Snow-rithmetic

It started snowing this evening, so I was sent to clear the driveway. En route, I grabbed the camera, and shot this picture looking up at the light of a nearby lamppost.

Look carefully at the snow... every snowflake shows up seven times. Count 'em!

That must mean that there were seven "flashes" of the streetlamp in the time that the shutter was open - which was 1/13s.

Seven strobes of the light in 1/13s means that each strobe must have been approximately 1 / (13 * 7) = 1/91s apart.

The frequency of the British mains supply is 50Hz. So I would guess that this streetlamp is strobing on each half of the cycle, thus generating 100 strobes per second.

You can do the arithmetic backwards too... one hundred strobes per second, we are open for 1/13 of a second 100/13 = 7.7 strobes :-)

Aren't you so glad you read this?