How Far Away Should My Grow Lights Be?

A question we hear often is, “How far away should lights be or how high should I hang my lights above my plants?” It is a tricky question that can lead to hours of research and perhaps more uncertainty than when you started, but we are here to help! From our experience in the lighting industry, we have a few different questions we’ll need to consider along our path to figure out the best answer. Strap in, because this will be a long article!

How Far Away Should Lights Be? Why does Light Height Matter?

Simply put, the more light a plant can have the better! More light means better yield but having your lights too close to your plants will cause a number of issues—a burn on the leaves that could appear like a nutrient deficiency, or if your lights are too far away you’ll encourage stretching of the stems, which uses up valuable resources that could go towards flowering.

Different Kinds of Lights – How far away should grow lights be?

There are three kinds of grow lights commonly used by growers today: LED, HPS/MH/CMH, and Fluorescent. Each lamp has a different combination of heat output, light spectrum, and power usage. Heat output and spectrum are both keys for deciding where to put your lamp.

What is PAR/PPFD, and Coverage?

We use PAR and PPDF to describe the part of the light spectrum that is usable by plants and is able to be converted into energy by photosynthesis. PPDF stands for Photosynthetic Photon Flux Density, which measures the amount of Photosynthetically Active Radiation (PAR) put out by a power source, be that your grow light or the sun. The closer your light is, the higher the PAR intensity will be, while the coverage will be much smaller.

In the perfect world, you would be able to coat each leaf with 100% of the light emitted from your lamp, but that of course just isn’t possible. PAR and PPDF are usually mapped on a chart such as this one, which displays the PAR values at different heights:

Here we can see how height affects the amount of “light” that reaches the plant below.

LED LIGHTS – How far away should grow lights be

LED grow lights are an excellent option, they are extremely dependable, long-lasting, and are a lot less of a burden on your electricity bill. Great choice! Yet, distance is probably the trickiest thing with LED lamps, as there is no right or standard distance from the plants, and the best distance varies by both lamp and wattage.

With our LEDs, we recommend that you keep your lamp at least 12 inches above the canopy. Here is a handy chart:

We recommend that you keep a minimum 12 inches distance between your plant and your canopy. Other growers may tell you they have had different results placing the lamp close to the canopy, but we cannot speak for them and everyone will eventually develop their own style of growing, so as a baseline, we strongly recommend not putting the LED closer than 1 foot.

This is because, while LEDs do not give off the heat of HPS or CMH bulbs, they still are able to cause “Sunburn” on your plant, which will over time reduce productivity and potentially kill your baby!

High-Pressure Sodium – How far away should grow lights be

HPS is another popular lighting system that we have received many questions about. Most new growers can tell that HPS systems should not be placed too close to a plant because of the amount of heat that emits from the bulb, however, there is a lot of debate about how high you should hang your bulb above your canopy. As with LEDs, one grower may have very different results from your own, so experiment and see what works well for you!

In general, our commercial grower partners often start by hanging their HPS lamps about 20—26 inches above the canopy and as they watch their plants they can see whether to adjust the lamp height or not. A telltale sign of needing to lower the lamp includes stems stretching and too few new buds and leaves being produced.

Another classic trick to judging whether the lamp is too close to the canopy is to sit your hand directly on the canopy and wait for 30 seconds. If your hand gets too hot so as to be painful, your lamp is too close.

We sell HPS bulbs as 1000W, 600W, and 400W.

Ceramic Metal Halide – How far away should grow lights be

CMH bulbs are another popular choice of grow light and have been on the market for many years. CMH bulbs, however, run much hotter and are more prone to burning plants. We recommend that you place these bulbs around 24 inches above your canopy. This will reduce leaf stress.

Fluorescent Bulbs – How far away should grow lights be

Fluorescent grow lights are comparatively weak in terms of PAR and heat output. Our T5 bulbs are mainly designed for low-light plants that grow under heavy forest canopies and normally are not used for most indoor plants, but with the right planning and knowledge, fluorescent bulbs can produce excellent results.

That said, keep fluorescent bulbs as close to your plants as you can (without burning them)! Your plants can handle it and your bulbs will probably never get hot enough to cause any worry! Big harvests can happen with fluorescent bulbs!

Reach out to a community! There are dozens of online and local communities revolving around your plants and will most definitely be able to help you decide the particulars of your grow. You will see that there are a lot of different ways to be a successful grower and with all of the equipment you can find on the market, growing large yields has become easier than ever.

Hanging your lights is just the first step in great grow, you’ll also want to research into training your plants, keeping the right nutritional balance, and developing automated environmental systems.

If you have any questions, please don’t hesitate to reach out to us!

And be sure to check out our other blog posts for useful tips on becoming a great grower!

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