LED Grow Light Distance: How Far Should Grow Lights Be From Plants at Every Stage?

Growing top-shelf cannabis is a science that involves providing the right amount of light, nutrients, water, and other environmental factors to ensure success. Providing the correct distance between your grow light and the plant canopy is of massive importance for indoor growers, greatly impacting how the plants perform and helping to avoid mistakes while maintaining healthy plant growth.

This article provides a detailed yet easy-to-digest guide to hanging your LED grow lights at the optimal distance for growing cannabis. We’ll explain the ideal light spectrum for each stage of growth, necessary equipment for checking PAR levels, a grow light distance chart, and other expert tips.

Why Grow Light Distance Matters for Plant Health

Cannabis needs lots of direct light to grow from tiny seedlings or cuttings into healthy, high-yielding plants. Weed plants absorb light through pigments known as chlorophyll, which gives them their green colour. By absorbing blue and red wavelengths of light, chlorophyll also allows plants to perform photosynthesis and convert carbon dioxide into oxygen and water into glucose.

Unfortunately, incorrect light distance can interrupt or hamper photosynthesis and other important plant processes, promoting unwanted stretching, a bleached or burnt canopy, and low yields.

Key Factors Affecting LED Grow Light Distance

The ideal distance for hanging LED grow lights for cannabis depends on various factors. Below is a breakdown of how the light spectrum and intensity, stage of growth, and type of LED light influence the proper light distance for growing weed.

Light Spectrum and Intensity

LED grow lights come in different types—some emit a fixed white light (measured in Kelvins), while others offer a full spectrum with distinct spectral peaks. Here's what each type does:

3000 K (Warm White LEDs)

• Emits more red and far-red wavelengths
• Best suited for the flowering stage
• Can support vegetative growth, but not ideal for seedlings
• Common in fixed-spectrum LED panels

5000 K (Cool White LEDs)

• Emits more blue light, mimicking natural sunlight 
• Promotes compact, leafy vegetative growth
• Suitable for seedlings and early vegetative stages
• Found in T5 strip lights or early-stage veg lights

Full-Spectrum LEDs (With Targeted Wavelengths)

• Combine blue (400–500 nm), red (600–700 nm), and often far-red (700–750 nm)
• Designed to emit light within the photosynthetically active radiation (PAR) range
• Enable growers to support all growth stages with a single adjustable light
• Ideal for cannabis and other light-sensitive crops

Red Light (600–700 nm) & Far Red (700–750 nm)

• Red light boosts bud formation, resin, and cannabinoid production
• Far-red light helps regulate flowering timing, stretching, and stress response
• Typically found in custom-spectrum or high-end full-spectrum LEDs

Stage of Growing Cycle

Cannabis plants progress through three main stages before harvest: seedling, vegetation, and flower production. Below is an explanation of the different requirements regarding light intensity for each stage, measured in μmol/m²/s.

• Seedlings: 100–300 μmol/m²/s

The seedling stage is when cannabis plants are the most delicate and do not need high levels of light intensity. It lasts 2–3 weeks, and it is essential to provide a low level of intensity between 100–300 μmol/m²/s while maintaining a light cycle of 18–20 hours per day. The best way to provide your cannabis seedlings with the correct light level is to use a T5 strip light, a low-powered LED, or a dimmer (if your light has one).

• Vegging plants: 400–600 μmol/m²/s

Once a cannabis plant is around 3 weeks old and features several nodes and true leaves, it enters the vegetative stage. At this stage, light intensity can be increased to 400–600 μmol/m²/s to promote the production of leaves, branches, and stems. Indoor growers can keep their plants suspended in a vegetative state for a long time under an 18/6 or 20/4 light cycle.

• Flowering plants: 800–1000 μmol/m²/s

Changing your light schedule to 12/12 will trigger your plants to flower. At this time, you can increase the PPFD to 800–1000 μmol/m²/s. Full-spectrum grow lights use red light to encourage bud, terpene, and cannabinoid development, and also emit far-red wavelengths—essential for triggering budding and promoting vertical stretch during the flowering stage.

Type of LED Grow Light (Wattage, Design)

LED grow lights for cannabis cultivation are available in different styles, including panel, bar, and COB. Below is a brief explanation of each and how they differ.

• LED panels: These typically house diodes inside square or rectangular casings. Ranging in size and wattage, from 200 W to 800 W, panels can be considered inefficient compared to bar lights in terms of light coverage.
• LED bar lights: Bar lights use one or more LED bars mounted together on a frame. These lights typically use between 300 W and 1000 W of power, and are optimal for use in grow tents for potentially all stages of plant growth.
• COB LED: Chip-on-board (COB) refers to a method where manufacturers print integrated circuits onto a chipboard. Usually ranging in power from 50 W to 300 W, COB LEDs are compact and powerful but tend to produce more heat than bar-style lights due to their concentrated diode arrangement.

