Marijuana Lighting Guide Part II: Lighting During Growth

Your marijuana plants need varying types of light with varying intensities at different stages of growth.

In Part I, you learned about the various types of marijuana grow lights you can use. It’s important that you understand when to deploy the different lighting options for your marijuana plants. Some lights are better suited during the vegetative stage while others are more appropriate during the flowering stage. In this guide, we’ll explain both. We’ll also describe the lighting cycles you should follow while your marijuana plants grow. Finally, we’ll provide a few last lighting tips regarding how to set up your marijuana grow lights for the best effect.

Marijuana Lighting By Stage

Metal halide (MH) bulbs produce a large amount of light within the blue spectrum. That part of the spectrum is best used during your marijuana plants’ vegetative stage. Assuming your plants receive zero sunlight, use metal halide bulbs to provide the main source of light during this stage. Once your marijuana plants reach the flowering stage, switch to high press sodium (HPS) bulbs. The light they produce is within the orange-red spectrum and stimulates the hormones needed for budding.

If you use high press sodium bulbs during the vegetative stage, your plants will probably grow tall very quickly. But, they’ll be thin, so your harvest won’t be as plentiful. If you use metal halide bulbs through both the vegetative and flowering stages, your marijuana plants will take longer to grow, but the harvest will be bigger than otherwise. Ideally, you should use a combination of both types of bulbs during both the vegetative and flowering stages.

Marijuana Lighting Cycles

Your marijuana plants need varying amounts of light and darkness as they grow. During their vegetative stage, follow a cycle of 18 hours on (with light) and 6 hours off (in darkness). Your plants can grow with as few as 6 hours of light each day, but they need more to grow properly. Once your plants have reached the flowering stage, switch the lighting cycle to 12 hours on and 12 hours off.

While your plants are in their vegetative stage, you’ll need to supply 2,500 lumens for each square foot of your grow area. Once they reach their flowering stage, you’ll need to have approximately 10,000 lumens per square foot.

Final Marijuana Grow Light Tips:

- When your marijuana plants are in the dark part of their cycle, don’t interrupt them by exposing them to light. Doing so can disrupt their development.

- Build a fixture for your grow lights so they can be suspended above your marijuana plants and raised as your plants grow (to prevent the lights’ heat from harming your plants).

- Use reflectors or a wall surface that can reflect your marijuana grow lights. That will allow the light to engulf your plants from every direction.

- Remember, HIDs generate a lot of heat. Use fans to keep the temperature in your grow room to approximately 75 degrees Fahrenheit.

- Keep all flammable items safely away from your grow lights.