Is it acceptable to attach a 14 gauge light in a 12 gauge 20 amp circuit? I am finishing my basement and using 12 gauge wire throughout. When I bought my light fixtures, they are wire with 14 gauge wire. Is it safe to use these or do I need to get different light fixtures?

Yes, you can use those lights, most light fixtures come with 16 or 18 gauge wire.

Whatever wire came installed inside the fixture is acceptable to be used on a 15 or 20 amp circuit. Since it only will carry the current that the fixture will draw it may be much smaller than the wiring on the supply circuit. Most fluorescent fixtures have 18 gauge wire internally and yet I hook them to #12 wiring all the time.

Thank you for the answers. Very helpful.