A photosensitive detector (1) for detecting luminous flashes (2) is provided with a photosensitive diode (3) which is linked to a positive voltage and to ground via a resistor R1 and which is capable of transforming the luminous flashes into electrical signals and a circuit (4) that processes the electrical signals generated by the photosensitive diode (3). The circuit (4) causes electrical signals which correspond to luminous flashes (2) received by the photosensitive diode (3) and which exhibit a fast rise time to be strengthened, and the circuit (4) causes electrical signals which correspond to luminous flashes (2) received by the photosensitive diode (3) and which vary more slowly in intensity to be attenuated. The circuit (4) is linked directly to the photosensitive diode (3) and includes a differentiator circuit. The differentiator circuit has a differential amplifier (5) with a non-inverting input linked to a connection point situated between the photosensitive diode and the resistor R1, an inverting input linked to ground via a capacitor and to the connection point via a resistor Rx, and an output, and the differential amplifier (5) also has a resistor R2 linked to a connection point between the capacitor and the inverting input.