Just like SAD lamps get rid of the blues for those with seasonal affective disorder, indoor grow lights have an even better effect on house plants.
Plants are alive and to keep them that way, they need light (not necessarily sunlight). While we need Vitamin D from natural sunlight, plants don’t.
That means you can grow any type of plant indoors with the right light systems or just bulbs, because light energizes plants through photosynthesis (it’s not as complicated as it sounds).
Only a handful of things are needed for that to happen:
The lighting systems used by indoor gardeners help to control much of those elements. In particular, the temperature and humidity (obviously the light as well).
A Deeper Dive into Encouraging Photosynthesis
For those who weren’t quite awake in biology class, the green on plant leaves contain a chemical called Chlorophyll. On each green leaf, there’s teeny little holes (Chloroplasts) that let light penetrate through them reaching into the plant stems.
(You can try this now)
Look at any plant leaf, you’ll notice there’s little veins (a venation pattern) on them. Those work just like our own veins.
Instead of transporting blood around our bodies, the veins on plant leaves transport (and store) water and sugar molecules – glucose is produced when light hits it – around the plant.
Now, about those sugary parts…
When light hits plant leaves, the chlorophyll is energized. At that point, the plant can produce glucose. Well, not quite (let’s rewind a bit). You see, water and air is needed too.
Think of it as a three-pronged feeding system for plants.
- You water the plants – the roots soak up the nutrients
- The carbon dioxide from the air is absorbed into the plant leaves (travels through the veins), reaching into the stems
- Light hits the leaves, activating the Chlorophyll
With all three combined, Glucose is produced.
For those who do remember that biology lesson, the formula looked like this:
6CO2 + +H2O + Light = C6H12O6 + 6O2 (See the simplified image here)
Don’t stress too much about this; You don’t need a biology degree to grow healthy indoor plants. It just helps to know how things work.
All you need to remember is the combination of carbon dioxide (from air), water, and light is what causes the Chlorophyll to energize, by which point it’ll produce glucose.
And that, dear indoor gardener – is photosynthesis in a nutshell!
Combine the glucose with oxygen and plants have all the nourishment they need to grow (not just survive indoors). In essence, plants feed themselves. Pretty cool!
So, with air, water and light, photosynthesis can happen. So (in theory), any plant can grow indoors.
But, there’s these other two pesky problems:
Both of those are related. The higher the temperature, the more water the plant will need. And the more water there is, the less humid it is, depending on the heat.
Remember this bit…
The type of indoor lighting system used affects temperature, in turn, affecting humidity levels.
If you’ve ever tried growing plants under artificial lights, you may have learned the hard way – plants burn.
It’s the same for outdoor plants under direct sunlight. Hold a magnifying glass over it for long enough, you’ll singe it, eventually burning a hole right through it, and could even set it ablaze.
Who remembers playing with magnifying glasses as a kid?
Here’s the thing, it’s not the light that burns indoor plants, nor is it the light intensity. It’s the heat coming from the light bulb that can wind up frying your plant.
The worst offenders are High-Intensity-Discharge lamps (HID lamps) – High-Pressure-Sodium (HPS) lights and Metal-Halide lamps. Put those too close and you’ll cook every plant under it, not to mention, run up a huge electric bill!
With that in mind, here are…
6 Types of Indoor Grow Lights
1 – High-Intensity-Discharge (HID) Lighting
These are extremely powerful lighting systems. They’re super expensive to run and can be fitted in garages or rooms with zero sunlight to grow plants requiring low to medium light intensity.
The way they work is using tubes filled with gases in the same way fluorescent tubes work (coming up).
The types of HID lights are:
High-Pressure-Sodium (HPS) Lighting
HPS bulbs are on the warmer side of the color spectrum (red and oranges) They’re best used for flowering plants.
Metal-Halide (MH) Lighting
MH bulbs are on the cooler side of the color spectrum (cool white with a blue hue). They’re best used to promote plant growth.
The intensity of the light from each type of HID light is the most intense you’ll find. Installing them is a different matter as they need ballasts.
For HPS systems, an igniter is used. MH systems don’t have an igniter, so if you decide that HPS is the way to go, you won’t be able to alternate by switching to a MH bulb.
In other words, you can either use them for flowering plants or for foliage growth. Not both. Unless you install both types of ballasts to run a combination of HPS and MH lamps. Pretty pricey!
