90 Second Intro to Plant-Light Science
There are a couple of simple concepts that take the guesswork out of lighting for indoor growing. Knowing this stuff will let you cut through the hype and pseudo-science to confidently pick just the grow lights you need.
Plants Eat Light
All plants need light for the same reason: It’s their source of energy. Light falling on leaves is converted into sugars. Sugars that feed the plant. That’s photosynthesis.
For growing herbs and vegetables indoors providing enough light is job number one. That seems simple enough but… How do you know how much light is enough?
How Light-Hungry is Your Plant?
Every variety of plant needs a certain amount of light to thrive.
Mint will grow happily in moderate light. Hot peppers need intense light to grow well.
Those descriptions are pretty vague though. Not a lot of help when we’re trying to setup a productive indoor garden.
Luckily for us science tells us exactly how much light each plant needs.
The key is DLI — Daily Light Integral. DLI is a measurement of exactly how much light a plant needs each day to grow its best. You can think of DLI as calories for plants.
Mint has a DLI of 10. Hot peppers have a DLI of 20. Just like you’d guess, that means that hot peppers will need twice as much light as mint to grow well.
Matching Grow Lights to Plants
Once you know the DLI needs of a plant you can precisely match a grow light setup to provide that DLI.
The DLI a grow light provides is defined by three things:
- Intensity of the light.
- Distance from the light to the plant.
- Number of hours in the day the light is on.
We’ve Got the Light Information You Need
At BrightGrow.co we’re creating a easy-to-use library of all the DLI information you need.
In our plant library you’ll find the DLI needs for all kinds of vegetables and herbs. Plus we match each plant to ideal grow light setups. So you can get the right setup first time.
Mint is one of my favourite herbs to grow under lights. There are loads of unique varieties to choose from — from classic spearmint to varieties with hints of citrus or lavender.
Mint isn’t very demanding for light. It can grow on a bright windowsill — but will often stretch out and grow smaller leaves in the search for more light.
Growing under LED or fluorescent grow lights will help you grow a bushy mint plant that produces for a long time.
Mint has a DLI requirement between 10 and 16. See our recommendations for ideal grow light setups for mint >>
You can propagate mint from seeds or cuttings. Cuttings are a great way to get started — they feel like you’re getting something-for-nothing. Just snip a sprig from a store bought plant and submerge the lower half in water. Keep the cuttings in a bright space for a week or two and vigorous roots will grow from the cut stems.
Mint will grow in pretty much any container. Something wider than deep is a good idea — as the root systems spread out but don’t go very deep.
Radishes are fast growing, fairly compact and not too light-hungry. In many ways they’re the perfect indoor crop. There’s something sort of magical about pulling a ready-to-eat vegetable from the earth.
Radishes don’t need much space. You can grow multiple plants in one larger container with by 3-4 inches separation. Their roots don’t grow very deep — usually 6″ of soil is plenty.
In the proper growing environment radishes can be ready to harvest in 3-4 weeks. They’re add a nice spicy crunch to salads. I recently discovered roasted radishes and I love the flavour.
Radishes thrive with a light that provides DLI of 15+. Learn more here >>
Lettuce is one of the vegetables that grows best with grow lights. Plus there are lots of varieties to try. Generally anything but iceberg-style lettuce will grow well indoors.
I like to grow a few varieties at once. It takes just a minute or two to pick a fresh salad that looks just as good as it tastes.
Lettuce will continue growing after you pick outer leaves — giving you a regular harvest for weeks.
Lettuce is only moderately light-hungry and prefers to grow in cooler temperatures, 60-70°F is ideal.
Lettuce grows best under a light that provides 12-16 DLI. Learn about the ideal setup here. >>
Chilli peppers are very beginner-friendly. They grow easily and provide lots of flavour from compact plants. Choose a chilli variety that suits your palette — from mildly spicy right through to insanely hot.
Peppers prefer a consistently warm room to grow in. 65-90°F keeps them happy. They’re quite demanding for light so you will need a more intense grow light setup.
Also, like most fruiting plants, peppers benefit from a full-spectrum light that provides plenty of light in the red part of the spectrum. The light will still look white to human eyes — so you don’t have to have a garishly lit grow space.
Microgreens aren’t a particular plant — they’re a style of growing that works with many different plants. The basic plan is to seed a crop super-densely and harvest when the seedlings are just a week or two old.
Microgreens are a rewarding and simple indoor crop. Because they’re growing for such a short time you skip many complexities of longer cycle crops. No worries about fertilizer or pests or diseases because they’re ready to harvest before any of those issues can develop.
Microgreens don’t generally need much light. In fact some varieties, like sweetcorn, can be grown in the dark. Most varieties of microgreen develop the best flavour and color with some light though.
Understanding Grow Lights
Grow lights are an essential tool for any indoor gardener but… trying to find the right grow light it can feel like you’re in a bewildering jargon-filled maze.
We’ve done the research so you can pick just the right grow lights for the vegetables you want to grow.