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Historically displays used three colorants in an additive system. During that time, the CIE chromaticity diagram adequately illustrated color capability. Modern displays are not constrained by this additive architecture, and the diagram can fail in its purpose. This is demonstrated by analysis and a large number of display measurements. A device‐independent methodology using CIE 1976 L*a*b* color gamut volume is described that provides a robust means to determine the size of the color gamut. This methodology is then extended to the ‘gamut rings’ diagram as a solution for visualizing color capability that directly correlates to color gamut volume. It is further shown how the methodology can be applied to determine the intersection between two gamut volume boundaries.

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We demonstrate a significant improvement in the external electroluminescence efficiency of red-emitting polymer light emitting diodes (LEDs) by modifying the optical structure of the device. By using a cathode composed of a thin (5nm) film of calcium backed with an optically thick film of silver, we measured improvements in the external efficiency of polymer LEDs by a factor of 1.6 times compared to a device using a cathode composed of calcium backed with lower reflectivity aluminum. By incorporating the LED into a microcavity structure (to form a resonant cavity LED) it is possible to obtain additional (but rather smaller) improvements in external efficiency of the order of 1.15 times, compared to a standard LED utilizing the same cathode. By combining high reflectivity cathode∕mirror materials with a low finesse cavity structure, we show that the external efficiency of a LED can be improved by as much as 1.8 times compared to a standard (noncavity) LED. Our results are in good agreement with those of theoretical calculations and demonstrate the real improvements in device external efficiency that can be achieved by reducing optical losses within the LED structure.