An experiment conducted in the controlled-environment rooms (CERs) of the Phytotron at North Carolina State University contrasted the relative biological effectiveness of the square photoperiod with abrupt light-dark transitions, and a sequenced photoperiod, with stepped transitions from dark to full light. The square photoperiod produced greater total plant growth and a narrower shoot: root ratio than a sequenced photoperiod which delivered equal photosynthetically active radiance (PAR). For reproducing the characteristic growth of a field plant within CERs neither the square photoperiod nor the sequenced photoperiod offered decisive advantages. However, the less-than maximum daylight irradiance within CERs was not a restricting factor in achieving quantity of growth expected for field performance.

(Full article published with kind permission from "Tobacco International")