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The influence of the temperature on the LED

  Date:2013-04-06  Hits:72

LED (Light EmittingDiode: light emitting diode) as the fourth-generation LED light source, very promising because of its energy-saving, environmental protection, long life and other advantages. Because the LED is extremely sensitive to temperature, the junction temperature rise will affect the life of the LED, luminous efficiency, light color (wavelength), color temperature, light shaped (with light) and forward voltage, maximum injection current, brightness, chroma, electrical parameters and reliability. In this paper, a detailed analysis of elevated temperature on the LED optical parameters and reliability, in order to facilitate the design and development of LED chips and LED lighting products.


First, the temperature is too high interested in LED cause permanent damage


(1) LED working temperature over the chip carrier temperature will make the LED luminous efficiency declined rapidly produce significant light decay and cause damage;


(2) LED and more transparent epoxy encapsulated, if the junction temperature exceeds the solid phase transition temperature (typically 125 ° C), the packaging materials to the rubber-like transition and thermal expansion coefficient swells, resulting in an open LED and failure.


Second, the elevated temperature will shorten the lifetime of the LED


LED life performance for its light fades, is a long time, the brightness of getting lower and lower, until finally extinguished. Usually defined LED luminous flux attenuation 30% of the time its life.


LED light failure is usually caused by the following reasons:


(1) at higher temperatures, the LED chip material that defects in rapid proliferation, reproduction, until the light-emitting region is invasive, forming a large number of non-radiative recombination centers, severely reducing the LED luminous efficiency. Further, under high temperature conditions, the material within the micro-defects and the rapid expansion impurities from the interface with the plate will be introduced to the light emitting zone, the formation of a large number of deep levels, will also accelerate the LED device light fades.


(2) high temperature transparent epoxy resin denatured, yellow, affect the light level, the higher the operating temperature this process faster, LED light failure and a major cause.


(3) phosphor light fades also affect a major cause of the LED light failure, because the phosphor attenuation at high temperatures is very serious.


Therefore, the main source of high temperature is caused by the LED light failure, shorten the LED life.


Different brands of LED light decline is different, usually LED manufacturers will be given a standard set of light decay curve. When the junction temperature from 115 ° C to 135 ° C, its life will be reduced from 50,000 hours to 20,000 hours.


Third, the elevated temperature will reduce the light emitting efficiency of the LED


Temperature affect the LED luminous efficiency reasons include the following aspects:


(1) temperature, the concentration of electrons and holes will increase the band gap decreases, the electron mobility will be reduced.

(2) the temperature increases, the chance to reduce the radiative recombination of electrons and holes in the potential well, resulting in non-radiative recombination (generating heat), thereby reducing the internal quantum efficiency of the LED.

(3) The elevated temperature causes the chip blue crest to the long direction of the offset, so that the emission wavelength and excitation wavelength of the phosphor of the chip does not match, can also cause the decrease in white LED external light extraction efficiency.

(4) As the temperature rises, the quantum efficiency of phosphor is reduced, a light decrease, reduce external light extraction efficiency of the LED.

(5) Silicone performance affected by ambient temperature. As the temperature increases, the the silica internal heat stress increase, resulting in lower refractive index of the silica, thus affecting the LED luminous efficiency.

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