Maize is a short-day photoperiod sensitive crop. Tropical maize is especially photoperiod sensitive and will exhibit delayed flowering, an increased leaf number, and reduced yield under long-day conditions. We would like to identify the genes that contribute to maize photoperiod sensitivity. To accomplish this, we have developed photoperiod insensitive x sensitive RIL populations. In this study, we have determined when and how to induce an effective photoperiod in the parental lines of our RIL populations. The results of this initial investigation will be useful when measuring photoperiod sensitivity in the RIL populations.