High Power White Light Bulb 220V
$7.99 |
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New 4x 4 High Power LED Strobe (Amber) 1W Flash Light
$14.99 |
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3*1W 330mA LED Driver Power 12V AC In Constant Current
$0.99 |
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NEW 2x 8 High Power LED Emergency Strobe Light 4R4B
$19.99 |
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30P 10mm HIGH POWER 0.5W BLUE LED LAMP 150Kmcd F/SHIP
$17.19 |
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12V 3 White LED High Power Car Vehicle Auto Lamp Light
$21.20 |
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WHITE LED LICENSE PLATE LIGHTS ACURA TSX RSX RDX RL
$12.99 |
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93-97 NISSAN ALTIMA G2 POWER MIRRORS LED LIGHT 94 95 96
$22.99 |
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New High Power 140 LED Strobe (Amber) Flash Light JAED
$14.99 |
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Hydro Power Desk Clock Blue LED Digital Vintage Gift BN
$0.99 |
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1,Prolight Power 1W Full Color 70 Lumen LM Blue Led,B1
$4.99 |
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Hydro Power Desk Clock Red LED Digital LCD Vintage Gift
$0.99 |
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BA9S BULB 2 PCS SMD HIGH POWER BLUE LED LIGHT L-1105
$1.99 |
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Wrist Ball Gyro Power Exercise Gadget 4 LED Lights Red
$0.99 |
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92-98 BMW E36 4DR K6 SMOKE POWER M3 MIRRORS LED 318 325
$24.97 |
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Solar power LED Pathway Lights FREE SHIPPING adtl items
$11.00 |
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New 4x 4 High Power LED 1W Emergency Strobe Light 2R2B
$17.99 |
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12PCS E27 2W 36 LED High Power Bulb Light Cool White110
$69.99 |
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T10 BULBS 2 PCS SMT SMD 25 LED HID WHITE POWER L-1042
$7.10 |
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30p 10mm HIGH POWER 0.5W RED LED LIGHT 150KmcdFREE SHIP
$17.19 |
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1988-1998 CHEVY GMC C10 C/K PICKUP K6 LED POWER MIRRORS
$47.42 |
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50 PC 0.5W StrawHat 8mm 140° Hi-Power Blue LED 70Kmcd
$31.00 |
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9W=85W E27 High Power LED Bulb Light Spotlight Lamp L11
$36.73 |
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Blue LED Volt Meter DC 7V-30V Doesn´t Require A Power
$10.99 |
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High Power 24 LED White Light Bulb 1.5W E27 110V / 220V
$7.99 |
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LED 4-1 MOON EFFECT HIGH POWER DJ LIGHTING EFFECT LIGHT
$159.99 |
High power LEDs are commonly known as power-saving lights that come with power ratings in the range of 500mW to 10 Watts. They are based on technology meant to increase their luminescent efficiency and therefore can be used almost everywhere from car headlights to high-power lamps. They can be characterized on the basis of a few parameters, such as forward voltage, wavelength, luminous intensity and type.
The wavelength is measured in nanometers and is different for all three basic colors – red, blue and green. By setting these colors to different wavelengths we can get a whole range of exciting colors, also called rainbow colors. This is one of the electro-optical characteristics of an LED. Another important variation is the peak wavelength which suffers the lowest loss due to heat.
Every LED has two kinds of voltages – forward and reverse. A light emitting diode can be made to act like a variable resistor or a capacitor by interchanging reverse and forward voltages. Usually the reverse inclusion is the one with the higher voltage – up to 5V.
Some other vital parameters of high power LEDs are axial intensity and luminous flux. Luminous flux is also known as luminous power and it gives the measurement of the perceived power of light. The power is different at different wavelengths and luminous flux is calculated by adding up power ratings at all wavelengths. This is not the actual power measurement; instead it is the measure of the ‘useful’ power of an LED. Power dissipation is the amount of power consumed by the LED. It is also referred to as the energy lost in the form of heat. Another important characteristic is the emitted color. This color is what we see when the LED is switched on. It can be red, yellow, green, blue or white.
One of the most important concerns regarding the design of high power LEDs is the amount of heat produced due to increased efficiency. High temperatures are not suitable for proper LED operation. They serve to decrease its life and make it less efficient. Thermal management in these LEDs is therefore a major concern in order to make them more productive and longer lasting. There is a critical temperature defined for every LED beyond which it is permanently destroyed. The temperature of an LED keeps on changing with the passage of time and therefore it’s important to maintain a chart to record different temperature ratings against time.
There are three ways by which heat can be discharged: conduction, convection and radiation. Traditional incandescent tungsten light bulbs radiate energy in the form of heat. LEDs, on the other hand, conduct heat from one part to another which takes a long time to be released to the atmosphere. The heat sink should be made by using a material which has high thermal conductivity. Aluminum and copper are two of the most widely used heat sink materials.
Radiation takes less time than conduction and therefore tungsten bulbs do not heat up very quickly. When designing high power LEDs, proper heat conduction is a main issue to be addressed.
The temperature of an LED is directly related to its color. White light is produced by combining base colors in their highest values and therefore the temperature is also the highest in case of white light. Some mechanism is required to keep the color constant when temperature changes due to conduction. A color sensor can be used for this purpose.
Wavelength, forward voltage and luminosity are also affected by the junction temperature of the diode and therefore they also have to be optimal in order to make the LED perform well.
Positive feedback or “thermal runaway” is another problem related to high temperature of the LED. This is a condition in which increased temperature causes the above-mentioned parameters to change unexpectedly resulting in a further increase in temperature. This situation can be critical to the operation of an LED and has to be prevented. It happens when the LED is directed to consume more power in order to produce the desired color. As a result, more heat is produced which raises the temperature and hence the effect.
Thermal runaway is more pronounced when increased junction temperature decreases the luminous intensity and as a result the color sensor reports there is not enough light. This negative cycle goes on and on until the critical temperature is reached and the LED is destroyed. Thermal sensors can be used to correct this problem which constantly measure the junction temperature and make the system shut down if there is an alarming condition.
However, usually this mechanism is not advisable in these LEDs because it makes them useless and obliterates their purpose. Other methods like using natural graphite to spread heat are more practical and useful. This material conducts a large portion of heat dissipated by the LED and as a result releases it to the atmosphere more quickly.
In conclusion, the most important thing to consider in a high power LED design is the selection of appropriate materials that are not affected by the unexpected rise in temperature. This is to ensure that the LED works at all times without shutting down because of the failure of one of its components. Efficient thermal management can increase the critical temperature of an LED and as a result its reliability and longevity is also enhanced. These design decisions on the part of manufacturer help the customer save money and make the most out of these powerful and efficient high power LEDs.
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Article Source: ArticlesBase.com – Thermal Characteristics of High Power Leds