An illumination system correlates solar time to a clock and controls lighting or illumination based on time. The illumination system may turn ON light source(s) at a first level at a turn ON time, correlated to be around or at dusk, and turn OFF light source(s) at a turn OFF time, correlated to be around or at dawn. The illumination system may reduce a level of light output, and hence power consumption, at a time after turning ON a light source, and increases the level of light output at a time prior to turning OFF the light source. Turn ON, turn OFF, decrease and increase times may be determined based on recent levels of light or illumination in the environment, for example via average or median levels over a number of previous daily cycles. Filtering may eliminate aberrant events.