This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. The response of an organism to changes in its photoperiod, especially as indicated by vital processes.

n. the growth, development and other responses of plants and animals according to the length of day and/or night

"An often overlooked indicator is what biologists refer to as photoperiodism, or the amount of light in any given day."

circadian rhythm   

photoperiodic   

resuit    Shorty    duple    rumba    hard-driving