Why Does Grow Light Distance Matter

Grow light distance is a critical factor in determining the optimal amount of light for plant growth. The distance between the grow or light source and the plant canopy directly affects light intensity, which in turn impacts photosynthesis, growth, and development. When the light is too far, plants may not receive enough light, leading to weak and leggy growth. Conversely, placing the light too close can result in bigger trouble.

Adverse Effects of Too Much Light

Too much light can have adverse effects on plant growth, including light burn, bleaching, and reduced yields. Light burn occurs when the plant receives too much intense light, causing damage to the leaves and reducing photosynthesis. This can result in scorched, crispy leaves that are unable to perform their essential functions.

Bleaching occurs when the plant receives excessive light, causing the plant leaves to become brown or yellow. This is a sign that the plant is stressed and unable to process the intense light.

Understanding the optimal grow light distance is essential for maximizing plant growth, preventing light burn, and minimizing energy consumption. By carefully adjusting the light distance, you can ensure that your plants receive the right amount of light to thrive, promoting healthy and vigorous growth.

Factors to Consider When Determining Grow Light Distance 

Hanging the grow light too high will throw away light, and hanging too close will hurt the plants, so how do you make the right decision on the distance of LED lighting from the herb plant?

Checking the Leaf Surface Temperature

Most of your plants will certainly not be burned if the leaf surface temperature stays below 29 degrees Celsius. As long as you make sure of that, you can hang the grow lights as close as feasible to your plants. This will not only increase the utilization of LED grow lights but likewise boost plants to soak up sufficient light to expand.

Checking the Grow Room Temperature and Humidity

The grow room temperature and humidity also play a role in determining the ideal grow light distance. High temperatures combined with heat from the lights can cause plants to overheat, necessitating an increase in light distance to avoid heat stress or burn. On the other hand, in cooler environments, the lights can be positioned closer to provide additional warmth.

Humidity also influences this decision. In high-humidity grow tents, plants lose less moisture through transpiration, allowing lights to be placed closer. Conversely, in low-humidity grow rooms, plants lose moisture more quickly, so increasing the light distance helps reduce heat stress and prevents dehydration. Maintaining optimal temperature and humidity levels is essential for determining the best light distance to promote healthy plant growth.

Measuring Light for Plants

PPFD (Photosynthetic Photon Change Density) gauges the amount of light (PAR) a plant obtains gradually. As a matter of fact, changing the grow light distance is to change the PPFD that the plant can get. Generally speaking, the minimum PPFD worth required for plant growth is 400μmol/m²/s, and the optimum PPFD value that can be absorbed by plants is 1200μmol/m²/s. Anything beyond that will possibly hurt your plants.

As a result, you should ensure that the PPFD value ranges from 400 to 1200μmol/m²/s. Typically, both HPS grow lights and LED grow lights suppliers will provide PPFD maps for reference, but it would be better if you have a par meter to determine PPFD values.

In addition to PPFD, measuring light for plants involves other metrics used to quantify light intensity. One of the key metrics to measure light for plants is Photosynthetically Active Radiation (PAR), which measures the amount of light that plants can use for photosynthesis. Another important factor is the Daily Light Integral (DLI), which measures the total amount of light that plants receive over a 24-hour period.

By understanding these metrics, growers can optimize their lighting setup to provide the right amount of light for their plants. Using tools like PAR meters and PPFD sensors, you can accurately measure light intensity and adjust your grow light distance accordingly to ensure optimal plant growth.

Identifying Plant Growth Stage 

The plant life cycle is typically divided into 3 phases, seedling, vegetative, and flowering stages. Different phases of the plant, especially flowering plants, call for different PPFD and specific growth light spectrum. While the specific light intensity required by different types of herbs varies, there’s an overall grow light distance chart LED based on the stages of plant growth.

Image source: bioslighting.com

Seedling stage: 400μmol/m²/s, with a full-spectrum LED grow light distance between 24-36 inches above the plant canopy

Vegetative stage: 400-800μmol/m²/s, with an LED grow light distance between 12-24 inches above the plant canopy

Flowering stage: 800-1200μmol/m²/s, with a full-spectrum LED grow light distance between 18-24 inches above the plant canopy

How to Determine the Optimal Grow Light Distance

With basic knowledge about the three factors that have an influence on both traditional grow lights and LED grow light distance, here, we’ll give a step-by-step tutorial on how to determine an ideal LED grow lights distance in real cases.

Step 1. Follow Recommended Distance Guidelines

LED grow light manufacturers often provide guidelines regarding the recommended distance between the lights and plants. These guidelines consider factors such as the light intensity produced by the specific LED lighting model and the plant species being cultivated. It is advisable to start with these recommended distances as a baseline for the initial setup.

