Grow Lights for Microgreens: Which Light Color Works Best, Based on a Study of 21 Varieties
What grow lights do microgreens need? For an indoor shelf, white, full spectrum LED lights. A university study that grew 21 microgreen varieties under red, blue and white LEDs found that white light gave the highest average plant weight in most varieties, while blue light raised flavonoid and anthocyanin levels but slowed growth. At MP Seeds we recommend running white LEDs 12-18 hours a day, about 20-25 cm above the microgreens, with 30-60 W of lamps per 1 m shelf. If you want a ready-made option, our full spectrum LED grow light is built for exactly this.
Thanks to our friend Lucia Jasenovska and her study of microgreens, we know much more today about how different light colors affect microgreens. Lucia and her colleagues at the Slovak University of Agriculture in Nitra grew microgreens from MP SEEDS seeds under three types of LED light and measured their weight and pigments. We want to thank her for using our seeds, running the experiment and adding so much value to the microgreens world. Thank you, Lucia! Below we turn the results into practical answers: which light to use, for how long, how high and how strong, followed by the full results of the study.
Table of Contents
1. What grow lights do microgreens need?
For an indoor microgreens shelf, we recommend white, full spectrum LED light: in the study below it gave heavier plants than red or blue light alone in most varieties. Light controls how fast microgreens grow, how much they weigh, what color they turn and how many nutrients they build. Microgreens are usually grown indoors, on shelves or in grow rooms, so the lamp replaces the sun. Most growers use LED lights today: they are easy to find, affordable, simple to use and energy efficient, and they let you grow all year round in a small space.
LED grow lights come in three main types:
- White, full spectrum LEDs (bars, tubes or shop lights): white light that covers the whole visible range, including blue and red. This is what most microgreen growers use.
- Red and blue LEDs (the purple-looking "blurple" lamps): only red and blue diodes. Plants use red and blue light well. The study below compared white light with red alone and blue alone, not with a red and blue mix, so it does not settle that comparison.
- Single-color LEDs: pure red or pure blue, used in research or to add one color to a white lamp.
If you compare white lamps, our homemade lamp used cool white LEDs of 5000-6500 K, while the study used warm-white LEDs; the study did not test which color temperature is best.
2. Which light color is best for microgreens?
For microgreens, white light is the best color for most varieties. In the study, plants under white LEDs were generally the heaviest, plants under red LEDs came second and plants under blue LEDs were the lightest; white LEDs also had a positive effect on most other measured traits. Blue light, on the other hand, gave the highest levels of flavonoids and anthocyanins, the pigments behind antioxidant value and red or purple color, but it slowed growth.
A few varieties behaved differently: Red Opal basil, kale and mizuna grew better under blue light than under white, and mustard had its highest average weight under red light. So there is no single perfect color for every crop, but white light is the safe choice for a mixed shelf.
In our opinion the best match for a microgreens farm is a white LED lamp, or a white lamp with some extra blue: white light keeps the plant weight high, and in some varieties, such as lettuce, kale and beets, it produced flavonoid levels similar to those produced by blue light. In other varieties blue light gave clearly more flavonoids, so white light is a compromise between weight and these compounds. The detailed results are in sections 8-10.
3. How many hours of light do microgreens need?
At MP Seeds we generally recommend 12-18 hours of light per day, because the right duration depends on the variety and growing conditions. The study used 14 hours of light and 10 hours of darkness, which falls inside this range. The University of Maryland Extension suggests about 16 hours of light a day, and the Utah State University Extension keeps grow lights on for 18 hours and off for 6.
Plug your lights into a simple timer, so the microgreens get the same schedule every day. During the first days after sowing the trays usually stay covered in the dark; we explain how long in our guide to germination and blackout days. Turn the lights on when you uncover the trays.
4. How far should grow lights be from microgreens?
We hang our LED lamps about 20-25 cm above the microgreens for most varieties: a little lower for fast-growing herbs and a little higher for heat-sensitive crops. The University of Maryland Extension suggests 6-12 inches (15-30 cm) above the plants, depending on how strong the fixture is. A stronger lamp can hang higher; a weaker one needs to be closer.
Check that the leaves do not get warm. Hanging the lamp on chains or adjustable hooks lets you raise it as the crop grows. If you are choosing trays for the shelf, our guide to microgreen trays compares the sizes.
