LED device compensation method

• US 7,847,764 B2
• Filed: 03/15/2007
• Issued: 12/07/2010
• Est. Priority Date: 03/15/2007
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Inventors: Leon, Felipe A., Cok, Ronald S., Ludwicki, John E.
• Primary Examiner(s): Shalwala; Bipin
• Assistant Examiner(s): Abebe; Sosina
• Application Number:
  US11/686,642
• Publication Number:
  US 20080224966A1
• Time in Patent Office: 1,363 Days
• Field of Search: 345 55-102, 345204-214, 345/77, 345/78, 345/82, 315149-159, 315/169.3
• US Class Current: 345/77
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/048 using evaluation of the usage time
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/60 Circuit arrangements for operating LEDs comprising organic material, e.g. for operating organic light-emitting diodes [OLED] or polymer light-emitting diodes [PLED]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A method for controlling and compensating aging in an LED device includes measuring a performance change in light output of the LED device. The LED device is controlled with a first compensation algorithm derived from the measured performance change, during a first period, to effect a luminance change over time in the light output of the LED device. Subsequently, a second compensation algorithm, derived from the measured performance change, and different from the first compensation algorithm, during a second period, effects a second luminance change over time in the LED device'"'"'s light output. The second luminance change over time in the second period is different from the first luminance change over time in the first period. Furthermore, the first and second periods together are less than the lifetime of the LED device.

Claims

1. A method for controlling and compensating aging in an LED device comprising the steps of:

a) measuring a performance change in light output of the LED device;

b) controlling the LED device with a first compensation algorithm derived from the measured performance change, during a first period, to effect a luminance change over time in the light output of the LED device; and

c) controlling the LED device with a second compensation algorithm, derived from the measured performance change, different from the first compensation algorithm, during a second period, to effect a second luminance change over time in the LED device'"'"'s light output;

wherein the second luminance change over time in the second period is different from the first luminance change over time in the first period;

wherein the first and second periods together are less than the lifetime of the LED device and

wherein either step of controlling the LED device restricts the current, voltage, or power supplied to the LED device to less than that necessary to maintain a constant luminance over time.

2. The method claimed in claim 1 wherein either step of controlling the LED device reduces the current, voltage, or power supplied to the LED device.

3. The method claimed in claim 1 wherein the LED device is a display device or a lamp.

4. The method claimed in claim 1 wherein the LED device is an organic LED device.

5. The method claimed in claim 1 wherein no compensation algorithm is employed after the end of the second period.

6. The method claimed in claim 1 further employing a compensation algorithm after the second period until the LED device'"'"'s light output fails.

7. The method claimed in claim 1 further comprising the step of controlling the LED device with a third compensation algorithm during a third period to effect a third luminance change over time in the LED device'"'"'s light output.

9. The method claimed in claim 1 further comprising the step of measuring the performance change in the LED device a plurality of times during one or more periods.

10. The method claimed in claim 1 wherein the first compensation algorithm allows the luminance of the LED device to change at a first rate during the first period and the second compensation algorithm allows the luminance of the LED device to change at a second rate different from the first rate during the second period.

11. The method claimed in claim 1 wherein the first compensation algorithm allows the luminance of the LED device to decrease at a first rate during the first period and the second compensation algorithm allows the luminance of the LED device to be maintained at a constant luminance value during the second period.

12. The method claimed in claim 1 wherein either the first or second compensation algorithm maintains a constant average LED device luminance.

13. The method claimed in claim 1 wherein an end to the first or second period is specified by the relative luminance of the LED device at the beginning and end of the respective period.

14. The method claimed in claim 1 wherein an end to the first or second period is specified by a relative change in current, voltage, or power provided to the LED device, or when a maximum current, voltage, or power is supplied to the LED device.

15. The method claimed in claim 1 wherein the first or second compensation algorithm controls the device peak luminance versus time such that constraints are placed on the maximum relative current density for the maximum average sub-pixels at any time, the maximum relative current density for the maximum average sub-pixels that depend on the age of the display, the maximum rate of change of the display peak luminance over time, or the maximum rates of change of the LED device peak luminance that depends on the age of the display.

16. The method claimed in claim 1 wherein the compensation algorithm is selected from one or more of the group including a voltage applied to the display;

a voltage applied to each pixel;

a charge applied to each pixel; and

a data value applied to each pixel.

17. The method claimed in claim 1 wherein the LED device is a color display comprising light-emitting elements, emitting different colors of light and where a different compensation algorithm controls each color of light-emitting element.

18. The method claimed in claim 1 wherein different compensation algorithms control the LED device at different LED device luminance levels.

8. The method claimed in claim I wherein the LED device is an inorganic LED device employing quantum dots.

19. A method for controlling and compensating aging in an LED device comprising the steps of:

a) measuring a performance change in light output of the LED device;

b) controlling the LED device with a first compensation algorithm derived from the measured performance change, during a first period, to effect a luminance change over time in the light output of the LED device;

c) controlling the LED device with a second compensation algorithm, derived from the measured performance change, different from the first compensation algorithm, during a second period, to effect a second luminance change over time in the LED device'"'"'s light output;

wherein the second luminance change over time in the second period is different from the first luminance change over time in the first period; and

d) controlling the LED device with a third compensation algorithm during a third period to effect a third luminance change over time in the LED device'"'"'s light output;

wherein the first and second periods together are less than the lifetime of the LED device.