One flickering bulb may simply be loose or failing, but several lights fluctuating together can point to a connection or supply problem. The scope of the flicker is the first clue for deciding what can be checked safely.
If it is one fixture, start with the bulb
Turn the fixture off, let it cool, and confirm the bulb is compatible and seated properly. With LEDs, an incompatible dimmer can also cause flicker even when the wiring itself is sound.
If it happens when an appliance starts, note how severe it is
A very brief dip when a large motor starts can occur, but strong or repeated flicker with ordinary appliances deserves investigation. Do not install larger fuses or breakers to hide the symptom.
Multiple rooms mean a wider problem
If lights on different circuits change brightness, go out, or some become brighter while others dim, a service or connection issue may be present. Do not open the electrical panel to investigate it yourself.
Heat, burning odor, or arcing means stop
Turn the circuit off only if that can be done from a normal safe control, stop using the affected area, and call an electrician. If there is smoke or fire, leave and contact emergency services.
Sources
- U.S. Consumer Product Safety Commission — Electrical Safety — Household electrical hazards, receptacles, switches, wiring, and safe response to overheating.