Display calibration systems and related methods
Display calibration systems and related methods are disclosed that use photo-sensitivity of LEDs to correct for variations between LEDs during initial production and over lifetime for display systems. The display devices include arrays of LEDs and use photo-sensitivity of the LEDs to correct for variations between LEDs. Such LED arrays can produce images directly as in LED billboards and sports arena scoreboards, and smaller Organic LED (OLED) displays, or can produce the backlight for LCD screens for instance. Variations in LED brightness and color can be compensated for in order for such a display to have uniform color and brightness. This compensation is performed in the embodiments disclosed by measuring the signal induced on each LED by uniform incident light as a measurement of the photo-sensitivity of the LEDs.
1. A display device, comprising:
an array of LEDs configured to produce light for the display device;
a memory configured to store correction coefficients, which are associated with the array of LEDs and used to compensate for variations in the light produced by the array of LEDs;
sense circuitry configured for measuring a photo-sensitivity of an LED within the array of LEDs by measuring an open circuit voltage and a short circuit current induced across the LED when the LED is illuminated with a light source; and
control circuitry configured to adjust output power from the LED by:
comparing the measured short circuit current with a short circuit current measurement previously determined while illuminating the LED with the light source to provide an indication of a variation in intensity of light produced by the LED over time;
modifying one or more of the correction coefficients associated with the LED when a difference exists between the measured short circuit current and the previously determined short circuit current measurement; and
when the one or more correction coefficients are modified, using the modified correction coefficients to adjust the output power from the LED by adjusting a current applied to the LED.
2. The display device as recited in claim 1 , wherein the display device is configured to receive light from the light source when the photo-sensitivity is measured.
3. The display device as recited in claim 2 , wherein the display device is configured to receive sunlight when the photo-sensitivity is measured.
4. The display device as recited in claim 2 , wherein the display device is configured to receive a fixed spectrum matching a peak emission wavelength of the LED when the photo-sensitivity is measured.
5. The display device as recited in claim 1 , wherein the correction coefficients are configured to compensate for a variation in the intensity of light produced by the LED.
6. The display device as recited in claim 1 , wherein the correction coefficients are configured to compensate for a variation in the intensity of light and a wavelength produced by the LED.
7. The display device as recited in claim 1 , wherein the array of LEDs comprises organic LEDs.
8. The display device as recited in claim 1 , wherein the array of LEDs comprises inorganic LEDs.
9. The display device as recited in claim 1 , wherein the array of LEDs is configured to produce a backlight.
10. The display device as recited in claim 9 , wherein the backlight is configured to be modulated on a pixel by pixel basis to produce images.
11. The display device as recited in claim 10 , wherein the backlight is configured to be modulated by liquid crystal.
12. The display device as recited in claim 9 , further comprising a color filter positioned in front of the backlight provided by the array of LEDs and a liquid crystal array positioned in front of the color filter.
13. The display device as recited in claim 12 , further comprising a diffuser and a polarizer positioned between the color filter and the backlight provided by the array of LEDs and further comprising a polarizer in front of the liquid crystal array.
14. The display device as recited in claim 9 , further comprising a liquid crystal array positioned in front of the backlight provided by the array of LEDs without an intervening color filter.
15. The display device as recited in claim 14 , further comprising a diffuser and a polarizer positioned between the liquid crystal array and the backlight provided by the array of LEDs and further comprising a polarizer in front of the liquid crystal array.
16. The display device as recited in claim 1 , wherein the display device is configured to operate within a billboard.
17. The display device as recited in claim 1 , wherein the display device is configured to operate within a direct emission display.
18. The display device as recited in claim 1 , wherein the display device is configured to operate within a projector.
19. The display device as recited in claim 1 , wherein the correction coefficients originally stored in the memory were generated during manufacturing of the display device.
20. The display device as recited in claim 1 , wherein said control circuitry is configured for determining a ratio of the measured open circuit voltage to the measured short circuit current to provide an indication of wavelength variations between LEDs within the array of LEDs.
