Examples from the Web for photoperiod
These captives had been kept for several months at a temperature of 21 degrees Centigrade, and on a daily photoperiod of 15 hours.
The mice were kept in a room in which temperature and photoperiod were controlled.
Broad limits to functional reproductive activity seem to be set by the photoperiod—neuroendocrine system.The Breeding Birds of Kansas|Richard F. Johnston
In general, Tb's showed a marked circadian cycle in phase with photoperiod.