If your lights dim momentarily when an appliance such as an air conditioner, washing machine, furnace, or refrigerator comes on, it may be that the lights are wired on the same circuit as that appliance. You can easily verify it by turning off the circuit breaker associated with that appliance and see if the dimming light also turns off. This is not necessarily a dangerous scenario, but if you’re worried about it, it would be worth a call to a licensed electrician to investigate. These types of appliances tend to draw a lot of power when they first turn on, which is why they are usually connected to a dedicated circuit in the service panel. Owners of older houses may find that these appliances are probably sharing circuits with other loads. If necessary, your electrician can install dedicated circuits for these devices to help alleviate the dimming problem.

If all the lights in your house dim periodically or all the time, or even get brighter and possibly burn out occasionally, the problem could either be with a loose or bad connection in your circuit breaker panel or electric meter, or with the utility line feeding your house. Many times, this type of problem is due to an overloaded utility transformer on the street. This happens over time as more houses are built in your neighborhood, thereby increasing the demand on the existing utility wiring. A quick call to your utility company repair department can dispatch a technician to see if the problem is on their lines. If the problem is not with the utility lines, then you’ll need a licensed electrician to check your service entrance equipment for problems. You should not ignore this symptom, as it may be a sign of a possibly dangerous problem.

One other cause of dimming lights in your house could be due to an undersized service. This is usually more of a problem with an older home than one built in the last 20 or 30 years. Houses older than this (and especially house with fuse boxes instead of circuit breakers) do not supply enough electrical current to power the appliances and other technology that we all have in our homes today. Again, if this is the problem you’re experiencing, then an electrician can perform a service upgrade, which will bring enough power into your house to handle all of your needs for the foreseeable future.