Illumination device and method for controlling an illumination device over changes in drive current and temperature

摘要

An illumination device and method is provided herein for controlling individual light emitting diodes (LEDs) in an LED illumination device, so that a desired luminous flux and a desired chromaticity of the device can be maintained over changes in drive current and temperature. According to one embodiment, the illumination device comprises a plurality of emission LEDs, a storage medium, an LED driver and receiver circuit and a control circuit. The storage medium may store a table of calibration values correlating forward voltage and drive current to chromaticity and luminous flux at a plurality of temperatures for each of the plurality of emission LEDs. The LED driver and receiver circuit may apply respective drive currents to the emission LEDs to produce substantially continuous illumination, and may periodically turn the emission LEDs off to measure operating forward voltages that develop across each emission LED. The control circuit may determine whether a target luminance setting or a target chromaticity setting for the illumination device has changed, and if so, may determine new respective drive currents needed to achieve the target luminance setting and the target chromaticity setting using the operating forward voltages measured across each emission LED, the table of calibration values and one or more interpolation techniques.

主权项

1. A method for controlling an illumination device comprising a plurality of emission light emitting diodes (LEDs), wherein the method comprises:
applying respective drive currents to the plurality of emission LEDs to drive the plurality of emission LEDs substantially continuously to produce illumination; periodically turning the plurality of emission LEDs off for short durations of time; measuring a forward voltage presently developed across each emission LED by applying a non-operative drive current to each emission LED, one LED at a time, during the short durations of time the plurality of emission LEDs are periodically turned off; and determining chromaticity values that are expected for each emission LED using the forward voltage measured across each emission LED, the respective drive current supplied to each emission LED, a table of stored calibration values correlating forward voltage and drive current to chromaticity at a plurality of different temperatures, and one or more interpolation techniques.