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Meaning of photoperiod

pho•to•pe•ri•od

Pronunciation: (fō"tu-pēr'ē-ud), [key]
— n. Biol.
  1. the interval in a 24-hour period during which a plant or animal is exposed to light.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.