photoperiod
noun
pho·to·pe·ri·od
ˌfō-tō-ˈpir-ē-əd 
: a recurring cycle of light and dark periods of constant length
also
: photophase sense 2
Examples of photoperiod in a Sentence
Recent Examples on the Web
The prompt to begin growing a fresh set of antlers is regulated by a rise in testosterone, which is triggered by photoperiod.
—
Andrew McKean, Outdoor Life, 17 Apr. 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
Species have evolved sensitivity to how much light is available in a 24-hour window, and that cue — the photoperiod — has been shown to influence a range of behaviors, from plant growth to hibernation, to migration, and to reproduction.
—Quanta Magazine, 18 June 2024
Inside the $45 packet were five feminized, photoperiod seeds from Gogol’s Oregon farm, and they can be purchased with no more hassle — or stigma — than anything else at C&S Garden Center.
—Adam Tschorn, Los Angeles Times, 20 May 2024
The best autoflower seeds for sale also boast a shorter flowering time than photoperiod plants, which means that maintenance time is reduced on your end.
—Anna Miller, Sacramento Bee, 26 Apr. 2024
On the other hand, there's the findings of sleep psychiatrist Thomas Wehr, in particular his classic 1992 study called In short photoperiods, human sleep is biphasic.
—Neuroskeptic, Discover Magazine, 29 Apr. 2010
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Andrew McKean, Outdoor Life, 17 Apr. 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
Species have evolved sensitivity to how much light is available in a 24-hour window, and that cue — the photoperiod — has been shown to influence a range of behaviors, from plant growth to hibernation, to migration, and to reproduction.
—Quanta Magazine, 18 June 2024
Inside the $45 packet were five feminized, photoperiod seeds from Gogol’s Oregon farm, and they can be purchased with no more hassle — or stigma — than anything else at C&S Garden Center.
—Adam Tschorn, Los Angeles Times, 20 May 2024
The best autoflower seeds for sale also boast a shorter flowering time than photoperiod plants, which means that maintenance time is reduced on your end.
—Anna Miller, Sacramento Bee, 26 Apr. 2024
On the other hand, there's the findings of sleep psychiatrist Thomas Wehr, in particular his classic 1992 study called In short photoperiods, human sleep is biphasic.
—Neuroskeptic, Discover Magazine, 29 Apr. 2010
Cite this Entry
“Photoperiod.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/photoperiod. Accessed 31 Oct. 2025.
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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