Circadian clocks are not engineered but evolved through evolutionary tinkering by natural selection. In this issue, Joo et al. (pp. 572–587) show that the circadian clock in plants allows them to selectively pay attention to light signals rather than simple wake-up in anticipation of the rising sun. The authors measured photosynthetic rates of dark-adapted wildtype and clock-silenced plants throughout a 24-h day under field and laboratory conditions.