The performance characteristics of white light sources based on a multiple-LED approach, in particular dichromatic and trichromatic sources are analyzed in detail. Figures of merit such as the luminous efficacy, color temperature, and color rendering capabilities are provided for a wide range of primary emission wavelengths. Spectral power density functions of LEDs are assumed to be thermally and inhomogeneously broadened to a full width at half maximum of several kT, in agreement with experimental results. A gaussian line shape is assumed for each of the emission bands. It is shown that multi-LED white light sources have the potential for luminous efficacies greater than 400 lm/W (dichromatic source) and color rendering indices of greater than 90 (trichromatic source). Contour maps for the color rendering indices and luminous efficacies versus three wavelengths are given.
A high-reflectivity omni directional reflector (ODR) has been incorporated into a GaInN light-emitting diode (LED) structure. The ODR comprises a transparent, electrically conductive quarter-wave layer of indium tin oxide clad by silver and serves as an ohmic contact to p-type GaN. It is shown that ODR-LEDs have low optical losses and high extraction efficiency. Mesa-structure GaInN/GaN ODR-LEDs emitting in the blue wavelength range are demonstrated and compared to GaInN/GaN LEDs with semitransparent Ni/Au top contacts. The extraction efficiency of ODR-LEDs is higher as compared to conventional LEDs with Ni/Au contacts.