Led-based illumination module on-board diagnostics

Abstract

A light emitting diode (LED) based illumination module performs on-board diagnostics. For example, diagnostics may include estimating elapsed lifetime, degradation of phosphor, thermal failure, failure of LEDs, or LED current adjustment based on measured flux or temperature. The elapsed lifetime may be estimated by scaling accumulated elapsed time of operation by an acceleration factor derived from actual operating conditions, such as temperature, current and relative humidity. The degradation of phosphor may be estimated based on a measured response of the phosphor to pulsed light from the LEDs. A thermal failure may be diagnosed using a transient response of the module from a start up condition. The failure of LEDs may be diagnosed based on measured forward voltage. The current for LEDs may adjusted using measured flux values and current values and a desired ratio of flux values. Additionally, the LED current may be scaled based on a measured temperature.

What is claimed is: 
     
         1 . A method comprising:
 measuring a transient response of an LED based illumination module to illuminating the module from a start up condition; and   estimating a thermal failure of the module based on the measured transient response before an actual thermal failure occurs.   
     
     
         2 . The method of  claim 1 , wherein the measured transient response is taken from the group consisting of a temperature of the module and an output flux of the module. 
     
     
         3 . The method of  claim 1 , wherein the measuring and the estimating are performed by the LED based illumination module. 
     
     
         4 . The method of  claim 1 , wherein the measuring involves a temperature sensor mounted within a light mixing cavity of the module. 
     
     
         5 . The method of  claim 1 , wherein the measuring involves a flux sensor mounted within view of an output window of the module. 
     
     
         6 . The method of  claim 1 , wherein the estimating involves a processor of the module. 
     
     
         7 . The method of  claim 1 , wherein the measuring involves measuring a temperature of the module a period of time after illuminating the module. 
     
     
         8 . The method of  claim 7 , wherein the period of time is greater than one second. 
     
     
         9 . The method of  claim 1 , wherein the estimating involves comparing the measured transient response with a predetermined threshold value. 
     
     
         10 . The method of  claim 1 , further comprising:
 communicating an alarm if the estimating indicates a thermal failure.   
     
     
         11 . The method of  claim 1 , further comprising:
 shutting down the LED based illumination module if the estimating indicates a thermal failure.   
     
     
         12 . A method comprising:
 measuring a first flux intensity value of an LED based illumination module illuminated by a first LED driven with a first current value, wherein the first LED emits light with a first color characteristic;   measuring a second flux intensity value of the LED based illumination module illuminated by a second LED driven with a second current value, wherein the second LED emits light with a second color characteristic;   determining, a third current value based on the first flux intensity value and the first current value; and   determining a fourth current value based on the second flux intensity value, the second current value, and a predetermined ratio of flux intensity of the first LED to flux intensity of the second LED.   
     
     
         13 . The method of  claim 12 , wherein the first LED is driven by the third current value, and wherein the second LED is driven by the fourth current value. 
     
     
         14 . The method of  claim 12 , wherein the first LED and the second LED are mounted to a mounting board, and wherein the measuring of the first and second flux intensity values involves a flux sensor mounted to the mounting board. 
     
     
         15 . The method of  claim 12 , wherein the determining of the third and fourth current values involves a processor of the LED based illumination module.