What kind of concept is the life of LED? What is a bathtub curve?
"Life" is the survival time of things from birth to death. For electronic components, its "life" refers to the duration of its internal physical mechanism from formation to disappearance. LED is an electrical-optical conversion. The physical function of photons generated by the energy band transition of electron-hole pairs is theoretically an infinitely long process, and it is a long-life "Yong J" brand, but any material, even the semiconductor material that constitutes LED, Including its electrodes and other materials, under long-term electrical and thermal loading, it will eventually decay, age, and eventually lose its original function, resulting in "death" - failure. Therefore, although the LED is solid-state light, it also has its lifetime. Generally speaking, this device, like other semiconductor devices, has a very long "life" in theory. The so-called life of LED and the life of practical LED devices (referring to LED Lamp) are two concepts. Like other electronic components, it must follow the general law of things from birth to death - "bathtub curve". Figure 94-1 shows the laws of death (or failure) of objects and time in nature.
As can be seen from the figure, this curve can be divided into three periods:
(1) t0 -t1 period
This is a period of time in the early days of the device's life, it initially exhibits a high failure rate, and as time increases
When the failure rate is long, the failure rate gradually decreases to t1, and the failure rate remains at a relatively low level, which is called the early failure period from t0 to t1. Take people as an example. From birth to adolescence, infants have a higher mortality rate than young and middle-aged infants due to congenital deficiencies, insufficient resistance and immunity. Similarly for LEDs, due to the defects formed in the manufacturing process of the device and the factors such as missed detection and detection, some "inherently deficient" devices are "mixed out" to the user, and once used, they will be exposed, resulting in a high failure rate in the initial use.
(2) t1-t2 period
This period of time is often very long and is the so-called "life period", which refers to this period of time, due to "congenital deficiencies"
Or devices with poor quality control are exposed during the t0-t1 period, so for the most part "normal" devices can work reliably and perform their mission. Of course, there will also be a very low rate of device failure, just as people will die due to sudden causes in young adulthood. This kind of failure is very random, so this period is called the random failure period.
(3) ≥t2 period
This is due to various fatigue factors such as weathering, aging, and natural wear after the device has been working for a long time.
In the aging period, the function is gradually lost, and the failure rate increases rapidly. Therefore, this period is also called the fatigue failure period. The failure rate of devices entering this period increases linearly.
Obviously, the bathtub curve applies to all kinds of objects including LEDs. For different objects, their own definition of "failure" needs to be defined, such as death for humans and animals, and another definition for electronic components such as LEDs.
Note that the above description is for the totality of objects, not for a single object. In fact, this is a statistical concept. Therefore, "lifetime" is also a statistical average and cannot be estimated by a single unit. For example, when we say that the average life expectancy of a person is 80 years old, we refer to a group of people within a certain range. A certain person in this group may live to be 100 years old, or may die at the age of three. The lifespan of a population cannot be "assessed" by the lifespan of a single individual. The same is true for LEDs, and the so-called 100,000 hours and 50,000 hours as a whole cannot be used as a product to test a certain or a certain batch of LEDs. Generally speaking, "lifetime" cannot be used as a parameter to detect whether the LED is qualified or not, and the reason is also here.
