Flickering lights signal something is not quite right. It might be a simple problem. It also could be a symptom of a dangerous problem. Frequently, it is simply a device on the circuit pulling more power than the circuit can supply for a few moments.
If incandescent bulbs are loose in the sockets, the connection can be broken for a moment, causing flicker. A vibration as simple as walking across the floor can cause the problem.
Wires that were not twisted together properly may have poor connections. Vibrations cause the connection to momentarily break, causing flicker.
Incandescent lights that suddenly decrease in brightness for a moment or longer can indicate a heavy load on the circuit, such as a motor that has turned on. Refrigerators and washing machines are often culprits in homes with older wiring.
Sometimes pests like squirrels or rats can chew wire insulation, causing shorts in the wiring that make the lights flicker. This is a potentially dangerous problem.
A number of improper wiring issues can cause the lights to dim or flicker. These problems range from mildly annoying to potentially being fire hazards. Older aluminium wiring is often suspect and should be inspected.
Check and tighten all bulbs in their sockets. Ensure that circuits are not close to being overloaded. Consult a qualified electrician and have your home inspected for dangerous wiring problems.