Algorithms for selecting LEDs to imitate a group of daylight spectra, instead of fixed-spectrum lighting, are based on minimizing two indices. The first index related to the LEDs only is minimized for determining LED candidates. Minimizing the second index obtained by applying the daylight spectra to the candidates achieves a minimax solution. The sum of the second indices of the daylight spectra can be well approximated by that of the average spectrum of the daylight spectra and is treated as a target spectrum for the LED selection. A pruning process is followed to delete redundant LEDs.