Grow lights are an incredibly useful piece of equipment for houseplant people, but it is a very confusing topic for beginners.
Unfortunately, there’s always going to be a bit of trial and error when it comes to using grow lights on houseplants.
If you’re growing tomatoes indoors, there is a tonne of information out there that will tell you exactly what spec grow light you need, but there isn’t much research into the light requirements of houseplants (especially aroids). So… no one really knows. Different houseplant experts use grow lights differently.
This article will give you the information to help you choose the style of light you need, and how to run it, but you will need to experiment a bit.
When to use grow lights
There are loads of different ways to use grow lights. They’re not just useful for grow tents and cabinets.
To light up a dark corner
Growing houseplants in low light is a great way to get acquainted with pests and root rot. If you have a dark corner that’s screaming out for a plant, a grow light can make it a more hospitable environment.
You don’t even need a separate light – you can put grow bulbs in lamps you already have.
To provide supplemental lighting in winter
I run my grow lights for about six hours a day – two in the morning and four in the evening, and let the sun manage on its own during the middle bit. It is free, after all.
To boost growth
Adding grow lights is a great way to size up or mature houseplant leaves. Monstera and Pothos can both grow huge and fenestrated, but need a lot of light to do so. A grow light can give it that extra boost need.
To light a plant room
Got a weird box room that’s not good for much? If you invest in a decent grow light and hang it from the ceiling, you can create your own plant room.
To light a plant cabinet
Plant cabinets are a great way to grow plants that need super high humidity without needing a humidifier. Adding grow lights not only maximises growth, but it makes the cabinet into a pretty cool feature.
Be careful not to go too strong on cabinet lights – it’s a pretty small environment and you can end up stressing plants out.
How to choose a grow light
Don’t overthink it.
Unless you fork out the £100+ needed for a PAR meter, you’ll never know the exact specs of your grow light because it depends on existing light and the way you’ve set up your lights and plants.
Add that to the fact that there isn’t really enough research into houseplants to truly know their light requirements and we come to the conclusion that we’re bound by our budget and the reviews of other people.
There are the things you need to consider:
How big a space do you need to light?
If you’re lighting a whole room, invest in one big grow light. Hang it light, and experiment with moving it closer and further away.
You’re better off spending £500 on one grow light than having to buy a tonne of smaller ones.
Budget
Professional grow lights are pricey. If you can’t afford them, try searching for warehouse lights instead, and read the reviews. A lot of people use them as grow lights and they work well.
Different types of light
There are three different types of grow lights:
- Fluorescent lights
- High Intensity Discharge (HID)
- Light Emitting Diodes (LED)
Just use LEDs. There are hundreds of grow lights on the markets and narrowing your search down to LEDs will help a lot.
Professional growers use fluorescent lights and HIDs (as well as LEDs) to better control the different stages of growth of their plants.
There isn’t enough research on the use of other types of light with houseplants to make it worth researching them. LEDs offer the best value for money (both in terms of purchasing and running costs), they don’t emit too much heat, and they’re very effective.
Different styles of light
Are you looking for lights to attach to shelves?
A suspended light?
Grow bulbs to fit in existing lamps?
Be clear on how you want your lights to look before purchasing. If you want to light a whole room, using tube lights won’t be particularly efficient. A professional hanging grow light will be overkill for a peace lily in a dark corner.
Specification
The two measurements we’re interested in are PAR and PPFD.
PAR stands for photosynthetically active radiation.
PPFD stands for photosynthetically active photon flux density.
PAR (in very basic terms) measures the amount of light coming from the grow light that a plant can use for photosynthesis.
PPFD is the amount of PAR that’s hitting the leaf.
You can use PAR and PPFD to measure the daily light integer, which is the amount of light a ppant receives in a day.
We measure PAR in umols.
Lux, lumens, footcandles are all measures of light humans can see. Whilst it can be helpful (because generally brighter light has a higher PAR), plants can’t see, so it doesn’t make sense to buy a grow light using these specs. However, since cheap grow lights never have a PAR reading, (and PAR meters are expensive) sometimes we have to use lumens.
Lumens vary a LOT in grow lights, but more is better. A decent grow light emits about 28,000.
- We don’t know enough about houseplants spectra preference to know whether they prefer red or blue light, but they do best in full spectrum
- Good grow lights are between 5000-7000 kelvin
What’s the ideal grow light setup?
We want to maximise the DLI – i.e. the total volume of light a plant gets in a day.
16 hours of medium light is better than two hours of bright light.
With grow lights, we tend to focus on light intensity, and keep grow lights close to our plants.
A very powerful light further away from your plants is much more effective (though more expensive).
It makes sense – it kind of mimics the sun, which is…pretty far away.
Cheap grow lights need to be close your houseplants to have any effect. The light intensity is high, but the volume is low.
Think of two hoses blasting water at the same pressure, but instead of water, it’s light.
One of the hoses is wider, so it emits more light, despite having the same pressure as the narrower one.
Plants want the wider hose.
An ideal houseplant setup would be a powerful growlight like the Mars Hydro ts 3000 about four feet above the plants, running for about 16 hours a day.
You could run a less powerful grow light closer to the plants, but the light volume would be lower.
