LED只要點亮就會光衰。
節錄一下CREE的XM-L文檔：
Lumen Maintenance Projections
Cree currently recommends a maximum drive current of 2000 mA for XLamp XM-L white in designs seeking the ENERGY STAR* 35,000 hour lifetime rating (≥ 94.1% luminous flux @ 6000 hours)
or 25,000-hour lifetime rating (≥ 91.8% luminous flux @ 6000 hours).
