I've noticed it a few times now. When I first turn on the hallway light it has some minor flickering for 2-4 seconds and then stops. If I turn the light off and back on it does not do it it seems to only be when I turn it on from a cold start. Recently a lot of more lights were added to this circuit but they were not on at the time of this but could that still have something to do with it?
* The first time I saw it I changed out the light bulb but that didn't help.
The switch could be wearing out, including for such reasons as old age.
A typical light switch will handle several light bulbs.
When installing a new switch, wrap the wires around the screw terminals to attach them. Don't use the push in holes in back unless a screw is provided and absolutely needed to hold the wires in place back there.
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Is it a fluorescent light or incandescent? If it's a fluorescent theres little you can do. (In some instances "older models" a starter will be present in the fixture. You could try replacing that). Replacing the fixture is the only other option.
If it's an incandescent, tighten or replace the bulb.