Updated project metadata. In this study we developed an experimental set-up to study variation in twilight length using recently developed 7-band LED lights with fully programmable spectra and sigmoidal ramping of light intensity in controlled growth chambers. We employed this set-up to gain a comprehensive understanding of the impact of changing twilight lengths on Arabidopsis thaliana (Col-0) plants at both physiological and molecular levels. We studied the effect of a wide range of twilight lengths (0 min, 15 min, 30 min, 60 min, 90 min) on plant growth.