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Ok, so it might not be everything YOU want to know about grow lights, but it’s definitely everything I wanted to know before, er, I knew it.
Grow lights can be a very confusing topic. There’s a lot of information about wattage and colour spectrum etc etc etc when all I wanted to know was which grow lights actually worked, how long I needed to leave them on for, and how much they’d initially cost and cost to run.
Hopefully I cover everything here, but feel free to leave me a comment asking any questions and I’ll do my best to find the answer.
Anyway, let’s crack on.
Should I use a grow light for my indoor plants?
I would get grow lights if:
- If you live somewhere that has ok light all year round, then you may not need grow lights. But if you live in colder parts of the Northern hemisphere, they may help a lot.
- Do you have a lot of plants? If so, and you find that they suffer from lack of light in the winter, it might actually be more cost-effective to buy grow lights than it is to replace your plants.
- This is even more the case if you have rare/expensive plants. Or if you get anxiety when your plants die, or you have plants that have sentimental value.
- You have a dark area in your home that you want to put a plant in. Grow lights can make this happen. Just check there’s an outlet nearby first. My house has (literally) 30 outlets downstairs and two (2) upstairs.
- You love propagating/ want to get better at it. Whilst natural light is always best (it’s free for a start) it isn’t a guarantee (cries in UK). Light is instrumental to root growth and having a back up is useful if the sun has fucked off.
I wouldn’t get grow lights if:
- You can’t afford it. They’re awesome to have, but not necessary. I’ve made it through a winter without grow lights and I didn’t lose any plants. You can always trim back stunted growth in the summer.
- You don’t have many plants. Effective grow lights (especially aesthetically pleasing ones) can be pricy, and if they’re more expensive than replacing your plant, you might want to consider whether or not they’re worth it
Can any light be a grow light?
I have a whole article here on whether plants will grow under normal LED lights, and answer is yes, but not as well as they would under actual grow lights.
Lights that are designed for the purpose of allowing humans to see in the dark don’t have the same spectrum as lights designed to help plants grow.
For reference, my Mars Hydro grow light has a brightness of about 22,000 lumens. A light bulb has about 400.
Are grow lights effective?
Yes. Even the cheap grow lights I’ve found on Amazon (here’s a review)do a stellar job at not letting my plants die over window, even though they’re in the dark recessed corner of an east-facing window.
You don’t need to spend a lot of money on grow lights if all you want in terms of results is for your plants not to die.
If you choose your plants carefully (for example plants like calathea and peace lilies) you can even encourage growth all year round, though it’ll probably be a little small and stunted.
But for those of you with loftier goals, such as preventing Alocasia going into dormancy, or even encouraging healthy growth in winter, you can get grow lights that will 100% deliver that.
I know, because I have some. My boyfriend gave me some of his old aquarium lights and I am SUPER impressed with the results I’ve gotten from them (yes, there will be a mini review further on).
I recently came into possession of a Mars Hydro TS 1000w.
I don’t mean to over sell it but JESUS CHRIST my plants love it.
My other lights work SO well at coaxing out new growth but the new guy? My plants are growing like CRAZY.
It’s a semi-professional grow light, so it’s pricier than a cheap grow light but not that expensive compared to what the actual professionals use – under $200, and often on sale.
I love it SO MUCH. The only issue I have is that it’s a pain to set up. Most professional grow lights are designed to be suspended from a hook, so I had a to McGyver that in a way that wouldn’t frighten my landlord.
I came up with this, using an old Ikea shelving unit I had:
The grow light is just clipped onto the metalwork at the top:
I also recently got a Bestva grow light, which is considerably cheaper than the Mars Hydro.
I prefer the Mars Hydro, but for reasons that don’t really affect the performance, so if budget is an issue, check out the Bestva. The suspendery things are too long, and it doesn’t have a reflector (which means you can fit more lights under it, but the light is slightly less intense) but it’s a solid piece of kit.
This one I have suspended in a cheap indoor greenhouse, and it works really well. Due to the length of the wires it hangs from I can only use two of the four shelves, but that’s fine. I will say that it looks pretty sexy – definitely prettier than the Mars Hydro.
Grow lights contain UV, which can be damaging to your eyes, so don’t go staring directly at your grow lights, or sitting under them without sunscreen.
