At present, white LED lamps have very serious light attenuation problems, especially for low power white LED Street lights. Light attenuation phenomenon dramatically reduces the working life for them. Generally, white LED lamps are very expensive in LED lighting market. If manufacturers want to stay in business, they have to increase the working life of their products. But they cannot. There are several causes for the problem: the degeneration of fluorescent powder in high temperatures; the degeneration of blue-ray LEDs; the degeneration of LED bases; other packaging materials; packaging technique; misuse (improper power supply, bad cooling). In below, we will discuss them separately in more details.
The degeneration of fluorescent powder in high temperatures:
The stimulated light efficiency of fluorescent powder will drop with the increase of temperature. A testing report from a fluorescent powder factory in Guangzhou shows that the stimulated light efficiency of fluorescent powder drops by 2% under 80 oC. However, this is just a short-term experiment. When temperatures drop back to the normal level, fluorescent powder regains the original performance. If we intend to find whether this degeneration is restorable or not after long-term work, aging tests are necessary.
In some cases, we will find that after a period of aging tests (1000 hours for lower power white LEDs, 2000 hours for high power white LED Street Light), white LED lamps become brighter. This situation may cause by following reasons:
- Fluorescent powder used together with epoxy glue lead to the degeneration of fluorescent powder. In the initial effect of temperatures, the stimulated lighting emitting ability of fluorescent powder will be recovered to some degrees.
- In some cases, the stimulated lighting emitting ability of fluorescent powder will be raised rather than dropped for being combined with epoxy glue.
- The performance of blue-ray LED chips will be enhanced after a period of work.
Among the aging tests of low power LED white lamps, scientists found that the luminous flux of them will increase within 200 hours’ continuous work. But after 200 hours, situations are completely different. They will inevitably meet with light attenuation problems. Conditions are a little bit of better for high power white LED lights. The luminous flux of these lamps will become unstable within the working range from 100 hours to 6000 hours. However, after 6000 hours work, they will also meet with attenuation problems.