Grow Lights for Indoor Plants and Indoor Gardening: An Overview
Warm vs cool? "Full-spectrum?" LED, CFL, or HID? Here's what you need to know about mars grow light
for starting seeds, gardening inside, or houseplants.
Indoor growing offers many advantages. The biggest benefits are the most obvious: garden pests can't get at your plants, and you have total control over the weather.
Yet unless you're lucky enough to have a solarium or greenhouse attached to your home, providing sufficient light to your plants will likely be an obstacle (shade-tolerant houseplants excepted). South-facing windows may provide enough light for a tray or two of seedlings, but if you want to grow vegetables, or any other sun-loving plants, to maturity, you're going to need LED grow light bar
The indoor lighting found in most homes does little to support photosynthesis. Traditional incandescent bulbs do not have the proper spectrum of light, or intensity, to supplant the sun. Household fluorescent bulbs can make effective grow lights, but only if they are placed in within a few inches of the foliage and left on for 16 hours per day – not ideal.
When shopping for indoor led grow lights
, you'll notice they are labeled with numbers like 2700K or 4000K. This refers to their relative warmth or coolness on the color spectrum – the higher the number, the cooler the light. Foliage growth is generally best around 6500K, though many plants need a period of warmer light, around 3000K, in order to produce flowers, and thus fruit.
In other words, if your goal is to simply produce seedlings, leafy green vegetables, or root crops, you only need higher spectrum bulbs. If you want to grow flowers, marijuana, or any fruiting plant (cucumbers, tomatoes, peppers, lemons, etc.), you'll also require low spectrum bulbs. You can some types of bulbs are available in full-spectrum form, however, simplifying things.
The standard fluorescent bulb, commonly denoted T12, makes a decent grow light for houseplants, starting seeds, supplementing the natural light of a window, and other situations where lighting needs are modest. They are fairly weak in light intensity, however, and must be placed within a few inches of the foliage to have much of an effect.
, which are narrower in diameter than T12s (but still widely available wherever lightbulbs are sold), have a much higher light intensity, making them suitable as a sole light source for sun-loving plants. Compact fluorescent bulbs (CFLs) are an option for small spaces, or if you don't like the look of long rectangular fluorescent light fixtures – CFLs will screw into an ordinary incandescent light fixture.
Look for specialized full-spectrum fluorescent grow bulbs (like this , or , which fits into a standard socket) to provide the right balance of light for flowering plants.
While they are considerably more expensive than fluorescent bulbs, LEDs use half the electricity and last five times longer, more than paying for themselves in the long run. The average LED bulb from the hardware store is not designed for plant growth, however – you need special , a relatively new technology that is increasingly available from horticultural suppliers.
LED grow bulbs are capable of much greater light intensity than fluorescent bulbs and are available in full-spectrum form. An easy rule of thumb: Fluorescent bulbs are often used when growing just a handful of plants; LEDs are preferable for larger quantities since you can achieve higher light intensity per square foot. Another advantage of LEDs? They produce very little heat compared to other bulbs – an issue that can become problematic when you have a lot of lights in a small space.
HID Grow Lights
Before the advent of LED grow lights, were the main option for large indoor plantings. They are extremely powerful, but are expensive to purchase, consume electricity inefficiently, require special light fixtures, and give off a lot of heat. All that said, they are very effective and are still widely used. If you want to grow large plants like tomatoes or lemon bushes, HIDs are good bet because the light penetrates farther into the foliage than with other bulbs.
There are two types of HID bulbs. High-pressure sodium (HPS) bulbs are best for flowering (low spectrum), while MH (metal halide) bulbs are required to support vegetative growth (high spectrum); the two types are often used in conjunction. Unfortunately, each type requires its own fixture.
How to Install Weed Grow Lights
Installation requirements vary drastically depending on the scope of your indoor garden and the type of bulb used. But here are a few basic steps to get you started.
Figure out how many bulbs you need.
Most edible plants require at least 30 watts per square foot, but fruiting species (like tomatoes) generally won't produce abundant high-quality crops without 40 to 50 watts per square foot. Wattage is always indicated on the bulb package. Simply multiply the square footage of your growing area by the number of watts you plan to provide (between 30 and 50); then divide by the number of watts supplied by the bulbs you plan to use.
Devise a light rack.
