Design of hemispherical cavities for LED-based illumination devices

We present the design procedure for an illumination system based on the association of several emitting diodes in optical cavities with a hemispherical shape. The main purpose of this illumination system is to provide high amounts of monochromatic light over small areas, thus making it adequate for testing radiation-sensing devices. A detailed methodology for the optimization of the optical system, by taking into account both the electro-optical properties of the emitting diodes and the geometry of the cavity, is described. The irradiance on the working plane is increased by using a pulsed current operation mode at low duty cycles for light emitting diodes. The performance of two illumination devices designed with this methodology has been tested through the measurement of some concentrator GaAs solar cells. Current densities up to 5 A/cm(2)s have been obtained in these cells with a cavity based on infrared emitting diodes.