How Close Should Grow Lights Be to Plants?

A well-designed lighting system is the most essential aspect of any indoor farming environment. Growers need to make sure their plants receive enough energy to develop at optimum rates without being overpowered. This leads us to one of our most frequently asked questions: how close should grow lights be to plants?

We’re afraid there’s no exact answer, as although grow light distance charts are readily available, the solution that’s right for you will ultimately depend on what type of lighting you use and which species you are growing. Most modern-day indoor farmers are ditching outdated HID (high-intensity discharge), and fluorescent T5 grow lights in favor of LED (light-emitting diode) lighting. 

With that in mind, let’s take a look at some considerations for LED grow light height, and dive into recommendations for how you can achieve the maximum output levels for your crop using advanced LED lighting systems. 

LED Grow Light Distance: Considerations 

Before we get started, it’s important to have a basic understanding of how to measure the light that reaches your plants. These are the main technical terms you’ll come across:

Photosynthetic Active Radiation (PAR) – PAR is not a measurement; it’s simply a descriptor for the type of light needed to support photosynthesis in plants. Specifically, PAR refers to visible light with wavelengths of 400-700 nanometers (nm). 

Photosynthetic Photo Flux (PPF) – PPF is the total output of photons in the PAR range from the light. 

Photosynthetic Photon Flux Density (PPFD) – PPFD measures the amount of PAR that reaches and is absorbed by your plants. Different locations on each canopy can have different PAR readings. As a result, the answer to the question ‘how close should grow lights be to plants?’ can have variable answers. 

Micromoles (μmol) – Micromoles are the unit used to quantify PPFD and are measured per square meter per second. 

Now that you’re familiar with the terms for measuring light, we can look at some of the primary factors that affect grow light distances:

• LED vs. Traditional Lights – Different types vary in the heat energy they produce and the light spectrums they offer, meaning the optimum distance from the canopy is changeable. 
• Wattage – High wattage lights typically need to be placed further away from plant canopies to avoid damage, whereas lower wattage lights can be moved closer.
• Plant Stage – The best lighting configurations take account of plant vitality throughout the various stages of development, so this needs to be factored into grow light distance. Seedlings and flowering plants will have different optimum proximities, for example. 

We’ll dive into each of these considerations in more depth in the following sections. 

How are LED Lights Different? 

The advancement of LED light technology makes it easier for growers to create perfect indoor farming environments and achieve greater crop yields on shorter growing cycles. This, in turn, leads to increased revenue and higher profit margins. The boost in LED efficiency and the associated rise in popularity of LED solutions comes down to a few key factors:

• LEDs are high quality and combine low maintenance costs with minimal hassle. 
• LEDs have longer life spans than their traditional counterparts. Modern LEDs last for upwards of 50,000 hours, equating to nearly six years of continuous use (the latest LEDs can last up to twice this long). 
• LED solutions can generate the entire spectrum of visible light colors without the need for filters.
• Because LED lights emit both red & blue wavelengths, and every color of white in between, they are well suited to all stages of plant development.
• LED lights emit less heat than traditional HID lights, so they can be positioned closer to the canopy.
• LED lights naturally emit light over a 180-degree angle, reducing waste and the costs associated with redirecting and reflecting light from 360-degree bulbs. 
• The cost of LED lighting solutions has been gradually decreasing for over a decade. Data from the Department of Energy data suggests LEDs prices have dropped by 90 percent since 2008. 

For these reasons, LED lighting is becoming the most practical and energy-efficient lighting solution for indoor farmers globally. Other industries are catching on too, and it’s estimated that over 87% of all light sources will be LEDs by 2030. 

How Does Wattage Affect Grow Distance? 

Wattage is considered a significant factor in determining how close grow lights should be to plants. In general, the higher the wattage, the further away from your plants the bulb needs to be. However, with LEDs, you can place them much closer to the plant’s canopy without causing any harm to the growing process. 

As an unofficial rule of thumb, many growers work on the basis that:

• You need 20-40 watts of power per square foot. 
• Lower wattage LEDs of around 200 watts should sit between 12-20 inches from the top of the plant.
• Higher wattage LEDs of 1000 watts and above should sit between 36-46 inches from the top of the plant.
• Medium wattage bulbs should sit between these ranges and be constantly adjusted to suit the light exposure needs of each species as they develop through the different stages of growth.

However, these guidelines are not a one size fits all solution. For instance, multi-bar or spider style lights can be hung at 12″ even when they are 600w lights. Scynce LED, in particular, uses secondary optics that allow us to get our 600w light (Raging Kush) within 6″ of the plants.

But there’s a bit more to it than that. It’s important to remember that wattage is simply a measurement of electricity. While it’s helpful for growers to keep track of wattage details, it’s not always a good idea to make decisions purely on electrical power when determining the amount of energy your plants need to grow. The primary reason for this is that often, it is the color spectrum in a bulb or LED chip, not the wattage, that determines the growth and vitality of a plant’s foliage and flowers.

