Mastering the Clock: How Long Should You Leave Grow Lights On?

One of the most common mistakes beginners make is leaving their lights on 24/7,
thinking „more light equals more growth.“ Unfortunately, plants are not
machines—they need sleep just like we do.
The Importance of the Dark Cycle
During the day (lights on), plants perform photosynthesis, accumulating energy.
During the night (lights off), they respire and break down that energy to fuel growth.
Without a dark period, plants can become stressed, stunted, or develop leaf issues.
Recommended Light Schedules:
Seedlings and Clones: These babies need plenty of energy. A cycle of 18 hours on /
6 hours off is standard to encourage rapid root and leaf development.

Vegetative Stage (Leafy Greens/Herbs): For lettuce, basil, or the vegetative phase of
larger plants, keep the lights on for 16 to 18 hours a day.
Flowering Stage: If you are growing fruiting plants (like tomatoes, peppers, or
flowers), you need to mimic the shorter days of autumn to trigger blooming. Switch
your timer to 12 hours on / 12 hours off.
Pro Tip: Always use an automatic timer. Consistency is key; turning the lights on at 8
AM one day and 11 AM the next will confuse your plants and lower your yield.