Grow Light Height Above Plants

By Charlie Pearson

What are the Best Practices When considering Grow Light Height Above Plants?

So, you've got your grow lights, your plants, and your hydroponic system is ready to go. You put the grow lights in place and turn them on, excited to start growing your plants. But before you flip that switch, you should consider how high your grow lights need to be above plants.

Grow light height above plants is really important, and it depends on the type of lights you have. Hanging your lights too low can burn your plants, but hanging them too high can mean you aren't providing your plants with enough light. I'd suggest following the height recommendations provided by the light manufacturer. However, if that information isn't provided, you can find recommendations for different types of grow lights below.

As mentioned previously, grow light height above plants depends on what type of grow lights you have. Some lights produce more heat while others run cooler, and each needs to be hung at a different height from your plants. For example, LED grow lights need to be hung farther away from your plants than MH or HPS grow lights to avoid bleaching the canopy of your plants from strong spectrums. Fluorescent grow lights need to be hung closer to plants than MH/HPS grow lights in order to provide proper lighting because the light coming from fluorescent grow lights isn't strong enough to get plants growing when they're hung more than 12" (30 cm) away from your plants. Below you will find recommendations for grow light height above plants for different types of grow lights and wattages.

HID Grow Lights

HID grow lights include MH and HPS lights. They produce quite a lot of heat, so they'll need to be hung higher. With HID grow lights, it's best to keep them at least 12" (30cm) away from your plants at all times. The stronger the light, the further you'll need to hang it, so if you have a 1000-watt light you may want to hang it at least 16" (40cm) away. However, you won't want to hang your light higher than 30 inches (75cm) above your plants. Smaller lights, like 400-watt ones, should be 20" (50 cm) away from your plants, and medium-sized lights, like 600-watt ones, can be hung around 25" (63 cm) above your plants. To sum up, below are the recommendations for grow light height above plants for HID grow lights:

400W HID grow lights: 12-20" (30-50 cm) away from plants

600W HID grow lights: 14-24" (35-60 cm) away from plants

1000W HID grow lights: 16-30" (45-75 cm) away from plants

LED Grow Lights

Even though LED grow lights don't produce lots of heat like HID grow lights, their light spectrum can be overwhelming for some plants if they're hung too close. When this happens, your plants will suffer from light bleaching, which will impact how your plants take in light and convert it into energy for growth.

Considering you need to hang LED grow lights higher, it means they will cover a larger area, which makes them incredibly efficient. Small LED lights used to grow herbs (15-90W) need to be at least 16" (40 cm) away from your plants. Higher wattage lights need to be hung even higher. Below are recommendations for grow light height above plants for different wattages:

240-400W LED grow lights 16-30" (40-75 cm) away from plants

450-550W LED grow lights 20-30" (50-75 cm) away from plants

600-850W LED grow light 24-36" (60-90 cm) away from plants

900W+ LED grow light 26-42" (65-105 cm) away from plants

Fluorescent Grow Lights

Fluorescent grow lights produce little heat, but the light they produce is not as strong as the light produced by HIDs or LEDs, so you'll need to hang them quite close to your plants. What makes hanging fluorescent lights a bit tricky is that not all of them are the same. CFL bulbs can generate quite a bit of heat over an extended period of time because of their compact size, whereas a longer T5 grow light won't generate lots of heat because it can dissipate it along its tube. Not only that, but the more bulbs you use, the more heat they will produce, which can be dangerous if they're hung too close to plants. In general, fluorescent grow lights should be hung no more than 12" (30 cm) away from your plants.