Results of measurement using a magnetic sensor

Question

I am seeking some advice or information regarding a measurement I made using a magnetic sensor. Essentially, to summarize, I measured the socket for a ceiling light using a magnetic sensor, taking the necessary safety precautions. In so doing, in the immediate proximity of the socket, I measured up to 190 microteslas. It is important to note that the measurement was taken with the lightbulb screwed in, but the light bulb was then unscrewed and the lightbulb was measured independently and was found to give a measurement of roughly 60 microteslas so no higher than the background magnetic field strength.

Therefore the measurement of 190 microteslas came from the socket. Additionally, the magnetic field strength in the general area of the socket but not right beside it was roughly 60 microteslas, thus the background magnetic field strength was roughly 60 microteslas. Is this result normal, what explains this result, and can you provide any further information in general regarding this result?

Answer 1

Without knowing more about the situation it is a bit difficult to give a detailed answer. But we can say a few things.

Electric currents produce magnetic fields. So, when the light is turned on and there is a current passing through it, we would expect some magnetic field over and above the background (Earth) field.

The exact details of the magnetic field near the light could be complicated because it will depend on the geometry of any wires in/out of the light, and the currents inside the light itself.

I'm a bit surprised that you were able to measure any magnetic field due to the light at all. Most magnetic field sensors have fairly slow response. Most (household) lights have AC current running through them. So the magnetic field due to the light would be expected to be changing rapidly, and reversing direction periodically, so its value would average out to zero. The sensor would typically measure an average field over a somewhat long time interval (long compared to the period of the AC current). Can you say anything more about the nature of the magnetic field sensor, and details of the light? I'm a little suspicious that the field you are measuring is some other stray field that isn't due to the light at all, because of how difficult it "should" be to measure the field due to the light.