How close should grow lights be to indoor plants?

I wish I could just tell you one exact measurement, but not only do different indoor plants have different needs for light (no shocking news there), but their needs also change depending on what growth stage they're in. Plus the intensity of the grow light also changes how close or far away they should be positioned.

So coming up below I've included the distances and considerations for germinating seeds, for seedlings, unrooted vs rooted cuttings, foliage and flowering; as well as what area size different lights cover, and the best-match options for different situations in commonly available lights. 

Let's jump in and shed some light on the question (sorry, I couldn't resist the pun), of the right distance to position grow lights from your indoor plants...

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The General Rule when lighting indoor plants

As a general rule-of-thumb for LED grow lights, indoor plants being grown for their foliage need 10 to 40 watts of light per square foot. The lower end for low to medium-light indoor plants, and the higher end for bright indirect to direct-sun lovers. Unless your plants needs direct sun or very bright indirect light, stick to 20 to 30 watts maximum. 

One square foot is 30cms x 30 cms (about 12 x 12 inches). A standard plant shelf or small coffee table is around two square foot, about 60cms long by 30cms deep or 24 x 12 inches. Lights like these clip-on PHOTO+ Double Grow Tubes are 20 watts and the PHOTO+ Triple are 30 watts.

One reason it's only a general rule however, is because wattage and brightness aren't everything that matters. A lower wattage light might be less bright to our eyes, but produce better quality of light for our plants. For example, those pinky-purple grow lights that are a combo of blue and red grow lights, appear quite dim to our eyes. 

Definitely take the time to read up about the light you're looking at buying. Most suppliers provide a LOT of information to help you work out if it's the right light for your needs (or for those in New Zealand you're welcome to ask me, I'm happy to help you choose the right light).

A warning before you buy grow lights

Before you buy grow lights for your indoor plants based on the 10 to 40 watts 'golden rule' keep in mind most indoor plants get some light from natural sources also. It's rare your grow light will be your only source of light in an otherwise dark room. That means your grow light does NOT have to meet your plant's needs all by itself (and if it did, you might be going overboard which can result in bleached and scorched leaves, ouch). 

One lower wattage grow light may be plenty for covering multiple indoor plants, or a small to medium plant shelf, when there's good natural light for at least some of the day. Like the PHOTO+ double (20 watts) or triple (30 watts) for example, or one or two 15 watt Sansi grow bulbs (Sansi are also available here on Amazon for those not in New Zealand). 

Watch out for 'tomatoes'

Also keep in mind a lot of indoor plant grow light advice online is based on growing, um, tomatoes (if you know what I mean). 'Tomatoes' do not have the same bright indirect light requirements that the majority of our Amazon rainforest floor and rainforest canopy plants do. 'Tomatoes' need more like 30 to 50 watts per square foot when using LED grow lights and to flower, it's more like 40 to 60 watts per square foot. 

If your source doesn't outright say it's for 'tomatoes' then look for what the website sells (if it's a hydroponics brand or store that's a common giveaway). Buying a grow light for your Monstera, Philodendrons, Pothos and similar, based on advice for 'tomatoes', could mean you end up burning and bleaching your plants. 

How close should grow lights be for propagating cuttings and for germinating seeds?

For germinating most seeds and for unrooted cuttings, LED grow lights can be further away or dimmer, as light requirements are lower at this early stage. Start around 60cms away, or if your grow light has adjustable brightness, turn the brightness down and position them closer, around 30cms. 

What distance should grow lights be for seedlings and rooted cuttings?

Once seeds have germinated and start growing their first true leaves, or when rooted cuttings and recently potted up cuttings begin producing new foliage, move your grow lights closer or turn the brightness up, as the light requirement goes up considerably at this stage.

Depending on the heat and intensity of your chosen grow light, you could go as close as 15cms, but as a general rule start around 30cms and adjust closer (or further away), if needed.

A cool-running LED grow light is a good idea for this stage too as tender new foliage can be more heat sensitive. Keep an eye out for leggy, stretching stems or smaller leaves (a sign more light may be needed and grow lights could be turned up or moved closer). Stunted or very compact growth can be a sign the light is too intense. Also watch for fading or bleached leaf colour or scorching (a sign to turn the brightness down or shift the lights further away).