The advantages of having a high light volume is that the plants are more evenly lit and you can fit more lights inder one grow light.
The disadvantages are…it’s hard to make professional grow lights look aesthetically pleasing without making the room a dedicated plant room.
I don’t do this by the way. I suspend my Mars Hydro ts 1000 a few inches above my plants, but the lower light plants still benefit from being around the light, not necessailry right under it.
Which houseplants will benefit from a grow light?
Most houseplants will benefit from a grow light because plants like consistency.
However different plants will prefer different levels of light.
Plants like Monstera deliciosa and succulents like a LOT of bright light. Plants like Philodendron prefer a bit more shade, Calathea even more shade, etc, etc.
One of the benefits of using a high volume grow light is you can arrange your plants so that those that need more light are closer. They form a canopy and can provide shade for other plants.
Plant cabinets and shelving units can also be arranged so that plants can be closer/further away from them, but it can be trickier when you have to navigate shelves.
When lighting plant cabinets, don’t go too strong with the lights. A lot of people keep Philodendron in light cabinets, and too bright a light can stress them out. Light cabinets are great for keeping high humidity and consistent conditions, but the lighting situation isn’t always ideal for them, purely because they have to be so close to the lights.
Quick-fire houseplant grow lights questions:
Does the colour of houseplant grow lights matter?
No. But plants look awful under purple lights.
If you like purple get purple. Enjoy the inevitable migraine that comes with it
If you’re after a scientific answer rgarding the spectra preference of houseplants, I’m afraid no one knows.
Will houseplants grow under normal LED lights?
Probably not. Unless:
- The light is very close to the plant. Like, an inch away
- You’re running the light for 18 hours a day
- The plant prefers lower light – like a Calathea or a peace lily
They can provide enough light to keep plants alive though, and can supplements natural light in winter.
How close do grow lights need to be to houseplants?
It depends on the strength of the grow light.
Ideally, the light should be about four feet away to maximise the DLI, but you’d need a really strong grow light to provide enough PAR.
The closer the light is to the plant, the higher the PPFD, but that can lower the DLI (daily light integer) because the light is concentrated in one place.
It’s very confusing. Trust me, if there was one right answer I’d tell you, but there isn’t.
I’m pretty sure that in the photos on this article, mine are all a bit too close. My plants grew really well (though there was some bleaching) BUT if I had them a bit higher I could have fit more underneath them.
How long should you leave grow lights on for?
Your plants need about 16 hours of light per day.
As I mentioend in the beginning, you can use grow lights to supplement natural light, so use them in the early morning and evening, or leave them on for the full 16 hours.
Plants need to rest as well. Leaving them on for 24 hours will stress them out.
Benefits of grow lights
- They offer consistent levels of light
- They can also provide a bit of heat to plants, which is useful in winter
- Giving plants good light strengthens them, and makes them better at fighting off pests and disease
Disadvantages of grow lights
- They can be costly to buy and run
- There’s a certain amount of trial and error involved. Everyone’s lighting situation is different and there’s no official research into how much light houseplants need
Grow lights I recommend:
I have the Mars Hydro ts 1000, and it works really well. The ts 3000 is a more powerful version, and can be used to light a whole room. The Barrina shelf lights are an awesome options for shelving – they’re pretty cheap and work really effectively.
Grow bulbs
Grow bulbs are another option – you can screw them into existing lamps. Make sure the bulbs are no more than a foot or so away from the plant, or they won’t have the desired effect.
Sansi
I hope this was helpful. I tried to keep it as concise as possible but it’s a complicated subject not made any easier by the fact that…no one really knows what light houseplants grow best in. There is a tonne of variation.
Take comfort in the knowledge than ANY extra light will help your plant out.
Before you go, you might find these articles useful:
I just discovered your site, and it’s instantly my go-to place for houseplant talk and advice. I’m fairly local (Shetland Islands) and share the reduced daylight in winter, and so many other aspects of growing tropical-type plants indoors up north. I grow mostly foliage plants with interesting shapes and colours, from odd stem + leaf cuttings bought on eBay; turns out I have very green fingers, so there are plants by every window and skylight. Your articles are a joy…..well done.
Thanks so much! Haha, I never considered the Shetland Islands as being fairly local, but I guess relatively speaking, it really is! I LOVE buying stem cuttings, even for plants you can find easily. The golden pothos cutting I got a couple of years ago has WAY better variegation than any full plant that I’ve seen.
THANKS FOR THE ARTICLE. I WANTED TO ASK YOU HOW YOU ACCLIMATE PLANTS TO A NEW LIGHT. I HAVE NEW ONE THAT HAS UV AND IR LEDS AND I NOTICE THAT SOME PLANTS THAT I HAVE PLACED HAVE LIGHTER SPOTS ON THE LEAVES AFTER PLACING THEM UNDER THAT LIGHT. ANY ADVICE ON HOW TO ACCLIMATE THEM? THANK YOU!
Just move them further away from it and gradually move them closer over a couple of weeks. If it’s an overhead one you should be able to raise it. Some plants are more prone to bleach than others, so they may never be able to be directly under it. My P. squamiferum only produces white leaves when it’s directly under a grow light.