What is the correct hanging height for my LED Grow Light?

How High?

When it comes to growing plants with LED grow lights, determining the correct hanging height is a common concern for many cultivators. If the light is hung too high, the plant will not be able to absorb enough light, leading to weak growth. On the other hand, if an LED grow light is hung too close, it can stress out the plants and is likely to cause light burn. To ensure that plants receive the optimal amount of light for growth, it's important to pay attention to three key factors: leaf surface temperature, PPFD, and the growth stage of the plants.

How Hot?

Leaf surface temperature is the first thing to consider. Most plants will not be burned if the leaf surface temperature does not exceed 29 degrees Celsius. While keeping the leaf surface temperature under control, the LED grow light can be hung as close to the plants as possible to increase the utilization rate of the LED grow light fixture and allow the plants to absorb enough light.

Mind Your PPFD

The second factor to consider is PPFD (Photosynthetic Photon Flux Density), which measures the amount of light (PAR) a plant receives over time. Adjusting the hanging height of the LED grow light is a way to change the PPFD that the plant can receive. Typically, the minimum PPFD value required for plant growth is 400μmol/ m ²/ s, while the maximum PPFD value that can be absorbed is 1200μmol/ m ²/ s. Anything exceeding 1200μmol/ m ²/ s will not be absorbed by the plants. As a result, growers should ensure that the PPFD value that the plant can absorb is over 400μmol/ m ²/ s and not too high, as excessive PPFD will be lost. LED grow light suppliers often provide PPFD maps for reference, and it's best to have a PAR meter to measure PPFD values. Adjusting the hanging height according to the PPFD map or the actual measured PPFD ensures that the surface temperature of the leaves does not exceed 29 ℃ and all plants can receive the highest possible PPFD.

Little By Little

The final factor to consider is the growth stage of the plants. Typically, plant growth is divided into three phases: seedling stage, veg stage, and blooming stage. Each stage requires different PPFD values, with the seedling stage requiring 400μmol/ m ²/ s, the veg stage requiring 400-800μmol/ m ²/ s, and the blooming stage requiring 800-1200μmol/ m ²/ s. The hanging height can be adjusted according to each growth stage to ensure that the plants receive the right amount of light.

Green is good. 

If you notice yellowing in your plants, it's a sign that they are getting light burned, so you should reduce the power and raise the LED grow light accordingly. A healthy plant should be a rich, dark green. If you notice that your plants are a more yellow shade of green, it is likely that they are becoming light-burned. Light burn occurs when your plants are given more light than they can handle. Think of it as sunburn for your plants. Light burning is perhaps the most common mistake made by new LED grow light users. Monitor the colour of your plants daily. Remember, you can always increase the light if you need to, but once plants are light-burned it can be very hard for them to recover from this. So a wise grower will work under the ethos of "less is more".

In summary, there really is no one-size-fits-all answer to the question of how far your LED grow light should hang from your plants. It's important to consider the leaf surface temperature, PPFD, and growth stage, and adjust the height accordingly. Many indoor growers hang their LED grow lights between 10-20 inches from the plants. With advances in technology, many LED grow lights now have a dimming feature, allowing growers to adjust the brightness according to the growth stage and save electricity. By paying attention to these factors and monitoring the colour of your plants, you can grow healthy and productive plants with high returns.