This situation is called "light decay", which is a normal loss phenomenon of LED lamps. There are two main reasons: first, the heat generated by the long-term work of the LED chip accelerates the aging of the chip, leading to a decrease in luminous efficiency; second, the accumulation of dust inside the lamp blocks the light output. High-quality LED lamps have a slow light decay rate, and can still meet daily lighting needs after 5-8 years of normal use. Regular cleaning of lamp dust can slow down light decay.