21. The display device as recited in claim 1 , wherein said control circuitry is further configured for:
comparing the measured open circuit voltage with an open circuit voltage measurement previously determined while illuminating the LED with the light source; and
modifying one or more of the correction coefficients associated with the LED when a difference exists between the measured open circuit voltage and the previously determined open circuit voltage measurement.
22. The display device as recited in claim 21 , wherein the previously determined open circuit voltage measurement and the previously determined short circuit current measurement were determined during manufacturing of the display device and stored in the memory.
23. A method for operating a display device having an array of LEDs configured to produce light for the display device, and a memory for storing correction coefficients, which are associated with the array of LEDs and used to compensate for variations in the light produced by the array of LEDs, the method comprising:
measuring a photo-sensitivity of an LED within the array of LEDs by measuring an open circuit voltage and a short circuit current induced across the LED when the LED is illuminated with a light source;
comparing the measured short circuit current to a short circuit current measurement previously determined while illuminating the LED with the light source to provide an indication of a variation in intensity of light produced by the LED over time;
modifying one or more of the correction coefficients associated with the LED when a difference exists between the measured short circuit current and the previously determined short circuit current measurement; and
when the one or more correction coefficients are modified, using the modified correction coefficients to adjust an output power from the LED by adjusting a current applied to the LED.
24. The method as recited in claim 23 , wherein the measuring step is conducted using the light source to illuminate the display device.
25. The method as recited in claim 24 , further comprising utilizing sunlight as the light source.
26. The method as recited in claim 24 , further comprising utilizing a fixed spectrum matching a peak emission wavelength of the LED as the light source.
27. The method as recited in claim 23 , wherein when the one or more correction coefficients are modified, the method further comprises using the modified correction coefficients to compensate for variations in the intensity of light produced by the LED.
28. The method as recited in claim 23 , wherein the array of LEDs comprises organic LEDs.
29. The method as recited in claim 23 , wherein the array of LEDs comprises inorganic LEDs.
30. The method as recited in claim 23 , further comprising utilizing the array of LEDs to produce a backlight.
31. The method as recited in claim 30 , further comprising modulating the backlight on a pixel by pixel basis to produce images.
32. The method as recited in claim 31 , wherein the modulating step comprises modulating the backlight by liquid crystal.
33. The method as recited in claim 30 , further comprising color filtering light from the backlight and then modulating the color filtered light using a liquid crystal array.
34. The method as recited in claim 33 , further comprising diffusing and polarizing the light from the backlight prior to the color filtering step.
35. The method as recited in claim 30 , further comprising modulating light from the backlight using a liquid crystal array without an intervening color filtering.
36. The method as recited in claim 35 , further comprising diffusing and polarizing the light from the backlight prior to the modulating step.
37. The method as recited in claim 23 , further comprising operating the display device as part of a billboard.
38. The method as recited in claim 23 , further comprising operating the display device as part of a direct emission display.
39. The method as recited in claim 23 , further comprising operating the display device as part of a projector.
40. The method as recited in claim 23 , wherein the correction coefficients were generated during manufacturing of the display device.
41. The method as recited in claim 23 , further comprising measuring a ratio of the open circuit voltage to the short circuit current to provide an indication of wavelength variations between LEDs within the array of LEDs.
42. The method as recited in claim 41 , further comprising using the correction coefficients to compensate for variations in intensity of light and wavelength produced by the LED.
43. The method as recited in claim 23 , further comprising:
comparing the measured open circuit voltage with an open circuit voltage measurement previously determined while illuminating the LED with the light source; and
modifying one or more of the correction coefficients associated with the LED when a difference exists between the measured open circuit voltage and the previously determined open circuit voltage measurement.
44. The method as recited in claim 43 , wherein the previously determined open circuit voltage measurement and the previously determined short circuit current measurement were generated during manufacturing of the display device and stored within a memory within the display device.