The invention proposes an improved illumination system (1). The illumination system (1) comprises: an LED module (2) having at least one LED or OLED; at least one light sensor (3); and a control circuit (4) designed to control the current flowing through the LED module (2), and to be supplied with an individual sensing signal of each of the at least one light sensor (3). The at least one light sensor (3) is designed such that: the light sensor (3) has its sensitivity peak set to be at a lower wavelength than the spectrum emitted by the LED module (2), preferably below 420 nm, more preferably below 410 nm, and/or the light sensor (3) has its sensitivity peak set to be at a higher wavelength than the spectrum emitted by the LED module (2), preferably above 680 nm. Furthermore, the invention proposes a method for calibrating the illumination system (1). The control circuit (4) is designed to calculate a crosstalk calibration value, by detecting the contribution of a switching on or increasing of the current through the LED module (2) in a non-ambient light state, on the basis of the supplied detection signals.