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If your homegrown micros look pale, or leggy, chances are, they’re not getting enough light. The world of lighting requirements is full of confusing terms and numbers. When you’re new to indoor growing all this can be overwhelming. Let’s try to clear the cobwebs together!
There are many types of lights available. But LEDs are overtaking fluorescents in recent years as the popular choice for indoor growing.
With a short growth cycle compared to other plants, it’s important to tailor an LED light for microgreens to these unique needs. Most of its energy is directed at producing tiny seedlings. Blue or blue-green lights work well at this stage of growth. Aim for bright lights between 5,000 and 7,000K to promote healthy growth.
Let’s explore how to choose the best LED light for microgreens, pros and cons of LEDs, and other lighting requirements so you can grow green, lush micros.
Note: This article is geared for the home grower or hobbyist. If you have a microgreens business, then your lighting requirements would be different.
Signs you need an artificial light for indoor microgreens
When microgreens don’t receive enough light, they exhibit the following telltale signs:¹
- Pale coloring: A lack of lighting means chlorophyll production isn’t kicking in, which results in yellowish (rather than green) coloring.
- Weak or leggy stems: Plants with insufficient lighting develop long, “leggy” stems which are desperately trying to reach for the sun. Unlike healthy stems, these are thinner and may fall over.
- Lack of leaves: Small leaves, or lack of leaf development altogether? Chalk it up to weak lighting (or perhaps insufficient nutrients).
Note: Conversely, some micros may receive too much light. Symptoms of this include scorched or burnt leaves, or bleached leaves.
Daily light requirements for microgreens
The right amount of light is important to growing flourishing microgreens. So how much light do microgreens need, really? According to the book Microgreen Garden: Indoor Grower’s Guide to Gourmet Greens by Mark Matthew Braunstein, aim for a combined total of at least 10 hours of light (natural light and/or artificial lighting) a day. Micros also need at least 6 hours of darkness.
If you have a sunny, south-facing window, you might have enough lighting without the need for supplemental lighting. Nothing beats the power of natural sunlight for growing healthy seedlings.
Keep in mind that winter daylight is shorter and provides weaker lighting than that of summertime.
You might need to use a combination of sunlight and LEDs to light your microgreens during the colder months.
Some types of microgreens like indirect lighting
Indirect lighting can be described as low to medium light. You can adjust your light treatments to suit the needs of the type of micros you’re growing.
Is keeping the lights on 24/7 a good idea?
More is not always better. The dark period each day is vital for plants to metabolize carbs/starches into plant growth, develop strong roots, grow thicker stems, and produce more lush leaves.²
Leaving an LED light for microgreens on 24/7may lead to visibly larger growth, but this doesn’t equate to better quality growth.
Light quality can affect the taste of microgreens. Those that have received the proper amount of illumination will have a sweeter taste, while those with 24/7 lighting may taste either bitter or have an “off” flavor.
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Keep your lighting system simple
If you’re simply growing a tray (or two) of microgreens at home for yourself, you don’t need a fancy setup. Any supplemental light bulb (even a cool white fluorescent light or incandescent bulb will work).
When you’re just starting out, make use of what supplies you already have at hand. If you have fluorescent bulbs or light tubes such as a T5 or T8, use those.
However, if you’re planning on buying new lighting, LED lights are a good choice as we’ll examine in the sections below.
What’s the difference between a regular light and a grow light?
There are regular LED bulbs that you can pick up at any home improvement store, then there are LED grow lights. So, is there any difference between the two?
LED refers to any lighting system that uses light-emitting diodes. Regular LED bulbs are designed to simply illuminate a room or space. On the other hand, LED grow lights provide full light spectrum for optimal growth of plants.
Grow lights are more expensive than regular LED lights.
Do you need special grow lights for microgreens?
Simply put, special grow lights are not necessary for growing a simple tray of microgreens at home (especially if your micros receive a few hours of natural sun each day). You could use a regular LED light bulb and still get similar results.
(Remember that micros have such a short growing cycle that they’re not subject to the same lighting demands as other mature plants.)
But, grow lights are definitely nice to have if you plan on doing other kinds of indoor growing where plants grow to full size, or flower. And, having proper grow lights will provide your microgreens with all the lighting requirements they’ll need.
Common lighting definitions
Confused with all the different lighting terms out there? Let’s look at a few common definitions.
- PPF (photosynthetic photon flux): This measures the amount of light that’s actually usable by a plant. When light is released by a bulb, it’s measured as micromoles of light per meter per second (umol m-2s-1). Another similar term is PPFD (photosynthetic photon flux density) which measures when PPF contacts the surface of the plant. The PPFD measurement decreases as the light source moves further away from the plant. Most grow lights have a PPF between 10 and 50—the higher the better (typically) for micros and seedlings.³
- Kelvin (K): A measure of the color temperature or color of the light produced. It ranges from 1,000 (warm/red light) to 10,000 (cool/blue light).⁴
- Lumens: This measurement determines the brightness of the light as it hits the human eye. But in the world of plants this is less important as it doesn’t account for other light wavelengths that affect plant growth.
