It’s very common that the LED lights will become darker after using for a long time. There are mainly three reasons.
LED chips are required to work at DC low voltage (below 20V), but our usual mains supply is AC high voltage (AC 220V). To turn the mains into the electricity needed for the lamp, you need a device called "LED constant current drive power."
In theory, as long as the parameters of the driver match the lamp bead, the power supply can be continuously used and used normally. The internals of the drive are complicated, and any device (such as capacitors, rectifiers, etc.) may cause a change in the output voltage, which may cause the lamp to become darker.
Drive damage is one of the most common faults in LED luminaires and can usually be resolved after replacing the drive.
The LED itself is composed of one lamp bead. If one or a part of it is not lit, it will inevitably make the whole fixture dark. The lamp beads are generally connected in series and then in parallel - so if a certain lamp bead burns, it may cause a batch of lamp beads to be off.
After burning, the surface of the lamp bead has obvious black spots. Find it, use a wire to connect it to the back of the lamp, short-circuit it, or replace it with a new lamp bead.
It’s a coincidence that the LED burns one at a time. If it burns frequently, consider the drive problem - another manifestation of drive failure is burning the lamp bead.
The so-called light decay is that the brightness of the illuminant is getting lower and lower - this situation is more obvious on incandescent and fluorescent lamps.
LED lights can not avoid light decay, but its light decay rate is relatively slow, it is difficult to see changes with the naked eye. However, it does not rule out inferior LEDs, or inferior light beads, or due to objective factors such as poor heat dissipation, resulting in faster LED light decay.