Phototransistor vs. temperature

I’m using the Imp’s built-in light sensor to monitor a flashing outdoor light. The readings, both “ON” and “OFF” vary considerably from day to day. Could it be that temperature affects the sensitivity of the photo-transistor?

Shouldn’t do, to any real extent. Sure it’s not just light leakage? A lot comes in through the top cover of the imp unless you mask it off.

Thank you for responding. I’ll try masking, but I doubt if that is the issue, because there is no other source of light other than the one I am monitoring. Something is causing the readings, both ON and OFF, to vary from day to day.

Is the flashing light on during the day, or night?
“from day to day”, or “night to night”?

The light flashes only during darkness (night), so the variation is, as you suggest, “from night to night.”

Could this be the power supply you’re using changing with temperature? The light sensor is attached to the same power rail as the chip, so the reading is relative and so shouldn’t be significantly affected though.

Can you define “considerably” eg in percentage terms?

Is it possible that the actual light varies between on and off?

Try a different light sensor like this:

That would be a separate circuit than the imp, thus making the two not affecting each other.