For my rooted cuttings and baby plants in my converted Ikea cabinet (I have a Rudsta Wide, below), I use the strip-type LED grow lights. They run a bit warmer too which helps me keep the temperature higher in my cabinet. For the locals the ones I use are these Grow Bars, or for those not in New Zealand, have a look at the Barrina T5's on Amazon.

For my cuttings and younger plants 'out in the open' I just clip one of the Grow Wand or PHOTO+ type lights to the bench, shelf or table that they're on. I find those run really cool also. If you go for the clip-on type, I'd suggest getting at least a double and positioning the two tubes either side for good coverage, so plants don't lean towards a single light source. The singles are great value but better only as a supplementary light source in an otherwise well lit area, since they only offer light from one direction. 

If you don't have anything to stick-on or clip-on your lights to, a Sansi 10 watt is a great option instead. They're not much bigger than a standard light bulb and fit in most standard desk lamps and floor lamps.

What distance should LED grow lights be for established indoor plants?

 
Once your plants have matured a bit, or if you've bought them from your local garden centre already well established, they still have a higher light requirement if your focus is on growing plants for their foliage, not flowers. This is where the range of 20 to 30 watts per square foot is helpful to know (lower for light sensitive, and higher for direct sun lovers), taking natural light into account also.

My largest plant shelf is so big (about 2 metres wide x 1.8 metres tall which is approx 80 inches x 70 inches), that there aren't many places it fits at home. The natural light level where I have it is low to medium light at best, making winter a struggle, which means grow lights are a must for me.

I use the Sansi grow light bulbs in floor lamps for them. The Sansi ones are very bright and intense so I position them further away. I use two Sansi 24 watt bulbs to cover my largest plant shelf, positioned about 1.5 to 2 metres away from my plants, either side of my plant shelf so plants don't lean or get leggy. You can get the Sansi 24 watt on Amazon too. Unless you've got an extra-large area to cover, two Sansi 15 watt bulbs are usually plenty for most size plant shelves and small plant rooms. 

My smaller plant shelves are 3 to 4 shelves high and measure about 1 metre tall (about 40 inches), by about 60cms wide (about 24 inches). For those I either use those stick-on strip-type grow lights (I use Grow Bars myself but if you're not in NZ a similar type are Barrina T5's available on Amazon), which I stick on above the middle and lower shelves where natural light is naturally lower. For my other small to medium plant shelves I love those tube-type clip-on lights, like the PHOTO+ triple. I just clip them on the middle shelf and position the wands so all 3 shelves get about 10 watts each of light. Perfect.

For the lower-wattage strip-lights and tube-lights I position them anywhere from 15cms to 30cms away from my established plants, although it's best to start around 30cms away and adjust from there based on how your foliage handles the light. If you're worried about your sensitive or variegated foliage, looks for lights where you can either turn the brightness down or they mention they're made for sensitive or variegated foliage (like the PHOTO+ are). 

What distance should LED grow lights be for flowering indoor plants?

 
For flowering, some plants need the light level lowered, some increased, depending on variables such as whether they are summer or winter flowering. If your plant isn't flowering, look up first if 'not enough light' is a common cause of not flowering (which is the case for a lot of our indoor plants such as Peace Lilies, Orchids, Anthurium, Hoyas and African Violets), and increase their light level. That doesn't mean you need to go out and buy a new grow light. You can also simply shift your grow light closer, have it on for more hours, or turn the brightness up. 

Keep learning about grow lights

Yes, you're right (although it's probably obvious if you've got this far), this absolutely is a simplified way of working out the general distances for different plants at different stages of growth.

And yes, there's WAY more to the complex world of grow lights. Wattage may a common way to help select grow lights, but really isn't the ideal deciding factor, especially if your plants are relying on your grow lights for their only source of light.

If you want to learn more about the different terms and find out more answers to grow light FAQs, including what lux, PAR, IP, Kelvin and more mean (and why they matter), this one's for you...

Read the ultimate guide to choosing grow lights for indoor plants >