More importantly, they produce heaps of heat. Having plants too close to the bulbs will burn them.
An even bigger problem for compact spaces (don’t overlook this), the heat may be too much for comfortable living conditions. That could drive your energy costs up further if you have to continuously run your HVAC system to get rid of all that heat.
The only real use these would have in a larger home, would be for growing lots of tropical plants.
In terms of the growing area under each bulb, you’d be looking at a 250-watt HID bulb for a growing area of just 3 x 3 feet. Using a 100-watt HID bulb could give you a growing area of 8 x 8 feet.
Keep in mind the heat from these. As your plant grows, you’ll need to adjust the height so the bulb never gets too close to the plant, causing it to burn.
The test to do is put your hand at the top of your plant. If it’s too hot for you, it is too hot for your plant as well, especially when you remember your plant is under that heat for hours every day.
2 – Fluorescent Lighting
Fluorescent lights can be decent for growing indoor plants for a few reasons…
The main one being the running costs. It’s, well, much more energy efficient than incandescent light bulbs. Not just in terms of running costs, but also for the life-span as these will last up to 10x longer.
Additionally, there’s less heat output. So not so much of a worry about the bulbs heat burning your plants.
And provided it’s not fixed in place but instead suspended from the ceiling using adjustable chains, you can adjust the height to suit the size of your plant – as it grows.
You can have these lights as close as 6-inches to the top of your plant because of the low heat.
3 – Induction Lighting
These are a step-up from fluorescent lights. They produce the same type of light but require no warm-up time. The intensity of the light is instantaneous.
The main difference here is there’s no electricals inside the tube. It’s gases that are activated by an electromagnetic field. Because of that, for home-use, they’re fairly inconvenient as they’ll drop your Wi-Fi signal and affect your cell service.
They’re also noisy. Besides, they’re not designed for home-use. They’re industrial strength, lasting thousands of hours and most suited to commercial growing operations.
4 – LED Lighting
LED (Light-Emitting-Diode) is the least expensive indoor grow light to run, but not necessarily to buy and setup, depending how many you need. Operating costs are reduced (according to most suppliers) by as much as 60%. Some claim higher.
A note on suppliers…
LED grow lights are a growing breed. As such, there’s knock-offs galore. When that happens, stick with brands. It will be more expensive, however, LED brands that’s been around for a while, have invested in research and testing. There’ll be a higher degree of trust with a brand name LED supplier with a reputation, compared to, hmm, you know, eBay.
The things that takes a couple of months to arrive from overseas? Those aren’t the kits to go with.
Onto the types of LED grow lights/bulbs…
The wavelengths required for plant growth range between 300nm (nanometers) to 700nm. The lower end of the scale is the blue and it warms up to red. Blue’s good for growth, red for flowering plants.
The sweet spot for LED lights are 630nm to 660nm (think peak time sunlight on a summer’s afternoon) and 460nm for the blue wavelength.
Another thing to pay attention to is cooling fans. LED bulbs don’t give off much heat so they can sit close to the plants, but as it’s constantly on, the counterparts of the bulb can intensify.
So, your best bet – use a kit that has cooling fans integrated. It’ll last longer.
5 – Halogen lighting
Halogen lights only emit red light, so on its own, it’s useless for plant growth. If using these, you’ll also need a source of blue light. Probably fluorescent or LED.
However, the running costs of these are close to your standard incandescent bulbs, so not the most efficient. In fact, not at all compared to the other types of grow lights.
When you factor in you’ll be running these for at least 12-hours daily, it’s just too expensive.
6 – Incandescent Lights
Just your typical house bulb can be used as a grow light but it’s going to be producing a lot of heat and like the halogen, it’s high on the red light, low on blue, and far from cost efficient for indoor growing.
They’ll rocket your electric bill running them constantly every day of the week. Besides, they give off heaps of heat making them inefficient at controlling the temperature plants are kept at.
With the light directed on them, so too is the heat they get. It’s no longer room temperature and it can cause leaf burn.
Which lighting is best and why?
Fluorescent lighting is the most cost-effective method to get up and running growing indoor plants.
With that being said, you’ll get far better growth and flowering using LED or HID type grow lights. Those are the most popular and for good reason.
