Mapping apparatus includes a transmitter, which is configured to emit at least one beam including a sequence of pulses of light toward a plurality of points in a scene. A receiver is configured to receive the light reflected from the scene and to generate an output indicative of a time of flight of the pulses to and from the points in the scene. A processor is coupled to process the output of the receiver so as to generate a 3D map of the scene, while controlling a power level of the pulses emitted by the transmitter responsively to a level of the output from the receiver in response to one or more previous pulses.