Lights in a house can become dim because major appliances are pulling too much electricity from the same electrical circuit as the lights. Other causes of lights dimming include neighborhood-wide problems with the power grid or serious issues with the house's electrical panel.
If lights in a house go dim when a major appliance is running, or if several are running at the same time, the lights that have dimmed are possibly on the same electrical circuit as the appliances. In this case, the problem may be an overloaded circuit. This occurs most often in older homes that are not wired to handle large numbers of appliances.
If the entire neighborhood is experiencing dim lights or power outages, there is probably a problem with the electricity coming into the house. The problem could be at the nearest transformer or even at the local substation. This can occur during bad weather or when there is an unexpectedly high demand for electricity. In this case, simply waiting for the power grid problems to be resolved is the only thing that can be done.
If random lights flicker throughout the house and the dimming is not tied to appliance usage, there could be a serious problem with the electrical panel or meter. If service conductors in the main electrical panel become loose, they create heat and can even burn up. This is a significant problem that must be handled by a licensed electrician.