Patent ID: 8471565
Filing Date: 2013-06-25
Classification: G01R,H05B

Abstract:
1. A method of estimating the output light flux of a light emitting diode, comprising: applying a drive current waveform to the LED over a period of time comprising a testing period; monitoring the forward voltage across (Vf) the LED during the testing period; and estimating the output light flux as a function of changes (ΔVf) in the forward voltage, wherein the drive current waveform comprises a first current portion (I wherein Φ age is the output flux after ageing, Φ pristine is the output flux before ageing, P light age is the power supplied to the LED after ageing which results in light output rather than heating and P light pristine is the power supplied to the LED before ageing which results in light output rather than heating, and wherein P light age is obtained from: wherein P in-age the total input power, P heat pristine is the power supplied to the LED before ageing which results in heating rather than light, ΔV f age is the difference in measured forward voltage before and after the first current portion and after ageing, and ΔV f pristine is the difference in measured forward voltage before and after first current portion and before ageing.