How Far should Seedlings be from Grow Light?

Let’s get detailed about lights: grow lights are the most prominent part of your tent but can be damaging to plants if used incorrectly. A grow light, especially the height from a grow light to the seedlings, is an important factor that determines if your plants can survive or not, and the amount of your yield. A systematic understanding of your lights will help your plants thrive, so let’s start with some background about lights and then talk about light height.

So how far should seedlings be from grow light? Let’s explore now!

How does a grow light work?

The reason why a grow light can be substituted as natural light is that it can provide the color spectrum and temperature plants need to perform photosynthesis. The visible spectrum (380～780nm) refers to the spectrum that people can “see”. Through prism dispersion, it can be divided into red, orange, yellow, green, blue, indigo, and purple and these color variations have different effects on the plants.

Studies show plants are most sensitive to red light, which is crucial to the growth of your plants (from sprout to flower to fruit). However, that doesn’t mean that plants should be cultivated under such monochromatic light: blue light is very important for plant differentiation and stomatal regulation as well. Plants should receive a variety of balanced light sources for their morphological development and leaf color.

Key benefits of putting your seedlings under grow lights

Controlled Light Exposure：Grow lights allow you to precisely control the duration and intensity of light exposure for your seedlings. This is crucial, as cannabis plants require a specific photoperiod to transition from the vegetative to flowering stage.

Consistent Growth：Grow lights ensure your seedlings receive a consistent, reliable source of illumination. This promotes steady, uniform growth compared to relying on natural sunlight, which can be variable and inconsistent.

Faster Maturation：The intense, full-spectrum light from grow lamps accelerates the seedlings’ growth rate and development. This allows the plants to mature more quickly into healthy, robust young plants.

Increased Yield Potential：By giving seedlings the optimal growing conditions from the start, you’re setting them up for maximum yield potential when they reach the flowering stage. Strong, vibrant seedlings translate to bigger, more productive plants.

Disease Prevention：Grow lights help prevent issues like stretching, nutrient deficiencies and mold that can occur with insufficient light. This creates an environment less prone to problems that could stunt plant growth.

How to use artificial grow lights for cannabis seedlings?

Light Intensity：Aim to provide your seedlings with a light intensity between 400-600 μmol/m²/s (micromoles per square meter per second). This intense yet balanced light level will promote optimal growth. 

Light Spectrum：Look for grow lights that emit a full-spectrum of light wavelengths, including both blue and red frequencies. This mimics the natural sunlight that cannabis plants evolved to thrive under. 

Light Duration：Cannabis seedlings do best with 18-24 hours of continuous light exposure per day. Avoid dropping below 18 hours, as this can cause the plants to become stretched and lanky. 

Light Height：Position the grow lights 12-24 inches above the top of the seedling canopy. Adjust the height as the plants grow taller to maintain the optimal light intensity. 

Continuous Monitoring：Inspect the seedlings daily for any potential issues like pests, disease, or environmental stress. Act quickly to address any problems.

Different types of grow lights for Seedlings

High Intensity Discharge (HID) Grow Lights for seedlings

HID grow lights are usually called gas-discharge lights since they work through gases. A pressurized tube is filled with certain gases and metal salts and once an electrical current passes through the tube the electricity interacts with the gas and salts, producing light. Due to the high density of the light, HID grow lights produce more heat that also stimulates growth, but you need to keep in mind not to put the lamps too close to your plants as they can get very hot and burn your plants.

HID grow lights come in three different wattages: 400w, 600w, and 1000w, so you can choose the right types based on your needs, but this wattage output also affects heat output. When hanging HID grow lights, keep them at least 12” to 15” away from your seedlings. The higher the wattage, the higher you should keep them away from the seedlings.

Fluorescent Grow Lights

Similar to HID bulbs, fluorescent bulbs use a pressurized gas and an electrical current to create light. In fluorescent tubes, there is a coating of phosphorous that causes what would be UV light to glow. Usually, we have two types of fluorescent grow lights: T12 lights and T5 lights. The output of T5 is higher than T12, so T5s are more common for growing indoors.

One advantage of fluorescent grow lights is that they rarely cause light burn since the light intensity is much softer than HID grow lights and they do not produce much radiant heat. Therefore, you can hang T5s 6” to 12” away from your seedlings. It can be a little higher from the plants when they come to the veg and flowering stage, around 12”-16”, however, T5 lights are not nearly efficient enough to grow. cannabis.

LED Grow Lights

While HID lamps can produce far too much heat and fluorescent lights do not produce nearly enough heat or light, LED grow lights make a good balance between both.

