How long should fluorescent grow lights remain on daily?
Written by
Benjamin Miller
Reviewed by
Prof. Charles Hartman, Ph.D.Daily timing with adequate light duration is critical to the growth and development of plants under fluorescent grow lights. The requirements for daily light duration can vary significantly depending on the type of plant and its stage of growth. Having the correct light timing ensures that growth does not prematurely flower and maximizes photosynthetic efficiency. I consistently check my timers throughout different seasons. Getting the right timing can make all the difference in quality and quantity at harvest time.
Seedlings require a relatively long period of exposure to light each day. Sixteen hours is ideal, as seedlings establish a strong root system, avoid stretching, and produce thicker stems with optimal light levels for this length of time. I start counting when the first true leaves appear. Overall, this light duration replicates long summer days, ensuring that the seedlings receive adequate establishment.
Timer Precision
- Use digital timers with 1-minute accuracy
- Program gradual sunrise/sunset simulations
- Avoid abrupt light transitions stressing plants
Seasonal Adjustments
- Increase duration by 2 hours in winter months
- Reduce by 1 hour during peak summer heat
- Align with natural daylight extension patterns
Growth Monitoring
- Track stem elongation rates weekly
- Document leaf expansion patterns
- Record flowering response times
Leafy greens flourish with 14 hours of daily exposure to get the growth they want. This prevents lettuce from bolting early and guarantees a good density of leaves. Spinach grows thicker leaves on a 14-hour schedule. I stay at that amount of time from transplant to harvest. The dark period serves the important physiological functions of metabolism.
Herbs do best with 14-16 hours of light, depending on the type. Basil, for example, ramps up flavor intensity at 16 hours, while mint will thrive well at 14 hours for a typical market or culinary quality. The same applies to the oil concentration test. My Genovese basil receives the most daylight. It is also important to keep an eye out for signs of light stress, such as curling leaves, as you approach the maximum number of hours of light.
Utilize energy conservation practices utilizing prolonged photoperiods. Set your lighting for the utility's off-peak time. Use reflective surfaces to maximize light penetration. I save 30% on my electric bill by utilizing selective times. Your plants receive sufficient light while offering significant savings on expenses.
Read the full article: Fluorescent Grow Lights: Expert Guide
