As a part of a dissertation DI Andreas Winkler is developing methods for the characterization of metal surfaces based on the bidirectional reflectance distribution function. For the calibration of the used camera system, a homogeneous light source with variable illuminance and correlated color temperature (CCT) is necessary. For this purpose, an integrating sphere with two types of high-power light-emitting diodes with different CCT is used.
Due to the dependence of CCT on the current flow through the light-emitting diodes and the impact of warming on illuminance and CCT, a control system is required. In this bachelor thesis, a control system is designed and implemented on a microcontroller. Furthermore, a circuit for controlling the light-emitting diodes is developed, which enables to vary the current flow. For the measurement of the two quantities to be controlled, a suitable sensor is selected and integrated in the control loop.
Finally, the operation of the control system is checked by static setpoints and a sequence of step functions. Also the characteristics of the light-emitting diodes and the influence of heating are recorded.
Keywords: illuminance, CCT, multi-variable control system, integrating sphere, high-power light-emitting diodes
August 5th, 2016