In a circuit arrangement for carrying out light intensity measurements,
comprising an input terminal (5), an output terminal (6), a first and a
second photodiodes (D.sub.1, D.sub.2) for receiving light emitted by an
optical light source (S) and a first and a second operational amplifiers
(1, 2) for receiving output current signals of the first and second
photodiodes (D.sub.1, D.sub.2) generated under influence of the emitted
light, the novelty lies in further comprising a four branch bridge circuit
including in two adjacent branches the first and second photodiodes
(D.sub.1, D.sub.2) coupled to a common point by their respective poles of
the same sign and oppositely to them in the further two adjacent branches
two bridge resistors (R.sub.1, R.sub.2), a third operational amplifier (3)
for supplying power to the optical light source (S), current generator
means connected by its input to the input terminal (5) and by its one
output to the common point and an input of the third operational amplifier
(3) for driving the bridge circuit, wherein the first operational
amplifier (1) is inserted between the first photodiode (D.sub.1) and the
junction point of the bridge resistors (R.sub.1, R.sub.2), and the second
operational amplifier (2) is connected by its input to the second
photodiode (D.sub.2) and by its output led to the output terminal (6) is
reversely connected to the input by means of a compensation resistor
(R.sub.k).