Valotusperioodi

Valotusperioodi (from valotus 'exposure to light' and perioodi 'period') is a term used primarily in Finnish-language texts to denote the length of the daily light exposure within a 24-hour cycle. In biology and horticulture, valotusperioodi describes the photoperiod—the amount of light a plant or animal experiences in a day—and is a key environmental cue that influences physiological processes.

In plants, valotusperioodi governs photoperiodism, affecting flowering time, tuber formation, and dormancy. Short-day plants flower when night length exceeds a species-specific threshold, while long-day plants require a night shorter than a threshold. Some plants are day-neutral, showing limited sensitivity to photoperiod. Light intensity and spectrum interact with valotusperioodi to modulate responses.

In animals, photoperiod influences reproductive cycles, molt, and circadian rhythms; melatonin secretion in the pineal gland is often a mediating factor. The concept is used in agricultural settings to optimize growth and yield: artificial lighting schedules are designed to achieve desired valotusperioodi, sometimes coupled with temperature and nutrition controls.

Measurement: valotusperioodi is typically expressed in hours of light per 24-hour cycle, and can be adjusted with timers, LEDs, and shading. Ecological studies may track seasonal changes and regional variations in natural photoperiod.

See also: photoperiodism; circadian rhythm; melatonin.

Notes: The term is chiefly found in Finnish literature; photoperiod is the common English equivalent.