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Control system for illuminance and correlated color temperature of an integrating sphere

Stephan Hromecek

Stephan Hromecek

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.

Figure 1: Block diagram of the multi-variable control system.

Figure 1: Block diagram of the multi-variable control system.

Keywords: illuminance, CCT, multi-variable control system, integrating sphere, high-power light-emitting diodes

August 5th, 2016