LED grow lights are made of semiconductor materials that can convert electricity into light. We’ve explained before, but in case this is your first time, by charging half of a semiconductor with a negative charge and half with a positive charge, we can send a current of electrons from one side of the grid (positive) to the other (negative). This interchange helps us create excess energy that is released as light and a bit of heat.

Compared with HID and fluorescent bulbs, the dominant advantage of LED grow lights is that they can be used in almost every situation—if you have a low-light plant, you can dim the LED; if you have a light-demanding plant you can increase the intensity without creating much excess heat. Further, LEDs have a longer service lifetime (up to 50,000 hours!), they create more light with less power, and they are a lot cheaper to operate over extended periods. It is for these reasons that more growers are switching to LEDs.

Light Schedule for Seedlings

LEDs differ from HID and fluorescent lights in that the height can vary.

We’ve put together a couple of graphics for our LEDs so you can get an idea of how high to hang your lights. Here are the recommended hanging heights from germination to seedling to veg to flower stage for the VIVOSUN VS1000, VIVOSUN VS2000, and VIVOSUN VS4000.

VIVOSUN VS1000

VIVOSUN VS2000

VIVOSUN VS4000

Of course, these heights are just reference points and you should experiment at home to see which height has the best results for your plants. Be sure to keep a close eye on your plants if it is your first time growing with LEDs as the experience is different!

Try out our recommended heights and look for signs of negative impact: if leaves turn white, brown, or yellow, and they start to curl, the light is too close and they are too hot so try hanging them a bit higher—they’ll recover quickly. If your plants are doing well, try putting the lights a bit closer to see if you can increase growing speed. Just watch for the signs and adjust accordingly.

Best Grow Lights for Seedlings

Bring Your Garden to Life with VIVOSUN’s Cutting-Edge LED Grow Lights. Experience effortless indoor gardening with VIVOSUN’s innovative LED grow light collection. Our six full-spectrum models allow you to precisely tune light to match your plants’ growth stage – from vibrant seedlings to abundant blooms.

See your plants thrive under optimal wavelengths designed by our cultivation experts. Our advanced LED technology saves energy while producing up to 20% higher yields. Take the guesswork out of growing and create a flourishing indoor oasis with VIVOSUN’s LED grow lights. Right now, shop our selection and unlock a 10% discount plus free shipping !

VS1000 Full Spectrum LED Grow Light Board 100W

VS LED Light Board is designed for professionals and hobbyists alike, providing full-spectrum lighting ranging from white, warm-white, red, and far-red light for the needs of different growth stages for your lovely plants. Five levels of adjustable light intensity can be adapted to different planting needs and apply to more planting scenarios. Just click here to GET your Best Grow Light ! 

• The Latest LED Plant Light Technology: Using Samsung LM301 Diodes, super durable
• Lower Cost & Higher Efficiency: High-energy efficiency for 2.75 umol/J only consumes 100W of electricity. More efficient than traditional HID lamps.
• Dimmable Ballast: Allows adapting to the growing needs of the plants in different periods.
• Sunlike Full-Spectrum Lighting: The VS1000 full-spectrum LED delivers optimal light-spectrum coverage—more power for your blooms and maximum PAR output at various distances, with super-bright lights that your plants will love
• Low Noise: No grow light fan is needed for the VS1000 because of the unique design of the appearance from the power supply and ventilation holes. No fan means much lower noise.

VS2000 Full Spectrum LED Grow Light Board 200W

The VIVOSUN VS2000 LED grow light delivers optimized illumination for indoor plants at every stage of growth. This innovative full-spectrum fixture produces wavelengths ranging from bright white to deep red/far-red, providing flexible light customization for seedlings, vegetative growth, or fruiting/flowering. Just click here to GET your Best Grow Light ! 

Engineered with cutting-edge Samsung LM301 diodes, the VS2000 achieves a remarkable photon efficiency of 2.9 μmol/J. The 200W power draw yields high light intensity while maintaining energy efficiency exceeding traditional HID grow lamps.

Convenient dimming from 40% to 100% makes it easy to adjust light levels for different plant needs. The VS2000’s sleek, fanless design operates silently while emitting minimal heat. Optimized for close-proximity mounting, this LED light board promotes robust photosynthesis and natural sun-like spectrum.

Ideal for both hobby and professional growing, VIVOSUN’s VS2000 LED integrates next-level technology into an accessible, versatile fixture. Experience optimized yields and healthy plant development with full control over your indoor garden’s lighting.