Method and apparatus for providing a passive color control scheme using blue and red emitters
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.
1. A solid-state lighting device comprising:
a string of first light-emitting diodes (“LEDs”) having multiple junctions configured to convert electrical energy to bluish optical light;
a string of second LEDs having multiple junctions configured to convert electrical energy to reddish light, wherein a first end of the string of second LEDs is coupled to the string of first LED in series; and
a red light flux balancing element coupled in series to the string of second LEDs, the red light flux balancing element comprising a shunt controller in parallel with at least one shunt red LED, the shunt controller configured to redistribute current passing through the at least one shunt red LED in response to fluctuation of junction temperature of the string of second LEDs and to detect loss of red flux in response to temperature fluctuation.
2. The device of claim 1 , wherein the shunt controller is a passive resistor having a predefined value based on physical properties of second LEDs.
3. The device of claim 1 , 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.
4. The device of claim 1 , 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.
5. The device of claim 1 , wherein the red light flux balancing element is coupled to a second end of the string of second LEDs, the second end being different from the first end of the string of second LEDs.