TYPES BASED ON RESPONSE TO PHOTOPERIOD
short-day plant (SDP) - plants that exhibit their photoperiodic response when the
photoperiod is shorter than a critical photoperiod.
plant (LDP) - plants
that exhibit their photoperiodic response when the
day-neutral plant (DNP) - plants that are not affected by photoperiod.
twilight - reflected sky light that occurs approximately 1/2
hour before sunrise and
1/2 hour after sunset.
Plants can detect civil twilight, so it must be taken into account when determining the photoperiod that plants perceive. Plants cannot detect moonlight, so it does not effect the photoperiod plants perceive.
- the day length a plant perceives, which will be the absolute day length
photoperiod - the photoperiod (absolute day length + civil twilight)
above or below
Each species has its own unique critical photoperiod that it "looks" for.