An illumination level of a luminous element of a user interface for an electrical device is controlled by a processor driving the luminous element with a pulse-width-modulated (PWM) or other type of control signal that is calculated based on a) a signal corresponding to a desired time-varying illumination level of the luminous element to be perceived by a human observer and b) a nonlinear sensitivity relationship between an actual illumination level and a resulting illumination level perceived by a human eye, wherein the corresponding signal comprises an increasing sinusoidal-based ramp function and a decreasing sinusoidal-based ramp function.