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.

color spectrum

Different types of grow lights

High Intensity Discharge (HID) Grow Lights

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.

LED Grow Lights

How far should seedlings be from LED grow lights?

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.



How far should seedlings be from VS2000


How far should seedlings be from 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.

If you are still not sure how far should your grow lights be from your seedlings, you can message our Instagam or Facebook and we’ll help you out! We’re glad you’re on this journey and we want to help in any way we can.

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How and When to Transplant Cannabis Seedlings

When Should I Give up on Seed Germination

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