UV is added to grow lights (I’m sure added isn’t the right word, but you know what I mean) and that can cause sun stress – if your plants are turning red, that can be a sign of sun stress. The reason UV is useful is that it leads to secondary metabolites. Farmers can use UV light to increase certain nutrients or compounds like THC. Pretty cool!
Are grow lights expensive to run?
I can’t give you ‘X grow light will cost X dollars per month to run’ because there are too many variables.
But I can tell you that over the course of the past 15 years, we’ve had everything from 0 grow lights running to upwards of 10 running (as well as aquarium heaters, filters, protein skimmers, and various other fish paraphernalia) and whilst we’ve seen fluctuations in our electricity bill, never anything particularly extortionate or out of the ordinary.
Grow lights typically use LED bulbs, are are pretty efficient to run.
I’ve had the Mars Hydro running for about a month (see below how long I run them for) and it’s made very little difference to our electricity bill.
How long should you leave grow lights on for?
Ideally, they should be running for 15 hours a day. That’s what professional growers recommend.
I don’t do that.
I don’t like leaving my grow lights on whilst I’m at worry, because I’m an overthinker. What if they fall and start a fire? No thanks.
(Am I being ridiculous? Probably).
Three days a week I run the lights for about 12 hours. The other four days I run them for a couple of hours in the morning, and about four hours at night.
Bear in mind that there definitely is a maximum amount of light for plants. The 15 hour ideal is based off the natural light cycle in the rainforests that most tropical plants hail from.
You can’t hack the system by leaving grow lights on for 24 hours a day, because plants need a rest. Too much light can mess up their respiratory systems.
How close to grow lights do plants need to be?
I can’t find a definitive answer on this, but too close and your plants will burn (no closer than three inches, but different plants burn at different rates) and too far away and they won’t get much benefit.
Grow light-wise the plants that are directly below the lights are about 10-ish inches away BUT I group a few plants around them which are further away.
One thing that is, unfortunately, not possible is putting a grow bulb in your overhead light fixture and expecting that to provide enough light to stimulate growth in your plants. I’m afraid that’s too far away.
The Pilea was doing really badly before I moved her to her current position.
As you can see (she’s the one with the pancake-shaped leaves to the right of the orchid, she’s not too close to the grow light but she is growing WAY faster than she was when she was sat in a west-facing window (which was the only place she’d grow at all, but you can see that she has red leaves from sun stress).
People are very quick to say that a plant needs to be in a certain window or facing a certain way, but light varies a LOT. My south-facing window will get far less light than the north-facing window of someone living in Australia.
Also, the sun burns and dries plants out. The grow lights are warm, so I definitely have to water more often (plus they’re growing more) but i don’t have to worry about them burning my plants unless they’re actually touching them.
Can grow lights burn plants?
Yes, but they have to be pretty close. My Monstera peru loves to get all up in my grow lights business so consequently almost always has at least one burn. The enormous peace lily that I have growing in the aquarium does get burned leaves, but there’s a not a lot I can do about it because it grew so big so quickly it grew kind of around the aquarium light.
It’s since been raised up and seems happier.
In my experience, plants burned by grow lights don’t seem as badly affected by it as plants that are burned by the sun. Sure, the leaf has a black mark on it (and nothing’s gonna change that), but the rest of the plant is unaffected.
LED grow lights don’t throw out a lot of heat, and any they do have is pretty directional, so you plant would have to be pretty close to cause a burn.
The sun, on the other hand, is pretty hot (you can count on me to provide all the facts) and can burn the leaves, suck all the water out of the soil, and even heat the soil to the point where it damages the roots.
So if you leave a plant out in the garden it could die in an afternoon, but a grow light will likely only do cosmetic damage UNLESS you have a mega powerful one.
I can only vouch for the grow lights I’ve used, so if any ones used one that’s burned their plants to dust, name and shame in the comments, please.
Are purple grow lights better than white ones?
This is where it all gets a bit technical for me, so I shall provide a link here to an article that explains all about purple grow lights.
In short, it seems that manufacturers claimed that plants could only photosynthesise red and blue light, so a full white spectrum was a waste of light. Turns out that red and blue diodes are cheaper, and plants love a full spectrum.
Do purple lights work? Yeah – plants use blue and red light the most. But if you don’t like purple light, a full-spectrum white light is just as good.
It’s also worth mentioning that purple lights can give you a headache.
