A method of determining the relative sizes of subpixels in a OLED display device having a display pixel that includes a plurality of subpixels of different colors, wherein the subpixels are different in size, wherein the relative sizes (Ai) of the subpixels (i) are based on the emission efficiency of the subpixels, the chromaticity of a target display white point, and the relative luminance stability over time of the subpixels thereby protecting the subpixels whose emission efficiency is low from prematurely deteriorating, comprising the steps of: a) measuring chromaticity coordinates for the subpixels (i); b) selecting aim chromaticity coordinates (x w, y w) and luminance (Y w) of a target display white point; c) calculating a required luminance (Y i) output from the display to create the selected target display white point for each subpixel (i) using the chromaticity coordinates of the subpixels, and the aim chromaticity coordinates and the luminance of the target display white point; d) selecting an initial light emissive area (A i) for each subpixel (i); e) providing an optical transmission factor for each subpixel (i); f) calculating an actual luminance (Y i) for each subpixel using the initial areas (A i) and optical transmission factors for the subpixel (i); g) determining a functional relationship between current density (I i) and luminance output for each subpixel (i); h) calculating an aim current density (I i) for each subpixel (i); i) determining a functional relationship between current density (I i) and a luminance stability over time (T i) for each subpixel (i), wherein the luminance stability over time (T i) is the time until the light-emitting element has lost half its original luminance; j) calculating the time (T i) representing the luminance stability over time for each subpixel (i) using the aim current density (I i) and the luminance stability function; and k) if the times (T i) are unequal, modifying the light emissive areas (A i) of the subpixels (i) by stacking multiple layers of light emitting materials of the same color, reducing the area (A i) of the subpixel (i) with the larger time (T i) and increasing the area (A i) of the subpixel with the smaller time (T i), and repeating steps h, j, and k until the times (T i) are equal. a) measuring chromaticity coordinates for the subpixels (i); b) selecting aim chromaticity coordinates (x w, y w) and luminance (Y w) of a target display white point; c) calculating a required luminance (Y i) output from the display to create the selected target display white point for each subpixel (i) using the chromaticity coordinates of the subpixels, and the aim chromaticity coordinates and the luminance of the target display white point; d) selecting an initial light emissive area (A i) for each subpixel (i); e) providing an optical transmission factor for each subpixel (i); f) calculating an actual luminance (Y i) for each subpixel using the initial areas (A i) and optical transmission factors for the subpixel (i); g) determining a functional relationship between current density (I i) and luminance output for each subpixel (i); h) calculating an aim current density (I i) for each subpixel (i); i) determining a functional relationship between current density (I i) and a luminance stability over time (T i) for each subpixel (i), wherein the luminance stability over time (T i) is the time until the light-emitting element has lost half its original luminance; j) calculating the time (T i) representing the luminance stability over time for each subpixel (i) using the aim current density (I i) and the luminance stability function; and k) if the times (T i) are unequal, modifying the light emissive areas (A i) of the subpixels (i) by stacking multiple layers of light emitting materials of the same color, reducing the area (A i) of the subpixel (i) with the larger time (T i) and increasing the area (A i) of the subpixel with the smaller time (T i), and repeating steps h, j, and k until the times (T i) are equal.