What is light decay? How to reduce light decay and extend the life time of luminary?

1. What is light decay?

Light decay refers to the fact that after a period of lighting, the light intensity of an LED will be lower than the original light intensity, and the lower part is the light decay of the LED.

In recent years, LED technology has advanced significantly. Similar to conventional lighting fixtures, LED lamps also experience light decay, a crucial factor determining their lifespan. For instance, LED street lamps often boast an L70 rating exceeding 100,000 hours. This means that after 100,000 hours of operation, these lamps will emit light at 70% of their initial output. In contrast, traditional lighting fixtures typically have an L70 value of about 10,000 hours, indicating that LED lights degrade much more slowly than their traditional counterparts. Despite this slower decay, the impact on lighting efficiency due to light degradation remains a consideration.

The term "light decay" only indicates the reduction of light value. "Light decay" does not mean that the light value is reduced to zero. Light decay only indicates that the light output of the light source or lamp is less than that of a certain moment before, and it cannot indicate whether the light source or lamp has been physically or chemically damaged. For example, as the use time increases, dust accumulates on the lamp and the light output of the lamp decreases. For another example, when light passes through an optical fiber, light decay will occur as the optical fiber becomes longer. None of these indicate that the light source is damaged, but these systems all experience light decay. Therefore, light decay is neither a synonym for failure nor a synonym for damage. It is wrong to understand light decay as a must for light source damage or failure.

Below is the light decay curve of Cree Company

2. How to reduce light decay?

The light decay of LED is related to its junction temperature. The so-called junction temperature is the temperature of the semiconductor PN junction. The higher the junction temperature, the earlier the light decay occurs, that is, the shorter the life. As can be seen from the figure, if the junction temperature is 105 degrees, the life of the brightness is reduced to 70% for only more than 10,000 hours, 95 degrees for 20,000 hours, and the junction temperature is reduced to 75 degrees, the life is 50,000 hours, and it can be extended to 90,000 hours at 65 degrees. Therefore, the key to prolonging the led street light, LED flood light life is to reduce the LED junction temperature.

3. How to prolong the lifetime of LED fixtures?

When we purchase LED lamps, we must check whether its heat dissipation design is good.