lyscyklus

Lyscyklus, or light cycle, is the repeating pattern of illumination that organisms experience over time, typically a 24-hour day. It acts as a key environmental cue that interacts with internal biological clocks to regulate physiology, behavior, and development.

Plants respond to photoperiod, the length of the light period within a cycle. Short-day plants flower when nights exceed a critical length, while long-day plants require longer days to flower. The most common starter regime in cultivation is around 12 hours of light and 12 hours of dark, but exact requirements vary by species. Plants use photoreceptors such as phytochromes and cryptochromes to detect red, far-red, and blue light, enabling the circadian clock to synchronize growth and flowering signals, including florigen production and movement to the shoot apex.

Animals also rely on the light cycle to regulate circadian rhythms. Light information from the retina serves as a Zeitgeber that aligns the internal clock, typically centered in the brain, to the external day-night cycle. This influences sleep, metabolism, hormone release, and seasonal behaviors, including reproduction in some species through melatonin signaling during dark periods.

Practically, lyscyklus is managed in agriculture, horticulture, and laboratory settings to optimize growth, flowering, and welfare. Lighting conditions vary in intensity, spectrum, and duration, and slight changes can have measurable effects. Concerns include energy use, light pollution, and the welfare implications of non-natural light schedules.