5. How strong should the light be?
Watts tell you how much electricity a lamp uses; PPFD tells you how much light, in µmol/m²/s, reaches the plants. For a 1 m shelf we recommend lamps with 30-60 W in total, depending on how densely you sow and how high the lamps hang. One 33 W LED bar or a homemade lamp with 30 one-watt LEDs sits at the lower end of that range.
If you want to compare lamps by numbers, look at PPFD. In the study the light in all three chambers had a similar energy of about 60 W/m² (light energy reaching the plants, not the electrical power of the lamps), which gave a PPFD of about 160 µmol/m²/s under blue, about 175 under white and up to about 200 under red light. These are the conditions of the experiment, not a proven optimum. According to its specification, our 33 W LED bar reaches a PPFD of 220 µmol/m²/s when three bars are mounted per row; one bar alone gives less. PPFD depends on the height and area of the measurement, which the specification does not state, so use this figure as a guide rather than for exact comparisons.
6. Signs your microgreens get the wrong light
These signs are reasons to check your lighting, not a certain diagnosis:
- Pale, leggy, stretched microgreens: often too little light, or the lamp hangs too high. A weak decorative bulb gives pale, leggy shoots. Move the lamp closer or add another one.
- Small, light plants under a colored lamp: in the study, blue light alone made many varieties much lighter (amaranth under blue weighed about a fifth of its weight under white). Switch to white, full spectrum light.
- Uneven growth across the tray: possibly uneven light. Space the LEDs or bars evenly and keep the whole tray under the lamp.
- Warm leaves: the lamp may be too close. Raise it a few centimeters.
7. The study: how the experiment was done
The study looked at how red, blue and white LED light affects the growth and pigment composition of microgreens, including a non-invasive measurement of anthocyanins and flavonoids. Some effects of light color were already known, but there was little information about how different species and varieties respond.
Conditions:
- February to June 2023, at the Institute of Plant and Environmental Sciences of the Slovak University of Agriculture in Nitra (IPES SUA Nitra), Slovakia.
- Growth chamber with controlled and recorded conditions: 23°C during the day, 20°C at night, humidity 60-80%.
- MP SEEDS seeds were used in the experiment. Each variety was split and grown under each light.
- Three types of LED light: polychromatic warm-white LEDs, monochromatic red LEDs (peak at 660 nm) and monochromatic blue LEDs (peak at 470 nm).
- Similar light energy in all three compartments, about 60 W/m², which means a PPFD of about 160 µmol/m²/s for blue, about 175 for white and up to about 200 for red light. The energy was equal, so the number of light particles (PPFD) differed slightly between the colors.
- 14 hours of light and 10 hours of darkness.
- Plants grown individually in 0.5 l pots with peat substrate, four pots per variety under each light.
Varieties tested (21): amaranth, red cabbage, kohlrabi, arugula, lettuce, cress, radish Red Rambo, radish Rose, mustard, spinach, fenugreek, pak choi, mizuna, komatsuna, kale, broccoli, red beet, yellow beet, Italian basil, Red Opal basil and onion.
What was measured:
- Fresh and dry weight. At the end of each growing cycle the researchers weighed individual plants right away (fresh weight), then dried them in paper bags in an oven at 75°C for 2 days until the weight stopped changing (dry weight).
- Pigments. Samples were frozen at -81°C, extracted in acetone, diluted with 80% acetone and measured with a spectrophotometer to calculate chlorophyll and carotenoid content.
- Fluorescence ratios. A multispectral fluorimeter measured the plants from above without touching them. In plain words: the FER R/UV ratio estimates flavonoid content, the FER R/G ratio estimates anthocyanin content, and the SFR ratio estimates chlorophyll in the leaf surface. These ratios have no unit; a higher number means more of the compound.
8. Results: fresh weight under white, red and blue light
Fresh weight matters most for a microgreens business, because it decides how much you harvest and sell. The chart below shows the average results for all varieties: each x is the mean, the line is the median and the box covers the middle half of the values.
Source: Jasenovska et al. (2024), Folia Horticulturae, Figure 2. (A) fresh weight per plant, (B) total chlorophyll, (C) total carotenoids, (D) FER R/UV, linked to flavonoids, (E) FER R/G, linked to anthocyanins, (F) SFR.