Full-Spectrum LED Grow Light Distance Chart

Below is a full-spectrum LED grow chart that highlights the correct distance to hang your grow lights during the different stages of a cannabis plant's life cycle. Keeping within the distance provided below will promote greater efficiency and avoid heat stress and stretching.

It’s better to start at the further end of the distance range to ensure your plants are responding well. If so, you can consider lowering them a bit. Another important note—check your light manufacturer’s specific PPFD map to make sure you’re using the correct distances. Every grow light is different.

LED Grow Light Distance by Plant Growth Stage

Below is a breakdown of how many centimetres above the plant canopy you should hang your LED lights during a plant's different stages of growth. Getting these distances right will help you achieve maximum yields and overall crop quality.

Seedlings

Cannabis seedlings need care and attention in order to develop a strong root system, stem, and foliage. Therefore, it is essential to position your lights at an appropriate distance to prevent seedlings from becoming stressed or leggy (etiolation) and potentially burning.

The ideal LED light distance for seedlings is 25–30 cm above the canopy. We recommend feeling the temperature of your grow light using the back of your hand to get a sense of the heat level (more on this later).

Vegetative Stage

The vegetative stage occurs once seedlings develop several fan leaves and nodes. It’s during this stage that plants develop robust branches and lots of foliage, setting the stage for ample bud development later on. As such, during vegetation, growers should increase the light intensity while also increasing the light distance to 45–60 cm as plants continue to grow taller.

Flowering Stage

Once you decide to induce flowering, the plants will experience a change in growth hormones, causing them to stretch dramatically—sometimes doubling or tripling in height—before transitioning into full reproductive growth focused on bud production.

During this all-important stage, it is best to keep the grow light 30–45 cm from the top of the canopy. This will help to prevent light-related burning or bleaching, and will help drive bud and trichome growth.

How to Measure and Adjust Grow Light Distance

How you set up and hang your LED grow light will determine how high you must raise it as plants grow. The easiest way to determine the optimal distance is to use a measuring tape and, each day, check the distance between the topmost part of the plants and the LED light.

Here are some key tips to ensure success.

Using a PAR or PPFD Meter

PAR, or photosynthetically active radiation, measures how many light photons a source produces for photosynthesis. Knowing the PAR levels of your indoor grow area will allow you to check that you have the ideal range for each stage of growth while helping to achieve peak photosynthesis and plant development rates. PAR meters are designed to measure sunlight or artificial light, and will give you a precise reading in μmol/m²/s.

• 100–300 μmol/m²/s for seedlings
• 400–600 μmol/m²/s for vegetation
• 800–1000 μmol/m²/s for flowering

Hand Test Method for Light Heat

If you cannot buy a PAR meter, you can use the hand test method as a backup. Of course, it will not be as efficient and reliable as a PAR meter. However, it will allow you to detect how much heat and light output there is in a set space. Move your hand across the centre and edges of your grow space to gauge how evenly the light is distributed, how bright it is, and whether it feels too hot or comfortably cool.

Common Mistakes When Setting Grow Light Distance

Setting up your lights is a simple task. However, there are some variables to consider to help you avoid mistakes and maintain optimal plant growth, health, and yield.

Placing the Lights Too Close

If you place your LED grow lights too close to the top of the canopy at any stage, you will inhibit plant growth by inflicting potential heat stress, negatively affecting transpiration and vapour pressure deficit, and exceeding the recommended levels of light intensity the plants require.

Placing the Lights Too Far Away

When your LED grow lights are too far away during the seedling or vegetative stages, the plants will stretch as much as possible to get closer to the source. The result is tall, lanky, and thin stems, which will prevent the lower parts of the canopy from receiving enough light to develop well.

During flowering, keeping the lights too far away will dramatically affect the size and density of buds, as well as trichome, resin, and cannabinoid production.

Not Adjusting the Distance Over Time

As your plants grow taller, it's crucial to check and adjust the light height regularly—ideally every few days—to maintain optimal PPFD levels. Failing to do so can lead to issues like light burn, heat stress, and poor bud development due to uneven canopy exposure.

Ignoring the Manufacturer's PPFD Map

LED lighting manufacturers create PPFD maps specific to their products. Ignoring this map is not advised—use it as a guide.

Set Your Grow Lights Right for Maximum Yield

LED grow lights are energy efficient and provide cannabis plants with a full light spectrum and optimal PAR levels. Awareness of what cannabis plants require during the seedling, vegetative, and flowering stages will help you become a better indoor grower.

Keeping your LED lights at the proper distance using a measuring tape, adjusting the height accordingly, and owning a PAR meter will help you get the most out of your cannabis plants during the seedling, vegetative, and flowering stages. To achieve the very best results possible, explore our range of full-spectrum LED grow lights!