You'll need a way to support the bulbs over the plants at the proper height. And unless you're growing something that will remain at more or less the same height throughout its lifespan, you'll also need a way to raise the light rack as the plants grow. This is usually accomplished through some sort of pulley system or by hanging the light fixtures with metal chain – that way you can easily adjust the height by changing the link the light fixture is home from. are also available for purchase online.
Add the necessary accoutrements.
It is generally wise to plug your lights into a timer to ensure they get the proper amount of light, and that they get it at the same time each day. are available for indoor growing, though a standard also works. If your lights bring the temperature above 80 degrees or so in your growing area, install a ventilation system to prevent heat stress. Aficionados make use of reflectors and all sorts of other grow light accessories to achieve optimum results.
How Long Should I Leave Grow Lights On?
Plants grown indoors require more hours of light than those grown outdoors. 14 to 18 hours of light per day is recommended for most edible species when grown under artificial lighting. Don't be tempted to leave the lights on 24-7, however – at least six hours of darkness each day is essential to plant health.
As the plants grow, raise the light fixture accordingly to maintain the optimal distance, which varies depending on the type of bulb used and its wattage (the higher the wattage.
As a self-confessed science geek I am fascinated by technology. Yet in the world of gardening this is often synonymous with the gimmicky (fibreglass meerkat solar light, anyone?) or the hugely complex and costly – think hydroponic growers that require a degree in electrical engineering to install. So it was with trepidation that I started experimenting with vegetable grow light
last winter in my tiny flat.
Nine months down the line I am a total convert, eulogising about them to all my gardening mates. They are something I feel could be a gamechanger to many modern gardeners, if we could only get over our preconceptions. This is why…
Once upon a time grow lamps were massive, ungainly things – fluorescent tubes more than a metre long that required complex and hideous systems of stands, cables and reflectors. They were real power guzzlers, too, so not exactly great for the planet, or your wallet – which would already have taken a pretty eye-watering hit from the price of all the kit. They even kicked out quite a bit of heat, which apart from raising safety issues, could also damage the very plants you were trying to grow.
However, recent breakthroughs in LED technology have created a new generation of effective, cool-running grow lights that cost a fraction of the old-school behemoths both to buy and to run, consuming (according to some manufacturers) 90% less energy. Crucially, they have shrunk down enough to be easily incorporated into average living room decor, some seamlessly integrated into planter-cum-lamp designs.
Others are light and thin enough to be fixed pretty much invisibly into standard flat-pack shelves, turning existing pieces of furniture in my house into instant growing units. These LED lights are becoming increasingly widely available online and even at a certain Scandinavian home store.
But why bother in the first place? Surely part of the pleasure of getting out in the garden is to escape the relentless march of technology into every aspect of our lives. Well, here's what my little experiment has done for me: I was able to grow houseplants in parts of my dark, urban flat that I never could before. This is a huge bonus to an obsessive plant collector like me, and could make an even more dramatic difference to houseplant lovers in basement or north-facing flats where lack of light is a serious issue.
Also, come spring seed sowing, I started off a good six weeks or so earlier and got zero etiolation on my baby plants. Stronger plants, much earlier, meant I got a bumper harvest of tomatoes and chillies weeks ahead of time. And all of this for the cost of a couple of desk lamps than run on minimal power. Brilliant!
Tens of millions have placed their trust in the Guardian's high-impact journalism since we started publishing 200 years ago, turning to us in moments of crisis, uncertainty, solidarity and hope. More than 1.5 million readers, from 180 countries, have recently taken the step to support us financially – keeping us open to all, and fiercely independent.
With no shareholders or billionaire owner, we can set our own agenda and provide trustworthy journalism that's free from commercial and political influence, offering a counterweight to the spread of misinformation. When it's never mattered more, we can investigate and challenge without fear or favour.
Unlike many others, Guardian journalism is available for everyone to read, regardless of what they can afford to pay. We do this because we believe in information equality. Greater numbers of people can keep track of global events, understand their impact on people and communities, and become inspired to take meaningful action.
We aim to offer readers a comprehensive, international perspective on critical events shaping our world – from the Black Lives Matter movement, to the new American administration, Brexit, and the world's slow emergence from a global pandemic. We are committed to upholding our reputation for urgent, powerful reporting on the climate emergency, and made the decision to reject advertising from fossil fuel companies, divest from the oil and gas industries, and set a course to achieve net zero emissions by 2030.
If there were ever a time to join us, it is now. Every contribution, however big or small, powers our journalism and sustains our future. Support the Guardian from as little as $1 – it only takes a minute. If you can, please consider supporting us with a regular amount each month. Thank you.