Plant Responses to Light-Dark Cycles

Based on their requirement for day length (number of hours of light) for flowering plants have been grouped under three major categories,

1. Short-day
2. Long-day and
3. Day-neutral plants

Figure: A diagrammatic representation to show the difference between a short-day plant (SDP) and a long-day plant (LDP). A SDP requires more than a critical period of darkness. In this case SDP needed more than 8 hrs of darkness or less than 16 hours of light to flower. A LDP requires a less than a critical hour of darkness or more than a certain hours of light. In this ease, LDP required more than 10 hours of light to flower.