Which grow lights should I get?
My favourite grow light
The Mars Hydro TS 1000w is my favourite grow light. It’s so so good. My hoya freaking LOVE it, and my Pothos don’t know that it’s winter.
They’re not on in the photo on the left because my boyfriend puts everything on timers – mostly for the terrarium you can just see on the shelf below.
Pros of the Mars Hydro 1000
- Cheap to run – there was no difference in our electricity bill.
- It’s bright but face down so they’re not blinding. Don’t look directly at them
- They work. Pretty much all I’m looking for in a grow light.
- They produce a bit of warmth, which not only helps my plants, but it can help raise humidity
- The light is white without being stark – it mimics natural light super well in terms of colour.
Cons of the Fluval COB
- They’re a pain in the arse to hang. I’d love if they came with a way to attach them to shelves.
- They’re pricier than I would buy if I were a beginner. This is a shame because in my opinion, they’re extremely good for demonstrating just how important good light is. Also a great way to rehab dying plants.
Full disclosure: I got sent this light for free. I honestly don’t know if I’d have bought a grow light like this (because I like to keep my plants on shelves) but I am definitely a convert. It’s incredible.
My budget grow light pick
There are loads of these cheaper options, and they do a decent job. Don’t expect a tonne of growth, but they will give your plant enough light to stay alive.
Pros of the relassy grow light
- Easy to clip on to shelving
- Cheap and cheerful
- They come with replaceable bulbs. The ‘how long do the bulbs last’ question is answered in the cons part
- They do the job. Nothing startling, but my plants are alive
- The goose neck designs means you can direct the light wherever you want. Extremely useful if you’re a winter jigsaw puzzler like me (or knitter or reader). I’d repurchase for this feature alone.
Cons of the Relassy grow light
- Leaving the lights on for more than five hours can affect the longevity of the bulb. I leave mine on for longer, and so far the bulbs have lasted. I’ll update when I need to replace but so far (over a year) they’re fine
- They come with a plug but the actual unit has a USB adaptor. And every time you slightly knock it the lights flicker – but only the tiniest amount so at first you don’t know what’s going on. Ghosts? Murderer? Who knows?. It’s a minor inconvenience but it can be annoying.
- The light is quite warm. It doesn’t bother me, but I know some people don’t like it.
A medium-priced grow light
I also got sent this Bestva grow light, which is also a 1000w one, like the Mars Hydro.
Pros of the Bestva grow light:
- It’s pretty cheap – about half the price of the Mars Hydro
- It looks really good. Definitely the most aesthetically pleasing of the bunch
- It works really well – not as bright as the Mars Hydro, but waaaay better than the Relassy.
- It’s cheap to run – again, no impact on our energy bills
Cons of the Bestva light:
- Hanging it is a pain, and the wires it hangs from are really long. Great if you can suspend it from the ceiling, but not otherwise
- No reflectors, so the light disperses more. Tbh this is fine by me – sure, the plants get a little less light, but you can surround the light with plants and it’ll reach farther.
Regular lamps as grow lights
I have a lot of dark corners in my house, and a lot of plants. This lamp with a regular bulb (sorry, I’ve no clue what the wattage is, but it’s probably from Ikea) does a decent job of keeping my Philodendron Imperial red and Thaumatophyllum selloum alive. They don’t put out much growth, but they’re, you know, not dead.
Incidentally, that philodendron is in Leca, and converted like a freaking DREAM. It really makes watering easier in winter, The selloum had to live outside in the summer (thrips love him) but he’s been allowed back in for winter.
A wild card pick for best grow light
I recently got myself an Aerogarden (and my herbs are GROWING!) and it’s been a welcome source of additional light. My smaller succulent and African violet are enjoying the extra light, and whilst it was pricy, it’s a great multi-tasker if you’re looking to grow your own food or just give hydroponics a try.
Final thoughts on grow lights for house plants
Are grow lights necessary to keep house plants alive? No. Unless you live in a cave, your plants will probably survive the winter. However, if you have a lot of plants and the thought of them struggling is anxiety-inducing, then a grow light is great for peace of mind.
You don’t need to shell out on fancy ones if you can’t afford it (or don’t want to). I probably wouldn’t have had my boyfriend not had spare ones (#perpetuallycheap), but I’m glad I had the opportunity to try them, because they’re awesome.