Let’s cast our minds back to the definitions we ran through earlier. By adjusting the intensity and duration of plant exposure to PAR (visible light with wavelengths of 400-700nm), farmers should be able to optimize growth. So while you can find no shortage of led grow light distance charts online, there’s no universal answer to how close your LED lights should be to your plants based on wattage alone because you want optimum PPFD readings for every stage of each plant’s development. 

Ultimately, the health of your plants is more important than the strength of the LED bulb, so the best distances for light placement cannot be determined accurately without considering their needs throughout every stage of their life cycle. 

How Does Plant Stage Affect Grow Distance? 

As your plants develop, you may need to adjust the LED grow light height to account for both the upward growth of the plants themselves and their changing requirements for light intensity. However, plenty of growers leave their lights at a set height, preferring to adjust the intensity to meet the PPFD needs at the canopy level during each stage of growth. 

Plant growth is typically divided into three stages:

• Seedling
• Vegetative
• Flowering 

But how close should grow lights be to plants in each stage to get the healthiest crop?

As your plants progress between each phase, you’ll need to continually reduce your LED grow light distance. Seedlings need the least amount of light intensity, so at this point, your lights need to be at their highest above the plant canopies. Alternatively, you can also lower your lights and turn down their intensity instead of moving their placement. Traditional lights (HID or CMH) can usually only go down to about 50% intensity. However, Scyne LED lights can go down to 10%. 

In the vegetative stage, more intense light is required for optimum growth. And when your plant’s flower, you’ll need to move your lights closer again to provide them with higher levels of PAR for photosynthesis. 

Seedlings

If the soil is dry, then a seedling will never reach its full potential, which is why your LED lights should be higher above the canopy at the start of the growth cycle. Seedlings are sensitive and vulnerable, and while it can sometimes be tempting to expose them to a short burst of high-intensity light to stimulate rapid growth, this is not recommended. Until the plants become more mature, there is no need for higher light intensities, so growers need to be patient to get the best results. 

So, exactly how close should grow lights be to seedlings? Here is a guideline:

• 1000W – Up to 46 Inches
• 800W – Up to 42 Inches
• 600W – Up to 38 Inches
• 400W – Up to 27 Inches
• 200W – Up to 20 Inches

Vegetative 

In the vegetative stage of development, when plants are maturing, the light spectrum requirements remain similar to those of seedlings. However, to develop healthy roots and stems that will lead to a good yield, the light intensity should be increased to ensure plants have more energy to photosynthesize. Even if you are regulating light proximity by trial and error, the advantage of LED lights is that they emit very low levels of infrared radiation. So the risk of light burn is minimal, even if you don’t get it quite right on the first attempt.  

So, how far should LED grow lights be from plants in the vegetative stage? Most LED light distance charts typically recommend the following ranges:

• 1000W – Between 36 and 46 Inches
• 800W – Between 32 and 42 Inches
• 600W – Between 30 and 38 Inches
• 400W – Between 20 and 27 Inches
• 200W – Between 12 and 20 Inches

Flowering

In this final stage of the life cycle, plants need the highest light intensity levels to support continued stem growth, blooms, and flowers. So growers need to move their LED lighting systems even closer to the canopies. For the best results, this is best done gradually to give plants the time they need to adapt. So lower your system slowly and constantly monitor for signs of distress until you reach the optimum light distance from your plants. Charts typically recommend you stay within the following parameters:

• 1000W – Between 21 and 36 Inches
• 800W – Between 19 and 34 Inches
• 600W – Between 18 and 30 Inches
• 400W – Between 13 and 21 Inches
• 200W – Between 8 and 16 Inches

Signs Your Light is Too Close to Your Plants

While increasing light intensity throughout a plant’s lifetime is necessary to facilitate healthy growth, you’ll need to observe your plants carefully to ensure you have not moved your LED lights too low too quickly. Look out for the following telltale signs of distress:

• Irregular or stunted growth – Usually characterized by leaves becoming limp, curly, or dropping.
• Bleaching – Typically indicated by white or yellow spots on the highest leaves.
• Burning – This normally starts with thin brown outlines on the leaves closest to the light before discoloration of larger sections becomes apparent. Keep in mind, what sometimes looks like light burn may actually be nutrient burn. 

Signs Your Light Is Too Far From Your Plants

Leaving your lights too far from your plants will leave them looking stretched and weak, and if not rectified, this will lead to color loss and death. It can sometimes be easy to confuse the signs of underlighting with accelerated growth because plants that are deprived of light will naturally grow upwards at a faster rate. However, this process, known as etiolation, is not a good sign. It is the defense mechanism of a plant reaching for more light in a bid to photosynthesize. 

Optimize Your Crop with Scynce LED Technology

The team at Scynce LED has developed a new breed of LED light penetration technology that enhances growth from root to canopy. Our patented optical software directs precisely the right amount of energy to your plants by consistently delivering even and deep penetrating light. 

With Scynce LED, you’ll have complete control over every plant as you can adjust your facility’s light recipes and grow schedules remotely from your smartphone, tablet, or computer. So you can set, forget, or keep tweaking as you see fit – and never need to worry about grow light distances again!

Contact us today to learn more about the next generation of LED greenhouse lighting solutions and how we can help maximize your yield.