phototimer
/ˈfoʊ.toʊ.taɪ.mər/Definitions
1. noun
A device that measures time intervals using a light source and photodetector.
“The photographer used a phototimer to synchronize the flash with the model’s pose.”
2. verb
To measure time intervals using a light source and photodetector.
“The scientist phototimed the experiment to capture the precise moment of reaction.”