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This is a weird problem: When I turn on a tube light in my room while my Lenovo G770 laptop is on, the laptop makes the as if a new device is attached to the laptop. The laptop is running Windows 7 Professional.

I noticed I turned on/off the tube light and the laptop makes device connected sound and device manager refreshes its device list by shrinking and expanding the list.

My laptop does not have a battery but I remember even when there was battery inside the laptop it still behaved same.

What is going on here? I do not want this to happen to because recently my OS got corrupted too (which I have fixed by reinstalling Windows) which resulted in communication via USB ports failing. And I believe that the real cause was this problem which I mentioned above that computer feels some device is attached when I turn on the light in the room..

UPDATE: I had my USB mouse connected to the laptop. I observed that when I switch on the tube light the USB mouse red light would go OFF/ON (happens with all USB ports I tested one by one) now why this happens I have no idea. My other laptop which is plugged in the same extension does not have such behavior.

What I have done now is that I have grounded the power extension properly and it seems to have solved the problem now. But I would like to understand why it really happened what has grounding to do with it ?

UPDATE 2: Grounding has not solved I was too quick to post the update earlier, no it has resolved nothing...it is behaving the same..

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  • Is your question "why does this happen?", "how can I disable this behavior?", or something else?
    – user530873
    Commented Oct 25, 2015 at 19:51
  • I have updated my question by adding more details in the last para
    – Ahmed
    Commented Oct 25, 2015 at 20:13
  • I'd try unplugging everything connected to the laptop but power, and plugging them in one by one. Almost sounds like something is acting as an antenna.
    – Journeyman Geek ♦
    Commented Oct 25, 2015 at 23:35
  • I get a similar effect with an old Palm device. I shut it off and plug it into a cradle to charge it (no signal connection, just power). The only wireless interface on it is Bluetooth, and that is shut off. However, If I switch my fluorescent desk lamp on, the Palm turns on. Both are plugged into the same wall outlet. Apparently, computing devices can be haunted.
    – fixer1234
    Commented Oct 26, 2015 at 0:20
  • Can a fluorescent put off enough of a interfering field to trigger a minor current? I know office lights require a ballast but I don't know what that means in general, only that they can hum like a tired old transformer when they're no good.
    – Radhil
    Commented Oct 26, 2015 at 1:52

2 Answers 2

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Many electrical devices can cause voltage spikes on the mains, transient electromagnetic fields, or both, when they are switched on or off - especially anything that contains an inductor such as the windings of a motor, a transformer, or the magnetic ballast found in older fluorescent lights. It sounds as if one of these effects is causing a brief dip or spike in your laptop's internal power rails, or an interfering signal on a data communication bus, which makes it think that a device has been disconnected. Of the two effects I'd suspect a power dip or spike on the mains would be more likely than the electromagnetic route. If you have a working battery you can check which is the culprit by seeing whether the effect still occurs when the laptop is running on battery and not connected to its adapter.

You should definitely ensure that all appliances are properly grounded if they are designed to require a ground connection - for electrical safety if nothing else.

Other things you could try include:

  • replacing the laptop's battery, which should help to protect against power supply variations
  • moving the laptop somewhere else in the room
  • plugging the laptop into a different outlet, if there is more than one
  • powering the laptop's mains adapter via a surge protector, 'mains conditioner' or even an online UPS
  • asking an electrician to check the light and perhaps replace the old magnetic ballast, if it uses one, with newer electronic control gear - this should also reduce flickering or buzzing

It sounds like something you should try and resolve, as the same effect could be causing data corruption if it happens while your laptop is writing data to disk, for example.

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Are these "smart lights" of any kind? I can't think of any reason why turning on lights would show up as a device on a computer, or even a reason a lightbulb could give a wireless output. Does the switch turn on a port or is it directly connected to only the light. If it is connected to a port there could be some wireless device connected and that's what is showing up on your computer.

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  • I have updated the question, properly grounding the power extension has solved it, but I wonder why only one particular laptop would suffer and not the other ones.
    – Ahmed
    Commented Oct 26, 2015 at 8:19
  • @Ahmed that is very strange.
    – Matthew Gilbert
    Commented Oct 26, 2015 at 15:51

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