Indoor plant growers want to know how far grow lights need to be from plants so they don’t burn or suffer.
The answer is, the distance varies based on the age of the plant and the type and wattage of the grow lights used.
In this article, I’ve outlined the recommended distances for fluorescent, LED, and HID lights at each stage of plant growth. I’ll also touch on why it’s important to get this right so that my plants can be as healthy as I hope for.
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Different Heights for Different Grow Lights and Wattages
LED Grow Light Bulb Distances
My LED (light-emitting diode) lights should be about 12-30 inches apart from the top part of my plants.
The nice thing about LED lighting is that they give me a little leeway in terms of distance because they let off relatively less heat.
In a study by Oklahoma State University, I learned that LED lights have the highest efficiency and lowest energy consumption in comparison to HID, fluorescent, and incandescent lights.
LED Distances by Wattage:
- 1000w or more LEDs sit 36-46 inches away
- 800-900w LEDs sit 32-42 inches away
- 600-799w LEDs sit 30-38 inches away
- 400-599w LEDs sit 20-27 inches away
- 200-399w LEDs sit 12-20 inches away
Fluorescent Light Distances
I never raise fluorescent grow lights more than 1 foot above my plants because they won’t be effective at that height. Five inches is a good light distance to start with.
These lights aren’t quite as strong as the others, but I do recommend keeping an eye on them in case their heat emission does burn the plants.
HID Grow Light Distances
My HID (high light intensity discharge) lights should be a minimum of 12 inches apart from any part of my plant in any case.
There are differing strengths of HIDs based on their sizes, but the lights shouldn’t go more than a maximum of 30 inches away.
You should also read: Are Grow Lights Bad For Your Eyes?
Flowering Plants Distancing
The distances to keep grow lights from my flowering plants will be slightly different, based on their growth stages. The following guidelines go solely for LED lights.
1. Seedling Stage
To keep my seedlings from drying out, I will make sure LED grow lights are no further than 24 inches (and no more than 36 inches away).
2. Vegetative Stage
When the plant is past seedling age but not yet flowering, I can optimize its growth by placing my LED lights or grow lamp closer than they were in the seedling stage.
However, I don’t want to place them too close, as this stage is when the maturing happens. I don’t want to stunt its growth with excess heat that could come from putting the lights too close.
3. Flowering Stage
Note that for LED grow lights, the distance must get shortened in the flowering stage. This helps optimize photosynthesis.
I will make sure my grow lights are 16-36 inches from the plant canopy in this vital flowering phase.
Frequently Asked Questions
Here are the most common questions people have when it comes to distancing.
Is too much light bad?
Too much light is bad because it can lead to bleaching or drying out of plants. If my plants get too dry, they won’t have enough water to fuel the photosynthesis process.
How can I tell if a grow light is too close?
While the obvious sign is a dried out plant, it’s better to know before the plant dies. I can tell if a grow light is too close to a plant based on several factors – the stage of plant growth, the type of grow light I’m using, and the wattage of my grow light. Each of these factors work relative to each other.
Can an LED grow light burn plants?
Yes, it’s possible for LED grow lights to burn my plants. However, LED are far less likely to output enough heat to do so in comparison to HID and fluorescent lights.
Where should I locate my grow lights for plant growth?
Grow lights are best placed above the canopy of my plants (the canopy is the top layer of leaves). If my plant hasn’t sprouted yet, I can place the light above the top of the soil instead
Placing grow lights at the best distance above my plants is easy enough if I know what type of light I’m using, as well as its wattage power. Additionally, it will help me to know how far along the plant is in its harvest cycle (seedling, vegetative, or flowering stage).
In general, though, I can count on LED lights as being the least heat-destructive to my plants and the most trusted artificial light. They are also the most energy efficient grow lights, and I can place them closer to my plants in general than I can place HID and fluorescent grow lights.
Further reading: Can You Leave Grow Lights On All Day?