Accidental dark period

I leave the lights on 24 hours a day to encourage maximum growth. Recently the lights were left off for 18 hours. The light is back on continuously. Will that 18 hours without light effect my plants?
Mr Mayhem,
Warren, Ohio

Leaving the lights off for one 18-hour period will have no significant effect on the plants. They will continue to grow vegetatively and will lose only 18 hours of photosynthesis so their growth is set back a little less than a day.

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