I'm doing a school project and I want to measure the difference in time that the lights are on in a classroom with and without a motion sensor controlling them. I haven't really found anything about recording how long sensors act or the time between activations. How could I possibly do this?

  • For what exactly have you googled? When using the terms "arduino measure time" you get pretty good results.
    – chrisl
    Mar 22, 2021 at 18:51
  • you don't need an arduino to do this ... get two electrically powered mechanical clocks ... one always runs ... the other is powered by the switched circuit
    – jsotola
    Mar 22, 2021 at 20:03

1 Answer 1


I would consider placing a light sensor close to one of the lights to signal when the lights are on. Placement is critical as you do not want a signal when the lamp is off. I am assuming they are permanent light fixtures and you are not allowed to tamper with the wiring. Record the elapsed time when they are on. Note the start time and then subtract that from the current time based on your watch. For elapsed time and subtract the ontime from that. With the sensor you can also record each time the light is turned on etc. That would all be in your software.

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