As LED grow light manufacturers ourselves, we also prepare recommended full-spectrum LED grow light distance chart for different series. Check them out.

Along with manufacturer recommendations, it is crucial to take into account the specific light intensity requirements of the plants at different growth stages. The correct distance for your plants, for example, varies depending on whether you are using LED, HPS, or CFL lights, and it is essential to adjust the distance from seedlings to the canopy to optimize growth and prevent light stress. Some plants may require higher light intensity during the vegetative phase, while others may need more intense light during flowering or fruiting.

Step 2. Experimentation and Observation

To further fine-tune the distance between LED grow lights and plants, it is better to start with small-scale trials. This involves setting up a few plants at varying distances from the lights and observing their response to different light intensities. By measuring plant growth, vigor, and overall health, growers can identify the distance that yields the best results.

Throughout the cultivation process, it is essential to closely monitor the plant development. If signs of light stress, such as leaf burn or leaves curling up, are observed, it indicates that the light intensity may be too high or too low. Adjustments can be made by moving the lights closer or further away.

Step 3. Adjusting Distance During Plant Growth

As plants grow and develop more foliage, the lower leaves may receive less light due to shading and less under-canopy coverage. During low light periods, such as cloudy days or winter months with reduced daylight, it is advisable to move the LED grow lights closer to the plants. Or, a more effective approach is to add under-canopy supplemental lighting to serve as an additional lighting source for lower leaves.

Some indoor plant growing tricks help compensate for the decreased light intensity, for example, topping outdoor plants is one effective way to ensure adequate light penetration for lower parts of the plant.

By following this guideline, you can determine the optimal distance between LED grow lights and plants. This approach maximizes the benefits of LED grow lights, promotes vigorous growth, and enhances overall plant health and productivity.

Lighting Distance for Specific Plants

Different plants have different lighting requirements, and the optimal lighting distance varies depending on the type of plant. For example, weed plants require a higher light intensity than lettuce plants, and the optimal lighting distance is closer for weed plants. During the vegetative stage, they may thrive with a light distance of 18-24 inches, while during the flowering stage, the light distance for weed, may need to be reduced to 12-18 inches to provide higher light intensity.

By understanding the specific lighting requirements of each plant, growers can optimize their lighting setup to provide the right amount of light for optimal growth and development. Whether you’re growing herbs, tomatoes, or leafy greens, adjusting the light distance to match the needs of your plants will help you achieve the best possible results.

Verdict on Grow Light Distance 

To sum up, the preferred grow light distance ranges from 12-36 inches, depending on which stage of growth your plant is in. Importantly, you should fine-tune the distance to achieve the perfect balance of light intensity and coverage through experimentation and observation. 

FAQs about How Far Should LED Grow Lights Be from Plants

How far to hang a fluorescent grow light?

There are three main types of fluorescent grow lights: T5, T12, and Compact Fluorescent Lamps. For young plants, starting at a height of 6-12 inches is ideal since they require higher light intensity. As the plants grow from the vegetative stage to flowering, increasing the distance to about 12-16 inches is recommended. When using T5 grow lights, it's generally best to position them as close as possible while keeping an eye on overheating or drying out.

What is the best distance for HID or HPS grow light?

HID grow lights, such as Metal Halide (MH) and High Pressure Sodium (HPS), produce more heat than LEDs but are affordable and commonly used for both vegetative and flowering stages. To determine the ideal distance from plants, a hand test can be done: place your hand above the plant canopy for 30 seconds—if it becomes uncomfortably hot, increase the light’s distance.

For 1000W HID lights, starting at a height of 19-26 inches is typical, and the lights can be moved closer as needed. However, it's important to avoid heat burn, which can damage plants, and ensure proper ventilation due to the heat output of HID lamps.

How far can grow lights reach?

The reach of grow lights, including how far LED grow lights go, depends on their specific design and the angle of light dispersion. LED grow lights are typically designed to provide a concentrated and directional light output, allowing them to reach the plants from as short as 2 inches to up to 2 feet or more. Their ability to mimic natural light makes them versatile for various growing conditions.

How far should a 1000-watt LED light be from seedlings?

As a general rule of thumb, the 1000-watt LED light should be positioned around 24 to 36 inches (60 to 90 cm) away from seedlings, but this distance may need to be adjusted based on the observed growth and health of the seedlings. The natural light spectrum provided by LED grow lights can help promote healthier and more productive seedlings when the distance is optimized.