Microgreens grown under white light were the heaviest, followed by those grown under red light and then those grown under blue light. Examples from the experiment:
- Amaranth under blue light weighed almost 5 times less than under white light (blue 0.51 g, red 1.45 g, white 2.44 g per plant).
- Radish Red Rambo under white light weighed more than twice as much as under blue light (white 5.33 g, blue 2.43 g).
- Cress grew heaviest under white light and lightest under blue light (white 3.00 g, red 1.83 g, blue 0.66 g).
- Pak choi weighed almost the same under red and white light, and less under blue light (white 2.00 g, red 1.99 g, blue 1.30 g).
The table shows the average fresh weight per plant, in grams, for all 21 varieties. The highest average for each variety is in bold; small differences are not always statistically significant.
According to the authors, white light gave significantly higher growth than both red and blue light in amaranth, kohlrabi, radish, cress, both beets and broccoli. Red light was the best for mustard, and blue light supported the growth of red basil, kale and mizuna. In onion the differences were not significant. Blue light reduced growth compared with white and red light in many species, including amaranth, mustard, kohlrabi, cabbage, radish, arugula, fenugreek, spinach, cress and pak choi.
In short: white LED light generally produced the heaviest plants in the experiment, which makes it the best choice for weight. Blue LED light makes microgreens of "higher quality" in terms of some nutritional compounds, but slows their growth.
9. Results: flavonoids and anthocyanins
Flavonoids and anthocyanins are natural compounds in plants, including microgreens. Their content can be a competitive advantage, especially as the microgreens market becomes more crowded, and it depends partly on the color of the light the microgreens grow under.
- Flavonoids are antioxidants found in fruits, vegetables and herbs. In plants they protect against environmental stress, and they are widely studied for their effects on human health.
- Anthocyanins are a group of flavonoids that give the red, purple and blue colors to many fruits and vegetables, and they also act as antioxidants.
Flavonoids. Earlier studies had already shown more phenolic compounds under blue LED light, for example in Chinese kale and buckwheat sprouts. In this experiment, blue light gave the highest flavonoid ratio in most varieties, followed by white and then red light. Examples (FER R/UV ratio, no unit):
- Mizuna: blue 1.59, white 1.58, red 1.37.
- Kale: white 1.09, blue 1.07, red 0.99.
- Amaranth: blue 1.08, white 1.02, red 0.96.
- Red beet: blue 1.24, white 1.22, red 1.06.
- Red cabbage: blue 1.37, white 1.23, red 1.14.
In some species, such as lettuce, kale and beets, white light, which also contains blue, was enough to reach the same flavonoid level as blue light. Blue light generally raises flavonoids more than red or white light, although some species respond differently.
Anthocyanins. Light color affects anthocyanins in a similar way, with some differences. In green-leafed microgreens, blue light mostly increased anthocyanins, which is linked to the blue light receptors in plants. Red-leafed species varied more:
- Amaranth (red-leafed) showed a clear increase under blue light: FER R/G ratio blue 2.48, white 2.14, red 1.95.
- Other red-leafed varieties responded in different directions. Mizuna and red basil did not show the expected increase under blue light, which the authors say needs further study.
- Green-leafed varieties: blue light mostly increased anthocyanins; in mustard, blue light did not raise them above the level under white light.
- Radish, onion and broccoli did not respond to light color with more anthocyanins.
Photo: red amaranth and Red Giant mustard grown under blue (B), red (R) and white (W) light.
10. Results: chlorophyll and carotenoids
Chlorophyll and carotenoid responses depended on the variety. Across the 21 varieties, white light gave the highest average content of both, while blue and red light were close to each other; in kale, red beet and basil, red light gave the most chlorophyll. Earlier research explains part of this: blue light supports the genes involved in chlorophyll production, while strong red light can lower the precursors of chlorophyll. Examples (total chlorophyll, mg per g of leaves):
- Mizuna: blue 0.80, white 0.80, red 0.78.
- Kale: red 0.59, white 0.57, blue 0.43.
- Amaranth: white 1.81, red 1.34, blue 1.15.
- Red beet: red 0.62, white 0.60, blue 0.48.
- Red cabbage: white 0.85, blue 0.80, red 0.61.
