Color tunable pcLEDs based on temporal saturation of phosphors
Phosphor converted LEDs (pcLEDs) are color tuned by temporal saturation of an electronic transition from which the phosphor emission arises. A single such pcLED is individually color tunable. In an array of such pcLEDs each pixel may be separately color tunable.
1 . A light emitting device comprising:
a semiconductor light emitting diode configured to emit a train of primary light pulses, each primary light pulse having a maximum amplitude and a temporal full width at half maximum, adjacent light pulses in the train separated in time from each other by a temporal pulse spacing;
a phosphor material arranged in an optical path for light emitted by the semiconductor light emitting diode and characterized by having an electronic transition that absorbs primary light emitted by the semiconductor light emitting diode and by emitting secondary light of a longer wavelength in response to absorbing the primary light, the phosphor material electronic transition characterized by a relaxation time; and
a controller configured to drive the semiconductor light emitting diode to emit the train of primary light pulses with their temporal full width at half maximum less than the phosphor material electronic transition relaxation time and with a combination of temporal full width at half maximum and maximum amplitude that saturates the phosphor material electronic transition.
2 . The light emitting device of claim 1 , wherein the light pulse temporal full width at half maximum is less than or equal to 30 nanoseconds, less than or equal to 20 nanoseconds, less than or equal to 10 nanoseconds, or less than or equal to 5 nanoseconds.
3 . The light emitting device of claim 1 , wherein the controller is configured to adjust the temporal full width at half maximum, the maximum amplitude, the temporal pulse spacing, or any combination thereof to adjust an amount of primary light transmitted unabsorbed through the phosphor material.
4 . The light emitting device of claim 1 , wherein:
the light emitting device emits white light characterized by a correlated color temperature; and
the controller is configured to adjust the temporal full width at half maximum, the maximum amplitude, the temporal pulse spacing, or any combination thereof to adjust the correlated color temperature by adjusting an amount of primary light transmitted unabsorbed through the phosphor material.
5 . The light emitting device of claim 1 , wherein:
the light emitting device emits light characterized by a color point x,y in a CIE 1931 chromaticity diagram; and
the controller is configured to adjust the temporal full width at half maximum, the maximum amplitude, the temporal pulse spacing, or any combination thereof to adjust the color point by adjusting an amount of primary light transmitted unabsorbed through the phosphor material.
6 . The light emitting device of claim 1 , wherein the primary light is blue light.
7 . The light emitting device of claim 1 , wherein the phosphor material electronic transition relaxation time is less than or equal to 10 milliseconds.
8 . The light emitting device of claim 7 , wherein the phosphor material electronic transition relaxation time is less than or equal to 1 millisecond.
9 . The light emitting device of claim 8 , wherein the phosphor material electronic transition relaxation time is less than or equal to 0.1 millisecond.
10 . The light emitting device of claim 1 , wherein the phosphor material is or comprises YAG:Ce 3+ .
11 . The light emitting device of claim 1 , wherein the phosphor material is or comprises CASN:Eu 2+ .
12 . The light emitting device of claim 1 , wherein the phosphor material is or comprises KSF:Mn 4+ .
13 . The light emitting device of claim 1 , wherein:
the primary light is blue light;
the phosphor material is YAG:Ce 3+ ; and
the controller is configured to adjust the temporal full width at half maximum, the maximum amplitude, the temporal pulse spacing, or any combination thereof to adjust correlated color temperature between 3950 K and 6070 K.
14 . An illumination system comprising:
a plurality of light emitting devices of claim 1 arranged in an array; and
an optic or optical system arranged to image the array to form an output illumination beam.
15 . The illumination system of claim 14 , wherein at least some of the light emitting devices are independently operable to steer a direction of the output illumination beam.
16 . A display system comprising:
a light source comprising a plurality of the light emitting devices of claim 1 arranged in an array;
a display; and
an optic or optical system arranged to couple light from the light source into the display.
17 . A mobile device comprising:
a camera;
a flash illumination system comprising a light source comprising a plurality of the light emitting devices of claim 1 arranged in an array and an optic or optical system arranged to at least partially collimate light emitted by the light source; and
a controller configured to operate the light emitting devices to match a field of view of the flash illumination system to a field of view of the camera.
18 . A method of operating a light emitting device,
the light emitting device comprising
a semiconductor light emitting diode configured to emit a train of primary light pulses, each primary light pulse having a maximum amplitude and a temporal full width at half maximum amplitude, adjacent light pulses in the train separated in time from each other by a temporal pulse spacing; and
a phosphor material arranged in an optical path for light emitted by the semiconductor light emitting diode and characterized by having an electronic transition that absorbs primary light emitted by the semiconductor light emitting diode and by emitting secondary light of a longer wavelength in response to absorbing the blue light, the phosphor material electronic transition characterized by a relaxation time;
the method comprising driving the semiconductor light emitting diode to emit the train of primary light pulses with their temporal full width at half maximum less than the phosphor material electronic transition relaxation time and with a combination of temporal full width at half maximum, maximum amplitude, temporal pulse spacing, or any combination thereof selected to adjust primary light transmitted unabsorbed through the phosphor material to a desired amount.
19 . The method of claim 18 , wherein the light emitting device emits an output beam of white light characterized by a correlated color temperature, comprising driving the semiconductor light emitting diode to emit the train of primary light pulses with a combination of temporal full width at half maximum, maximum amplitude, temporal pulse spacing, or any combination thereof selected to adjust the correlated color temperature to a desired value.
20 . The method of claim 18 , wherein the light emitting device emits an output beam of light characterized by a color point x,y in a CIE 1931 chromaticity diagram, comprising driving the semiconductor light emitting diode to emit the train of primary light pulses with a combination of temporal full width at half maximum, maximum amplitude, temporal pulse spacing, or any combination thereof selected to adjust the color point to a desired value.