Temperature influence on LED analysis (1)
LED(Light Emitting Diode:As the fourth-generation light source, light-emitting diodes (LEDs) have great potential for development due to their advantages of energy saving, environmental protection, and long life. However, because LEDs are extremely sensitive to temperature, an increase in junction temperature affects the lifetime, light efficiency, light color (wavelength), color temperature, light shape (distribution), and forward voltage, maximum injection current, photometry, color, and electrical properties of the LED. Parameters and reliability. This article analyzes in detail the effect of temperature increase on the photoelectric parameters and reliability of LED, in order to facilitate the design and development of LED chips and LED lighting products.
1. Excessive temperature will cause permanent damage to the LED as well as automotive headlight bulbs.
1)The operating temperature of the LED exceeding the carrying temperature of the chip will rapidly reduce the luminous efficiency of the LED, resulting in significant light failure and causing damage.
2)The LEDs are mostly encapsulated in transparent epoxy. If the junction temperature exceeds the solid phase transition temperature (usually 125°C), the encapsulating material will shift to a rubbery shape and the coefficient of thermal expansion will rise, causing the LED to open and fail.
2.Increased temperature reduces LED lifetime.
1)The lifetime of an LED is reflected in its light decay, that is, the time is long and the brightness becomes lower and lower until it finally extinguishes. Usually defines the LED light flux decay time of 30% of its life.
The cause of LED light decay is usually due to the following aspects:
1) The defects existing in the LED chip material will rapidly proliferate and multiply at a higher temperature until invading the light emitting area, forming a large number of non-radiation recombination centers, and seriously reducing the luminous efficiency of the LED.
In addition, under high-temperature conditions, micro-defects in the material and fast-spreading impurities from the interface and the plate can also be introduced into the light-emitting region to form a large number of deep levels, which will also accelerate the light-failure of the LED device.
2) At high temperatures, the transparent epoxy resin will denature and yellow, affecting its light transmission performance. The higher the operating temperature, the faster the process will proceed. This is another major cause of LED light failure.
3) Phosphor light decay is also a major cause of LED light decay, because the attenuation of phosphors at high temperatures is severe.
Therefore, the high temperature is the main cause of LED failure and shortened LED lifetime.
The light decay of different brands of LED is different, usually LED manufacturers will give a set of standard light decay curve. For example, the luminous decay curve of Luxeon K2 from Lumiled Inc. is shown in Figure 1. When the junction temperature is increased from 115°C to 135°C, the life span will be shortened from 50,000 hours to 20,000 hours.