Carotenoids followed a similar trend to chlorophyll. Other studies have found that blue light raises carotenoids in lettuce but not in spinach, so the effect depends on the plant. Faster growth under white and red light can also cause a dilution effect: the plant grows faster than it builds pigments, so the pigment content per gram is lower. According to the authors, this may partly explain why slower-growing plants under blue light show higher concentrations.
11. What the study found
- Light color clearly affects the growth and pigment content of microgreens.
- Across 21 varieties grown under red, blue and white LEDs, white light generally gave a higher fresh weight than single-color light, especially compared with blue light.
- White, broad-spectrum LEDs supported the best growth and had a positive effect on most measured traits, which shows the advantage of white LEDs over single-color red or blue LEDs.
- Some varieties grew better under blue light than under white (Red Opal basil, kale and mizuna), and mustard had its highest weight under red light.
- Changing the light color can improve both the quantity and the quality of microgreens, especially their flavonoid and anthocyanin content, but the response depends on the variety, so the best light can differ from crop to crop.
- Chlorophyll and carotenoids depended on the variety; across all 21 varieties, the averages were highest under white light.
- Blue light was especially effective at raising flavonoids and anthocyanins, but it sometimes reduced growth.
What this means for your setup (our recommendation): use white, full spectrum LEDs for a mixed microgreens shelf. In the study, white light gave the highest average plant weight in most varieties, and white light also contains blue. Avoid lamps with only red or only blue diodes. If you grow mostly kale, mizuna or Red Opal basil, their response to blue light is worth testing on your own shelf; the study did not test mixes of white and blue.
12. Which grow light to choose
You have two practical options for a microgreens shelf.
A ready-made LED bar. Our full spectrum LED grow light is a 33 W bar, 900 mm long, with an IP65 housing for humid grow rooms. It runs on 100-277 V AC, gives a PPFD of 220 µmol/m²/s with three bars per row, and one connecting cable links up to 6 bars to a single socket. It comes in packs of 2, 10 or 25, with clips, screws and cables. One bar running 12-18 hours a day uses about 0.4-0.6 kWh (33 W × hours; your cost depends on your electricity rate).
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A lamp you build yourself. If you like electronics and want to choose the LED colors yourself, our guide to building a DIY LED grow light for microgreens shows the parts, costs and assembly step by step.
FAQ
Do microgreens need light?
Yes. After the first few days in the dark (the blackout period), microgreens need light to turn green and grow. Without enough light they stay pale and stretch. We recommend 12-18 hours of light a day from a white LED lamp.
What kind of light setup do I need to grow microgreens?
We recommend a shelf with white, full spectrum LED bars or tubes about 20-25 cm above the microgreens, 30-60 W of lamps per 1 m shelf and a timer set to 12-18 hours a day.
Do I need a special grow light, or will any white LED work?
Plants use most of the visible light, so a bright white LED can grow microgreens. What matters is enough light for long enough; a weak decorative bulb gives pale, leggy shoots. A grow light bar like ours adds a stated power of 33 W, an IP65 housing for humid rooms and easy mounting over a shelf.
Is red or blue light better for microgreens?
Neither on its own. In the study, red light gave heavier plants than blue light, and blue light gave more flavonoids and anthocyanins, but white light gave the highest average weight in most varieties while still containing blue light.
Are full spectrum lights better than red and blue grow lights for microgreens?
The study compared white light with red alone and with blue alone: white broad-spectrum LEDs gave a higher average fresh weight than either single color in most of the 21 varieties. It did not test lamps that mix red and blue diodes, so it does not answer that comparison directly. We recommend white, full spectrum LEDs.
How much light intensity do microgreens need?
The study grew microgreens at a PPFD of about 160-200 µmol/m²/s, with 14 hours of light a day; these were its test conditions, not a proven minimum. In practice, MP Seeds recommends 30-60 W of LED lamps per 1 m shelf, hung about 20-25 cm above the microgreens.
Summary
For microgreens, use white, full spectrum LED grow lights. A study conducted at the Slovak University of Agriculture in Nitra using 21 microgreen varieties grown from MP SEEDS seeds found that white LEDs gave the highest average plant weight in most varieties, while blue light raised flavonoids and anthocyanins but slowed growth. At MP Seeds we recommend running the lights 12-18 hours a day on a timer, about 20-25 cm above the microgreens, with 30-60 W per 1 m shelf. Lamps, trays and everything else for a microgreens shelf are in our supplies for growing microgreens.
Sources and Further Reading:
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