Abstract: A lighting device for a bicycle comprising at least one light emitter and a controller programmed to vary the brightness and/or flash rate and/or flashing pattern of the at least one light emitter based upon the measurement of the motion of the device. The controller may be provided with sensor means to measure one or more of the acceleration, orientation and rate of change of orientation of the device, wherein the controller compares the measured acceleration, orientation and/or rate of change of orientation with reference data contained in predetermined look-up tables to determine a risk score, the controller selecting the brightness and/or flash rate and/or flashing pattern of the at least one light emitter as a function of the risk score.