This circuit, from a publication of the 1970s, can compare the intensity of two light sources, using for this purpose two separate detectors. The circuit can be assembled with current transistors such as the BC558 and the sensors can be photodiodes of any type. The indication can be made by a common multimeter in the voltage scale connected in LR or even a small bulb of 20 mA. The power can also be made with 6 V
Material:
R1, R2 - 47k
R3, R4-2k2
T5. R6 - 180 R
