Pixel structure with optimized subpixel sizes for emissive displays

1. A fixed format emissive display comprising: an array of emissive pixel elements, each pixel element comprising at least two sub-pixel elements made of different materials; and areas of the at least two sub-pixel elements being such that lifetimes of the sub-pixel areas are within a predetermined tolerance of each other,

wherein each pixel element displays white at a predetermined white point within a certain tolerance over a lifetime of the pixel element and

wherein the lifetime of the pixel element is determined by a color shift of the pixel element greater than a predetermined value.

2. The fixed format emissive display according to claim 1 , wherein the lifetime of the pixel element is determined by the brightness of the pixel element reducing to a predetermined value compared with an initial value, preferably within the range 40–60%.

3. The fixed format emissive display according to claim 1 , wherein the lifetime of a sub-pixel element is determined by the brightness of the sub-pixel element reducing to a predetermined value compared with an initial value, preferably within the range 40–60%.

4. The fixed format emissive display according to claim 1 , wherein the lifetime of a sub-pixel element is determined by a color shift of the sub-pixel element greater than a predetermined value.

5. The fixed format emissive display according to claim 1 , wherein the predetermined value is a number of JND's.

6. The fixed format emissive display according to claim 5 , wherein the number of JND's is 3.

7. The fixed format emissive display according to claim 1 wherein there are at least three sub-pixels for each pixel element and areas of the at least three sub-pixel elements are such that the lifetimes of the sub-pixel areas are within a predetermined tolerance of each other.

8. The fixed format emissive display according to claim 1 ; wherein the predetermined tolerance is 20%, more preferably 10%.

9. The fixed format emissive display according to claim 1 , wherein the pixel elements are organic light emitting diodes.

10. A method of designing a fixed format emissive display using a computing device having a processor and a memory, the display comprising an array of emissive pixel elements, each pixel element comprising at least two sub-pixel elements made of different materials; the method comprising: selecting areas of the at least two sub-pixel elements so that each pixel element displays white at a predetermined white point within a certain tolerance, and modifying the areas of the at least two sub-pixel elements to optimize a lifetime of one or more elements of the display, and

wherein the lifetime of the pixel element is determined by an estimated color shift of the pixel element greater than a predetermined value.

11. The method according to claim 10 , wherein display elements to be optimzed are the sub-pixel elements and the lifetimes of the sub-pixel elements are optimized to within a predetermined tolerance of each other.

12. The method according to claim 11 , wherein the lifetime of a sub-pixel element is determined by the estimated brightness of the sub-pixel element reducing to a predetermined value compared with an initial value, preferably within the range 40–60%.

13. The method according to claim 11 , wherein the lifetime of a sub-pixel element is determined by an estimated color shift of the sub-pixel element greater than a predetermined value.

14. The method according to claim 10 , wherein the display elements to be optimized are the sub-pixel elements and the sub-pixel areas are optimized so that each pixel element displays white at a predetermined white point within a certain tolerance over the lifetime of the pixel element.

15. The method according to claim 14 , wherein the lifetime of the pixel element is determined by the estimated brightness of the pixel element reducing to a predetermined value compared with an initial value, preferably within the range 40–60%.

16. The method according to claim 10 , wherein the predetermined value is a number of JND's.

17. The method according to claim 16 , wherein the number of JND's is 3.

18. The method according to claim 10 , wherein there are at least three sub-pixels for each pixel element and areas of the at least three sub-pixel elements are optimized such that the lifetimes of the sub-pixel areas are within a predetermined tolerance of each other.

19. The method according to claim 10 ; wherein the predetermined tolerance is 20%, more preferably 10%.

20. The method according to claim 10 , wherein the pixel elements are organic light emitting diodes.

21. The method according to claim 10 , further comprising: calculation of a temperature of each sub-pixel element when each pixel element displays white at the predetermined white point, and calculating an aging effect on each sub-pixel element based on the calculated temperature.

22. The method according to claim 10 , wherein the display is powered by a battery and the display element to be optimized is the battery, wherein the sub-pixel areas are optimized to optimize an estimated battery lifetime between charging over the lifetime of the pixel elements.

23. A computer program product comprising software, the software having code for, when the code is executed on a computing device, selecting areas of at least two sub-pixel elements of a display and modifying the areas of the at least two sub-pixel elements to optimize a lifetime of one or more elements of the display whereby the lifetime of the elements is determined by an estimated color shift of the elements greater than a predetermined value.