Optimal Distance: How Far Should Grow Lights Be from Plants?

One of the big questions, once you’ve purchased LED Grow Lights, or LED Lighting for Greenhouse Commercial Growing, is how to get them up and how far should they be away from the top of the canopy. Ideally, the lighting system should be able to move up as the plants grow to maintain an optimal height.

This post answers some of these basic questions

The Importance of Proper Lighting in Indoor Farming

A well-thought-out lighting system is crucial in any indoor growing setup. First and foremost, you should ensure the plants get the right amount of light for optimal growth. You should not overwhelm the plant with too much light. So determining the proper distance between the grow lights and the plants is key.

Before we start, here are some key grow light terms you should know:

Photosynthetic Active Radiation (PAR): This term describes the type of light that plants need for photosynthesis. It refers to light wavelengths between 400-700 nanometers (nm).

Photosynthetic Photo Flux (PPF): This is the total number of photons in the PAR range emitted by a light source.

Photosynthetic Photon Flux Density (PPFD): This measures how much PAR actually reaches and is absorbed by the plants. Different spots on the plant canopy may have varying PAR levels.

Micromoles (μmol): This is the unit used to quantify PPFD, measured per square meter per second.

Factors Affecting Grow Light Distance

There are several factors influence the optimal distance between grow lights and plants:

Type of Light: Traditional lights like High Pressure Sodium and fluorescents are being replaced by LEDs due to their efficiency and spectrum range. HID lights need further distance from the plant because of the heat they generate. With LEDs, this is much less of an issue.

Wattage: Higher-wattage lights generally need to be placed further away to prevent plant damage, while lower-wattage lights can be closer. However, go too low on the watts and you won’t have adequate PPF to do the job.

Stages of Plant Life: Different stages of plant growth require different light intensities and therefore different distances. Stages include, such as seedling, vegetative, and flowering.

Advantages of LED Lights

LED technology has revolutionized indoor farming by offering these benefits:

Quality and Durability: LEDs are long-lasting. This means lower maintenance costs as there won’t be bulbs and ballasts to replace.

Full Spectrum: LEDs can produce the entire spectrum of visible light. These include red and blue wavelengths. This makes them suitable for all plant growth stages.

Heat Emission: LEDs emit very little heat. You can place them closer to the plant canopy.

Cost-Effectiveness: The price of LEDs has been dropping. This makes them a more affordable option for growers.

Wattage and Distance Guidelines

Wattage plays a significant role in determining the distance between the lights and plants. It is one of the most important things to know about grow lights. As a general rule here are some guidelines:

400 Watt LED Grow Lights

Seedlings – max of 28 inches from canopy top.

Vegetative – Between 20 and 27 Inches from canopy top.

Flowering – Between 12 and 22 Inches from canopy top.

800 Watt LED Grow Lights

Seedlings – max of 44 inches from canopy top.

Vegetative – Between 31 and 43 Inches from canopy top.

Flowering – Between 18 and 35 Inches from canopy top

1000 Watt LED Grow Lights

Seedlings – max of 48 inches from canopy top.

Vegetative – Between 35 and 48 Inches from canopy top.

Flowering – Between 21 and 39 Inches from canopy top.

Note: These are general guidelines only. The starting points that work for you should be adjusted according to the specific needs of each plant species and growth stage.

Importance of Plant Stage and Light Distance

In general terms, the light intensity increases as the plant goes from seedling to flowering.

Seedlings: Require less light intensity and should have lights placed higher.

Vegetative Stage: Requires increased light intensity for healthy root and stem development.

Flowering Stage: Requires the highest light intensity levels for blooms and fruits.

Signs of Incorrect Light Placement

Be on the lookout for signs that your lights are too close or too far away:

Too Close: Look for limp, curly leaves, or white/yellow spots.

Too Far: Plants may appear stretched and weak, losing color and vitality.