Method and apparatus for providing a passive color control scheme using blue and red emitters

Abstract

A lighting device capable of generating warm or neutral white light using blue light-emitting diodes (“LEDs”), red LEDs, and/or luminescent material that responds to blue LED emission is disclosed. The lighting device includes multiple first solid-state light-emitting structures (“SLSs”), second SLSs, and balancing resistor element. The first SLS such as a string of blue LED dies connected in series is able to convert electrical energy to blue optical light, which is partially turned into longer wavelength emission by the luminescent material. The second SLS such as a red LED die is configured to convert electrical energy to red optical light, wherein the second SLSs are connected in series. While the first SLSs and second SLSs are coupled in parallel, the balancing resistor element provides load balance for current redistribution between the first and second SLSs in response to fluctuation of operating temperature.

What is claimed is: 
     
         1 . A light-emitting device, comprising:
 a string of first light-emitting diodes (“LEDs”) having multiple junctions able to convert electrical energy to optical light having a range of wavelengths from 400 to 500 nanometer (“nm”), wherein the first LEDs are connected in series; and   a string of second LEDs having multiple junctions configured to convert electrical energy to optical light having a range of wavelengths from 580 to 700 nm, wherein the second LEDs are connected in series, wherein the string of first LEDs and the string of second LEDs are coupled in parallel allowing current redistribution in response to temperature fluctuations.   
     
     
         2 . The device of  claim 1 , further comprising a first balancing resistor element coupled to the string of first LEDs for load balance and current redistribution. 
     
     
         3 . The device of  claim 2 , further comprising a second balancing resistor element coupled to the string of second LEDs for load balance and current redistribution. 
     
     
         4 . The device of  claim 1 , further comprising a shunt controller coupled to the string of second LEDs and able to activate at least one shunt red LED to compensate loss of red flux due to temperature variation. 
     
     
         5 . The device of  claim 1 , wherein the string of first LEDs is able to convert electrical energy to blue light. 
     
     
         6 . The device of  claim 5 ,
 wherein blue LEDs have a phosphor layer configured to convert at least a portion of blue photons into photons in yellow or green spectral region; and   wherein the phosphor is deposited in proximity of blue LED chips.   
     
     
         7 . The device of  claim 5 , wherein each blue LED includes a phosphor layer which is located remotely from an LED chip. 
     
     
         8 . The device of  claim 5 , wherein the string of second LEDs is able to convert electrical energy to red light. 
     
     
         9 . The device of  claim 2 , wherein the first balancing resistor element includes a passive resistor having a predefined value based on physical properties of first LEDs and second LEDs. 
     
     
         10 . A solid-state lighting device, comprising:
 a string of first light-emitting diodes (“LEDs”) having multiple junctions able to convert electrical energy to bluish optical light;   a string of second LEDs having multiple junctions configured to convert electrical energy to reddish light; and   a red light flux balancing element coupled to the string of second LEDs in series and capable of redistributing current passing through the string of second LEDs to compensate differential voltage across the string of second LEDs due to fluctuation of junction temperature of the string of second LEDs.   
     
     
         11 . The device of  claim 10 , further comprising a blue light flux balancing element coupled to the string of first LEDs in series and capable of redistributing current passing through the string of first LEDs in response to temperature fluctuation across junction temperature causing differential voltage across the string of first LEDs. 
     
     
         12 . The device of  claim 11 ,
 wherein the blue light flux balancing element is a passive resistor having a predefined value based on physical properties of first LEDs; and   wherein the red light flux balancing element is a passive resistor having a predefined value based on physical properties of second LEDs.   
     
     
         13 . The device of  claim 10 , further comprising a shunt controller coupled to the string of second LEDs and able to activate at least one shunt red LED to compensate loss of red flux due to temperature variation. 
     
     
         14 . The device of  claim 10 , wherein the string of first LEDs is able to convert electrical energy to blue light having a range of wavelengths from 400 nm to 500 nm. 
     
     
         15 . The device of  claim 10 , wherein the string of second LEDs is able to convert electrical energy to red light having a range of wavelengths between 580 nm and 700 nm. 
     
     
         16 . A lighting device, comprising:
 a string of blue light-emitting diodes (“LEDs”) having multiple junctions able to convert electrical energy to blue light, wherein the blue LEDs are connected in series; and   a string of red LEDs having multiple junctions configured to convert electrical energy to red light, wherein the red LEDs are connected in series, wherein the string of blue LEDs and the string of red LEDs are coupled in series; and   a shunt controller coupled to the string of red LEDs and able to activate at least one shunt red LED to compensate loss of red flux in response to temperature fluctuation affecting differential voltage drops across the string of blue LEDs and the string of red LEDs.   
     
     
         17 . The device of  claim 16 , wherein the string of blue LEDs is able to convert electrical energy to blue light having a wavelength range from 400 nm to 500 nm. 
     
     
         18 . The device of  claim 16 ,
 wherein the blue LEDs have a phosphor layer configured to convert at least a portion of the blue photons into photons in yellow or green spectral region; and   wherein the phosphor is deposited in proximity of blue LED chips.   
     
     
         19 . The device of  claim 16 , wherein the string of red LEDs is able to convert electrical energy to red light having a wavelength range between 580 nm and 700 nm. 
     
     
         20 . An illuminating apparatus capable of emitting optical light comprising the device of  claim 16 .