Abstract: A vehicular-borne illumination control system of the invention for vehicular use automatically controls intensity of a signal light source, i.e., center mounted brake signal, as a function of one or more safety-affecting parameters, e.g., deceleration and/or light level or other ambient condition including fog or precipitation as sensed by sensor(s) of the system. MOSFET switching controls energization of the light from vehicle power, with capability of providing different possible illumination levels by duty cycle control. A microcontroller is responsive sensor input for controlling the duty cycle to vary energization of the light source for transition between said different illumination levels. The transition is thus able to be varied according to a time-varying function, as effectively by spiked overdriving or underdriving, to compensate for human physiological inability to perceive change in the different intensity levels or states.