photoperiod

noun

pho·​to·​pe·​ri·​od ˌfō-tō-ˈpir-ē-əd 

: a recurring cycle of light and dark periods of constant length

also : the period of light during such a cycle: photophase sense 2

photoperiodic

ˌfō-tō-ˌpir-ē-ˈä-dik 

adjective

photoperiodically

ˌfō-tō-ˌpir-ē-ˈä-di-k(ə-)lē 

adverb

Examples of photoperiod in a Sentence

Recent Examples on the Web

There are some tree species triggered by photoperiod and will turn just because of that. — Stephen Underwood, Hartford Courant, 24 Aug. 2026

Light and noise emitted from the data center could dramatically affect the behavior of the zoo animals by disrupting their natural photoperiods, the time during which an animal is exposed to light. — Michelle Del Rey, USA Today, 10 June 2026

The shutdown is triggered primarily by photoperiod, not temperature. — John Drake, Forbes.com, 28 May 2026

Most of the birds that are important to the Louisiana duck hunter harvest are photoperiod migrators [such as teal]. — Natalie Krebs, Outdoor Life, 14 Jan. 2026

Word History

First Known Use

1920, in the meaning defined above

Rhymes for photoperiod

• myriad
• period

Kids Definition

photoperiod

noun

pho·​to·​pe·​ri·​od ˌfōt-ō-ˈpir-ē-əd 

: a recurring cycle of light and dark periods as it affects the growth and functioning of a plant or animal

Medical Definition

photoperiod

noun

pho·​to·​pe·​ri·​od ˌfōt-ō-ˈpir-ē-əd 

: a recurring cycle of light and dark periods of constant length

photoperiodic

-ˌpir-ē-ˈäd-ik 

adjective

photoperiodically

-i-k(ə-)lē 

adverb