Reason #1: The Light Bulb is Loose
To Fix: Thread the bulb tighter.
Reason #2: The Socket is Bad
Light bulb sockets make contact in two places and can corrode over time—especially in outdoor fixtures. If it wears overtime or something else happens to it, the lightbulb won’t function properly and that could result in it flickering. To Fix: With the switch powered off, check and see if the socket is in good condition. If not, it will probably need to be replaced.
Reason #3: The Switch is Failing
The metal connections on the light switch may wear over time, or the one installed might be a defect and never had a properly made connection at all. To Fix: Replace the light switch and see if it works. You can swap the switch with one from another room that you know is working to see if it works in the room that’s flickering.
Reason #4: You Have LED Lights
Some of the newer LED bulbs simply aren’t compatible with older switches, particularly dimmers. To Fix: Try to figure out if the current dimmer switch is “LED compatible.” If not, replace it with one that is. Also, you can see if the LED light is a dimmable bulb.
Resources
Heath demonstrated a variety of light switches and fixtures, which can be found at any home center. In general, he recommends checking the switches to ensure they’re up•to•date and operating properly to troubleshoot any issues with flickering lights.