Diagnostic Tree: Weird Lights
Strange Circuit Behavior in Your Home
If you have reached this page without beginning at the Start of the diagnostic tree, you may do better to start there.
If about half the lights of the home are dead but will come on quite dimly at times, especially when an appliance is run, most likely a main hot wire is open -- at the panel, main breaker, meter, or the power company's line. I have found this to be more often outdoors in the power company's domain, so I recommend they be called. If you want to learn more about the main open hot and to consider whether it might be occurring in your domain, see my page on Main opens, especially the paragraph where I talk about Sub-main breakers.
If at times some lights run dim and others bright, for several seconds or even minutes at a time, this is an open neutral -- of the main neutral (of power company, meter area, or within the panel) or else of a circuit neutral. It is probably the Main neutral if most of the home is affected in this way; because this is often a power company problem and because damage to electronics can be occurring, I recommend you call the power company before an electrician. If these symptoms are limited to one or two circuits, then the open neutral is probably one that is shared by Two circuits, in which case locate the trouble-point as an Open, watching for (and watching out for!) two circuits in any given box; damage can likewise occur to items running on these two circuits.