Physiology
Photoperiod
The relative length of light and dark periods in a 24-hour cycle. Many organisms use photoperiod as a reliable cue for seasonal timing of reproduction, migration, and dormancy.
Biological Context
Unlike temperature, which fluctuates unpredictably, day length is a reliable predictor of season. Plants use photoperiod to time flowering; birds use it to trigger migration; mammals use it to time reproduction. The pineal gland detects photoperiod through melatonin secretion patterns.
Business Application
Business 'photoperiods': reliable leading indicators of market cycles. Quarterly earnings seasons, annual budget cycles, and industry trade shows create predictable patterns. Companies that align their rhythms to market photoperiods optimize timing of launches and investments.