Here’s a comparison video explaining the two (it’s biased toward LED, but it does explain the differences well):
You’ll notice a lot about indoor grow lighting is centered on full spectrum. All that means is there’s a balance of blue wavelengths and red wavelengths. Sometimes, UV light as well. That can be beneficial but not as much as blue and red light.
- Red wavelengths are ideal for flowering plants
- Blue wavelengths are best for foliage growth
Full spectrum bulbs hit a sweet spot that mimics sunlight, but only for peak times like sunlight at noon when it’s at its highest. To control lighting indoors, timers can be used and with one, you can really imitate natural seasonal lighting.
In summer months, there’s more light. In winter months, there’s less. Using a timer on your indoor grow lights will let you automate the number of light hours your plants get.
Take for example, growing succulents indoors. Those are dormant in the winter months. So, to grow those indoors, you’d need to allow for a dormant period. In other words, pretend it’s winter.
Do that by controlling the light hours. 20 hours per day for summer growing, and when you want to let the plant go into its dormant phase, gradually lower the light hours until it’s down to 16 hours per day of light, then gradually ramp it back up.
Now, by far, the most pressing questions about indoor lights for plants are…
How Far and For How Long?
These are tricky to answer and all too common. The reason?
Put the light source too close and you’ll burn the plant. Then again, put it too far away and you’ll find your plant uses up the energy to grow upwards toward the light… instead of flowering.
You’ll wind up with leggy plants, frail and not very healthy looking at all!
So, for distance the tricky part is the heat. Not so much the light. Do a hand test and if you feel it’s too hot hitting your hand, it’s too hot for your plant.
But, that depends on the plant. Some thrive in high temperatures, while others collapse. Also note that the more heat the plants are getting from a light source, the more they’ll need watering as the heat will cause the moisture to evaporate.
The distance to have your lights away (or close) to plants depends on the type of light you’re using.
- Incandescent and halogen light bulbs – 24 inches above the plant
- Fluorescent lights and HID lights – 6 to 12 inches above the plant
- LED lights – 6 inches above the plant.
For timing, all plants should have at least 12-hours of daily full light coverage. That can be extended to as long as 18-hours and even 24/7 for succulents.
Any flowering plant will need about 16 hours of light per day. Remember too, every plant needs its downtime.
When they’re under light, photosynthesis can happen. The downtime is when they use that energy for respiration. All that water, air and light needs put to good use.
That happens when the plant gets to rest as it puts the energy into releasing oxygen back into the environment, and it’ll help it flower too.
The One Tool You Can Use to Know if Your Plants are Getting Enough Light Exposure
Using artificial lighting to grow plants indoors has a specific advantage to any other, provided you use the right type of light, with the appropriate steps taken to get rid of unwanted heat. It has to do with the light spectra plants get.
The term used to measure this is Photosynethically Active Radiation time. It’s highest is in the summer months around noon.
For photosynthesis to happen, the UV rays have no impact. The only useable light for plants are nanometers between 300nm and 700nm. Knowing that is one thing; using it is another.
That’s where PAR meters come into the equation. It’s the one tool indoor growers can use to find out if the light equivalent of an entire grow area of their plants is getting the right amount of light. With it, light readings are reported as measures of micromoles per square meter.
Here’s the thing though, light measuring instruments can be one of many. Lux, Lumens, or even foot-candles. None of them tell you if your plant’s getting the right amount of light because it’s the photons from the light that needs to be measured.
So, forget Lux meters, and other instruments. It’s a PAR meter that tells you exactly what useable light your plants are getting.
There are guidelines for different types of plants and crops. Those use a Daily Light Integral (DLI), which only means the amount of PAR (useable light) a plant gets daily.
Take for example, growing your own lettuce at home. The ideal DLI is 14 to 16 moles per m2 per day. The only way to know if your lettuce was getting that is to use a PAR meter.
One distinct advantage indoor growers have using artificial light is the light is a fixed amount every second of every minute, every day. It’s not like greenhouse growers whose crops and plants are affected by seasonal changes and cloudy days.
The bulbs produce the same light intensity constantly and consistently. That gives you more PAR for longer, which also means, you can harvest crops year-round, and faster. Just imagine – fresh produce year-round, of any type.
Just adjust the light intensity to suit your growing stages. From flowering, to vegetation to harvesting your crops indoors…artificial lights can let you grow more and cost-efficiently too.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.