Spectral Shift Control for Dimmable AC LED Lighting

Abstract

Apparatus and associated methods involve operation of an LED light engine in which a relative intensities of selected wavelengths shift as a function of electrical excitation. In an illustrative example, current may be selectively and automatically diverted substantially away from at least one of a number of LEDs arranged in a series circuit until the current or its associated periodic excitation voltage reaches a predetermined threshold level. The diversion current may be smoothly reduced in transition as the excitation current or voltage rises substantially above the predetermined threshold level. A color temperature of the light output may be substantially changed as a predetermined function of the excitation voltage. For example, some embodiments may substantially increase or decrease a color temperature output by a solid state light engine in response to dimming the AC voltage excitation (e.g., by phase-cutting or amplitude modulation).

What is claimed: 
     
         1 . A light engine comprising:
 a pair of input terminals adapted to receive a periodic excitation voltage and receive a current, said current flowing in response to the excitation voltage;   a dimmer module having a dimmer control setting and receiving and modifying the current;   a first network in the load wherein the first network includes a first plurality of light emitting diodes (LEDs) arranged in series connection to form a first current path, the first plurality of LEDs having a first color characteristic;   a second network in the load wherein the second network includes a second plurality of light emitting diodes (LEDs) arranged in series connection to form a second current path, the second plurality of LEDs having a second color characteristic;   a transistor that selectively diverts modified current away from at least one of the first and second networks of LEDs; and   wherein the dimmer control setting determines the first and second color characteristics.   
     
     
         2 . The light engine of  claim 1  wherein below a first threshold condition of the dimmer control setting light output of the first plurality of LEDs increases as the dimmer control setting increases while the second plurality of LEDs are bypassed. 
     
     
         3 . The light engine of  claim 2  wherein when the dimmer control setting reaches a point of sufficient excitation to meet the first threshold condition light output of the second plurality of LEDs is allowed. 
     
     
         4 . The light engine of  claim 3  wherein above the first threshold condition of the dimmer control setting light output of the second plurality of LEDs increases as the dimmer control settings increase. 
     
     
         5 . The light engine of  claim 4  wherein the light output of the second plurality of LEDs increases until a second threshold condition is met. 
     
     
         6 . The light engine of  claim 1  wherein the first plurality of LEDs have a color temperature of approximately 3500 K. 
     
     
         7 . The light engine of  claim 6  wherein the second plurality of LEDs have a color temperature of approximately 7000 K. 
     
     
         8 . The light engine of  claim 1  wherein the first transistor is a metal oxide semiconductor field effect transistor (MOSFET). 
     
     
         9 . The light engine of  claim 1  wherein the first plurality of LEDs have a first color and the second plurality of LEDs have a different color that yield a composite color output. 
     
     
         10 . The light engine of  claim 1  wherein when dimming with the dimmer module different wavelengths of light decrease in intensity of the light at variable rates during the dimming process. 
     
     
         11 . The light engine of  claim 1  wherein the first plurality of LEDs are blue LEDs. 
     
     
         12 . The light engine of  claim 11  wherein the second plurality of LEDs are red LEDs. 
     
     
         13 . The light engine of  claim 1  further comprising a rectifier comprising a plurality of LEDs and receiving the modified current of the dimmer module. 
     
     
         14 . The light engine of  claim 1  wherein the plurality of LEDs of the rectifier have a third color characteristic. 
     
     
         15 . The light engine of  claim 1  wherein the plurality of LEDs of the rectifier are blue LEDs.