Flashes per minute (FPM) is simply the number of times a flashing light blinks per

minute The minute is a unit of time usually equal to (the first sexagesimal fraction) of an hour, or 60 seconds. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds (there is a provision to insert a n ...

. Police and emergency vehicles use warning lights with flashing rates that typically fall in a range from 60 to 240 FPM. In North America,

grade crossing A level crossing is an intersection where a railway line crosses a road, path, or (in rare situations) airport runway, at the same level, as opposed to the railway line crossing over or under using an overpass or tunnel. The term a ...

signals have a flashing rate ranging between 45 and 65 FPM with the ideal rate being 60 FPM. Persons with

photosensitive epilepsy Photosensitive epilepsy (PSE) is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights; bold, regular patterns; or regular moving patterns. PSE affects approximately o ...

may suffer a seizure in response to a specific flashing frequency, e.g. 420 FPM, but the exact triggering frequency varies across individuals. To minimize the likelihood of an epileptogenic response, flashing rates above 300 FPM (5 Hz) should be avoided (Harding and Jeavons, 1994). For conversion purposes, 60 FPM = 1 Hz (i.e. a frequency of one per second).

References

Harding G F A & Jeavons P M, 1994. ''Photosensitive Epilepsy''. London: MacKeith Press. Lighting Units of frequency