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
Examples of photoperiod in a Sentence
Recent Examples on the Web
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
Why some cold-weather animals developed this adaptation and others didn’t is less well understood, but the change appears to be set off by the changing number of sunlight hours in the day as winter approaches (called a photoperiod), Rumble said.
—Jonathan Shikes, Denver Post, 30 Dec. 2025
According to Cannabis Business Times, photoperiod cannabis plants rely on changes in light exposure to transition between vegetative and flowering stages, making this time of year pivotal for growers.
—Matt Rozo, The Mercury News, 3 Mar. 2025
This study opens the door to further insights into just how day length (photoperiod) and sun intensity can impact energy levels and help those with more severe 'winter blues' proactively improve seasonal mental wellbeing.
—Bronwyn Thompson
september 29, New Atlas, 29 Sep. 2024
For example, long-distance migratory songbirds set their internal clocks to the photoperiod and use the summer solstice to time their nesting and migration, said Saeedeh Bani Assadi, a biologist at the University of Manitoba.
—Quanta Magazine, 18 June 2024
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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
Why some cold-weather animals developed this adaptation and others didn’t is less well understood, but the change appears to be set off by the changing number of sunlight hours in the day as winter approaches (called a photoperiod), Rumble said.
—Jonathan Shikes, Denver Post, 30 Dec. 2025
According to Cannabis Business Times, photoperiod cannabis plants rely on changes in light exposure to transition between vegetative and flowering stages, making this time of year pivotal for growers.
—Matt Rozo, The Mercury News, 3 Mar. 2025
This study opens the door to further insights into just how day length (photoperiod) and sun intensity can impact energy levels and help those with more severe 'winter blues' proactively improve seasonal mental wellbeing.
—Bronwyn Thompson
september 29, New Atlas, 29 Sep. 2024
For example, long-distance migratory songbirds set their internal clocks to the photoperiod and use the summer solstice to time their nesting and migration, said Saeedeh Bani Assadi, a biologist at the University of Manitoba.
—Quanta Magazine, 18 June 2024
Cite this Entry
“Photoperiod.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/photoperiod. Accessed 16 Jun. 2026.
Copy CitationKids 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
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