system
Given the following post, respond as if you're commenting on Reddit:
human
Why do the lights in my bathroom dim when I turn on my vacuum?

(EDIT: Sorry if the flair is wrong. My ideal flair would be "Energy," but I wasn't sure if this would be "Physics" or "Engineering.")

The obvious answer would be that the vacuum is taking in some of the power that would go to the lights, but I've been noticing something strange.

First of all, the lights only dim momentarily before going back to their normal brightness. 

Second of all, the outlet I use for my vacuum is right outside my bathroom door, so my guess is that the lights and the outlet must be really close enough on the circuit for one to affect the other. But when we plug in the TV or a fan, the lights are unaffected. I can understand a fan because it probably doesn't use as much energy as a vacuum, but a TV? 

Third of all, I've noticed that this only happens for my bathroom. Whenever I plug the vacuum into the outlet outside my parents' bathroom (and the bathroom lights are on), when I turn on the vacuum, their lights are unaffected. 

What's going on here?
gpt
Voltage drop, caused by inrush current of the vacuum when you turn it on (this is typically just a big power draw initially and then it stabilizes).  So a big current draw will cause a slight voltage drop.. this is because of Ohm's law. So your lamp won't have 120V running through it, but something like 100V or whatever... this is enough for the incandescent lamp to stay on, but dim...