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LED Grow Lights Distance for Indoor Plants

phlizon led grow light

Today, more growers are changing into LED grow lights from traditional HID and fluorescent T5 grow lights. Compared with traditional grow lights, LEDs produce less heat than traditional grow lights which means that the LED grow lights are more energy-efficient. Plants need different heat and lightness at different stages and grow light distance impacts the different phases of plant growth.

How To Measure Light for Plants

First, let’s learn about PAR and PPFD. PAR (Photosynthetically Active Radiation) describes the portion of the visible spectrum that plants “see” and use for photosynthesis (400nm-700nm). PPFD (Photosynthetic Photon Flux Density) measures the amount of light (PAR) a plant receives over time. PPFD represents the light density a plant receives over time and is measured in micromoles [of photons] per square meter per second.

As we all know, plants need sunlight to produce energy, and LED grow lights pour the light into plants. PPFD is used to measure the amount of light (photons) the light source “pours” onto the plants. PPFD is an important measurement. Growers usually use PPFD MAP to measure the light intensity accurately for photosynthesis at the canopy level. Also, growers have to change the distance according to different growth stages because plants would be burned, bleached, stunted, or discolored if the LED grow lights were put at an improper instance.

LED Grow Light Distance Chart


phlizon distance chart

* The distance chart shown here is without any reflector or tents. Coverage is varies based on the distance and the LED grow light used.

Changing the distance of the same light source, the light intensity and “light footprint” or canopy coverage a plant receives also changed accordingly. As the light source is located closer to the canopy, the light intensity increases. In general, grow lights should be mounted closer to the plant canopy for vegetative stages of growth and higher up (further away from) the plant canopy during the flowering stages of growth.

How Far Should Grow Lights Be Located

In common, LED grow lights should be located between 24-36 inches above the plant canopy during the seedling stages of growth. But sometimes you should also make the difference according to the power (wattage) of the LED grow light. Generally, the light source should be located at the furthest distance during the seedling stage (~36”) – to make sure that the heat and light intensity wouldn’t be too high and prevent seedlings from burning. When roots have been established and sprouting has started, the lights can be moved closer (usually within the first 2-3 weeks).

During the vegetative stages of growth, LED grow lights should be located between 12-24 inches above the plant canopy. During this period, light sources should be located closer to the plants cause plants need more light for photosynthesis. When the plants come into the flowering stage, the plant needs the light of higher intensity to increase in height and grow fruit so the light source should be located between 18-24 inches from the plant canopy. Usually, you don’t need to change the distance during flowering. But you could make the changes according to the light you use and how you want your crop to grow.


Seedling is the very early stage of growth. During this period, plants are delicate and require less light intensity. Just hold the grow lights at somewhere between 24-36 inches from the top of the soil. Then the seedlings will grow gently.


Clones are the clippings or cuttings from a mature plant that are used to grow another plant of the same kind. Clone need more light intensity to begin so the light source would be better to be located between 14-36 inches from the top of the plant canopy depending on the wattage of the light and status of the plants,


When plants enter the flowering stage from the vegetative stage, their needs also change accordingly. During this stage, the light source should be located between 16-36 inches from the plant canopy. Moving the grow light closer will increase the light intensity which photosynthesis. However, if the grow lights are too close above plants, they can cause wider, more sprawling growth or can even damage the plant.

phlizon full-spectrum led grow light

Adverse Effects of Too Much Light

No matter what stage, when plants get too much light, they often show symptoms of distress. When using LED grow lights, the main issue that needs to be paid attention to is any indication of “light burn”. Another side-effect is discoloration also caused by closer distance, or stunted/irregular growth. These must be monitored and adjust the grow light height accordingly.

Signs of light burn in plants include upward-pointing leaves and what is known as “bleaching”. Bleaching is the white or yellow discoloration on the leaves closest to the light. Light burn can also be identified when the plant veins stain green as the rest of the leaves turn yellow.

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  • Miya Lin
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