Light fixtures flicker after replacement
The power feed to a single phase fixture can be connected either way. The fixture doesn't care or at least I have never seen one that does.

Are these fluorescent fixtures? The flickering could mean you didn't seat the lamps well enough into their sockets. The pins should go straight in and then twist the lamp ¼ turn to seat them firmly.

They should flicker slightly when they are brand new and first turned on but the tubes will "burn-in" in just a few hours. Leave the lights on for a couple hours to allow them to burn in and they should stop flickering or strobing.

Otherwise they flicker slightly as the are turned on anyway depending on the type of starter in the fixture. This should only be a split second though and they should come up to full brightness.

Happy Friday!