How Close Should Grow Lights be to Plants?

How Close Should Grow Lights be to Plants?

Lots of us know about the grow lights used to supplement natural light for the plants that are grown inside. But there is some confusion on how close should we place them to our plants. Keep reading to learn more about how close should grow lights be to plants!

Got more questions about grow lights? In other posts, we talk about how long to leave grow lights on, and the best grow lights for small spaces. For a full list of resources, check out our indoor plant guides for more info!

Grow Lights: A General Rule of Thumb

The simple answer is to keep them 12-30 inches away from the top of plants. Change the distance between the plant and light gradually as the plant develops. The distance also depends on the type of plant you are growing, stage of the plant, type, and power of light you are using.

How should we vary the distance?

As mentioned, its a general rule of thumb to place grow lights between ranges of 12-30 inches above the plant foliage. The exact distance depends on the following variables.

1: Stage of Plant Growth

Seedling stage:

At the stage of seedling foliage of the plant is very soft and delicate so the high intensity of a grow light can be harmful to them. A gentle, lower intensity of light is good for the seedling. The average distance recommended for seedling is between 24-35 inches from the light and top of the plant. This recommendation also changes slightly with different types and the power of light being used.

Flowering stage:

During the flowering stage, the plant is fully grown so its requirement is changed. The height of the light is raised as compared to the seedling stage. The average height is 16-36 inches from plant top foliage to the light. If you move the light closer it will increase the photosynthesis but it is harmful and more dangerous for the plant.

2: Power or Wattage of Grow Light

The following table will help you in defining the distance between your plant and light.

Sr noWatt or power of lightHeight between top of plant foliage and light
1200-39912-20 inches
2400-59920-27 inches
3600-79930-38 inches
4800-99932-42 inches
5More than 100036-46 inches

3: Type of Grow Light

Metal Halide & HPS Grow Lights:

  • Metal Halide & HPS Lights are the type that is used widely because they produce high yields in cannabis.
  • These lights work amazing for the plants in the vegetative stage.
  • The distance between the plant’s top and light depends on the size or watt of the lamp.

LEC/CMH Grow Lights:

  • The LEC stands “Light Emitting Ceramic” and CMH stands “Ceramic Metal Halide”.
  • The distance from the top of the plant to the light varies. 315 LEC and 315 CMH are their popular size.
  • In 315 LEC and CMH keep the distance of about at least 18 inches. Whereas some models required 3 feet distance.

LED Grow Lights:

  • LED light is wonderful if used correctly. They are powerful and give high yield
  • The distance between the lights and plants varies from model to model.

Fluorescent Grow Lights (like CFLs & T5s):

  • Fluorescent lights are not too hot so it is not recommended to grow cannabis below these lights.
  • These lights don’t cause light burn to the plant.
  • The distance between the plant and light can be measured by the general rule of ‘’hand test’’. Keep your hand below the light for 30 seconds where you wish to place the plant. If you don’t feel too much heat then the place is perfect for your plant.
  • For the best results from these lights, it is recommended that daily check the light intensity and replace them if you feel less heat.

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