- Watts: This indicates the amount of energy used to create light. It’s not really an indicator of any light intensity. High-efficiency bulbs can produce more light using fewer watts.
Pros and cons of LED lights
There are many types of lighting to choose from. Incandescent light was once popular, but fell out of favor as they produce a lot of heat, and aren’t durable. Next came fluorescent lights which are cheaper than LEDs, but less efficient and don’t last as long as LEDs.
There are also high-pressure sodium and metal halide lights. Due to their larger size and cost, these are better suited to larger growing operations, not the average home grower.
Let’s take a closer look at the pros and cons of LED lights.
Pros of LEDs
- Longer lasting: LEDs are hands-down longer lasting than fluorescent bulbs. Some last up to 45,000 hours so you won’t have to worry about them burning out any time soon!
- Produces less heat: Unlike old incandescent or fluorescent lighting, LEDs produce very little heat producing a safer growing environment (especially in smaller spaces).
- Energy efficient: Less energy usage helps keep electricity bills low.
- Wide spectrum of colors available: The color of lighting is important depending on the stage of plant growth. Colors run the gamut from cool to warm, including a balanced white light.
Cons of LEDs
- Costs more upfront: While the initial costs of LEDs are higher than regular incandescent or fluorescent lighting, it makes up for it over time. Since LEDs last so long, they more than make up their cost over the years. With emerging technology, the cost of LEDs is only going down.
Look for these qualities when buying an LED light for microgreens
When choosing a microgreen grow light, look for the following:
- Choose a full spectrum light with a color temperature within the blue scale, or blue-green (between 5,000 to 7,000K) to promote healthy seedling growth. A balanced light also works well for all stages of growth.
- Look for a lumens measurement as close to natural daylight as possible (between 2,000 to 3,000).
- Watts of 20 or higher.
- A PPF between 250 to 450 umol m-2s-1.
Did you know. . . Plants use more blue-green light when they are young seedlings (or micros), and more red light as they flower and make seeds. Since micros are harvested before they flower, blue and blue-green lights are more useful.
Distance between lights and microgreens
How far should you place your light from your tray of microgreens? Generally, microgreens grow well anywhere between 6 to 12 inches (15 to 30 centimeters) from an artificial light. You can easily prop up your grow tray with a book or box to bring it closer to the light.
Other lighting considerations and tips
Here are a few other things to consider when buying LED grow lights for microgreens:
- Grow area: The size of your grow area will determine how many lights to buy, as well as the types of fixtures you’ll need. For a single tray, you could use a simple clip-on fixture. For multiple trays, you may need a tube light.
- Use a timer: To keep your electricity bill low, use a timer. If your tray receives roughly 5 hours of natural sun each day, then you can schedule your grow lights to turn on at dusk for another 5 hours to get the recommended 10 hours of light each day.
- Color temperature can affect growth and nutrients: Agriculture and Agri-Food Canada (AAFC) scientists discovered that the light color can affect the growth of Brassica microgreens. Researchers found that boosting amber-blue light and reducing red lights led to higher levels of carotenoid production (a precursor to vitamin A) in Brassica micros.⁵
At what stage do microgreens need light?
During germination, most plants don’t need any light. Many micros growers use the term “blackout phase” for this initial stage of growth. However, once young shoots have emerged and are showing steady growth, it’s time to expose the seedlings to light.
👉If you like this post, see our Complete Guide to Growing Microgreens at Home.
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- University of Minnesota Extension, Lighting for indoor plants and starting seeds, https://extension.umn.edu/planting-and-growing-guides/lighting-indoor-plants. Accessed January 2023.
- Braunstein, Mark Matthew (2013). Microgreen Garden: Indoor Grower’s Guide to Gourmet Greens. Book Publishing Company. ISBN 13: 978-1-57067-294-1.
- University of Minnesota Extension, What type of grow lights should you use for starting seeds?, https://extension.umn.edu/yard-and-garden-news/grow-lights-starting-seeds. Accessed January 2023.
- Johnny’s Selected Seeds, Guide to Choosing a Grow Light, https://www.johnnyseeds.com/on/demandware.static/-/Library-Sites-JSSSharedLibrary/default/dw818e2afc/assets/information/grow-light-guide.pdf. Accessed January 2023.
- Agriculture and Agri-Food Canada, Lights, Colour, Nutrients! LEDs play a starring role in improving nutritional quality of plants, https://agriculture.canada.ca/en/news-agriculture-and-agri-food-canada/scientific-achievements-agriculture/lights-colour-nutrients-leds-play-starring-role-improving-nutritional-quality-plants. Accessed January 2023.