Why do led strips get darker and darker over time?

Many people have such a life experience--the led strip that just bought back is very bright, but after a period of time, the light will be more and more dark. Why is this?

The longer the strip is used, the lower the brightness, because the LED will have the phenomenon of light decay. What is light decay?

It refers to for the lamp, after a period of use, its brightness will gradually reduce, and can not be recovered, the lower part is called LED light failure.

Light decay generally refers to the light flux of the luminaire. 
 

When charging the surface of the photosensitive drum, with the accumulation of charge on the surface of the photosensitive drum, the potential also increases continuously, and finally reaches the saturation potential, that is, the highest potential.
 

The surface potential will decrease with the passage of time, and the general working potential is slightly lower. This process of natural decrease of potential over time is called "dark decay". When the photosensitive drum is exposed by scanning, the potential of the dark area (refers to the surface of the photoconductor where the light is not irradiated) is still in the process of fading. 

The inner carrier density in the bright area (refers to the surface of the photoconductor where the light is irradiated) increases rapidly, so does the electrical conductivity, forming the photoconductive voltage. The charge quickly disappears, the potential of the photoconductive surface also decreases rapidly, and finally slows down, which is called "light decay".

Usually, the manufacturer of LED bead capsulation is in the laboratory conditions (25℃ room temperature), with 20mA DC current continuously lit led bead for 1000 hours, and then its brightness and the initial brightness is compared.

The formula for calculating light decay is: the decay of N hours = 1 - (the luminous flux of after N hours / the initial luminous flux)

Different manufacturers of led strips, the light decay is different. Generally, the light decay of high power LED strip is higher. This is directly related to the temperature generated during the use of the led strip, and also affected by chip, phosphor, capsulation technology and so on.