guided to the window 12 and diffuse light passes through the window 12 and enters the interior of the optical non transparent housing 11 having a lambertian ray pattern this ray pattern will transmit through an optical non diffuse material e g glass or air depending on the angle of incidence light of a certain wavelength range passes the interference filter 13 as described above with reference to fig1 the electric signals resulting from the detection of the transmitted light by means of the photo sensors 14 are processed by the control electronics not shown which are external in this case taking e g into account the interference filter 13 transmission wavelength at a defined angle of incidence the geometrical arrangement of the window 12 the photo sensors 14 and the shape and extension of the photo sensors 14 themselves in this embodiment the detected signals of three photo sensors 14 having a semi circular shape with the first photo sensor in the center the second semi circular photo sensor with a semi circular notch arranged around the first photo sensor and the third semi circular photo sensor with a semi circular notch arranged around the second photo sensor are transmitted to the control electronics the window 12 is a pinhole position above the center of the first photo sensor the electronic control signals transmitted from the photo sensors are used.