An electronic system includes a control circuit to provide a binary control signal alternating between a first binary state during first phases and a second binary state during second phases; a screen controlled by the control signal, the screen emitting light during each first phase, and to not emit any light during each second phase; a light sensor under the screen or along the edge of the screen, and providing a measurement signal representative of a quantity of light received by the sensor during a measurement phase or a plurality of consecutive measurement phases; and a synchronization device to synchronize each measurement phase with a second phase.