Choosing a grow light is no easy task. Everyone has their own idea of what makes the best grow light. Some prefer expensive high-wattage full spectrum grow lights, while others say that cheap shop lights are just as good for microgreens. With research from botanists and actual microgreen growers, we have an answer for you…
The best microgreen grow light provides more blue, red, and far-red light while still providing sufficient light in the rest of the wavelengths from 260 to 850 nm. This balance of frequencies encourages sprouting, root growth, stem and leaf growth, as well as proper color and flavor.
It can be hard to know what advice to follow, as the advice is all over the board. So I set out to come up with an objective view of what makes the best microgreen grow light and to bring you the information you need to help you choose your lights. Here’s what you need to know…
Sufficient lighting to get the best results
Without sufficient lighting, microgreens will look pale. They won’t be able to develop chlorophyll and become that healthy green, or beautiful red, purple, and other colors that make microgreens so appealing. Even the flavor of the greens will suffer. Mold, fungus, and disease will also become more of an issue.
If you are in a greenhouse or have excellent natural lighting, that ambient light does the job. Curtis Stone, known as “The Urban Farmer,” maintained a large production of 400 flats a week using nothing but passive solar in a greenhouse.
That said, many of us (myself included) are growing indoors and need artificial lighting to keep our microgreens happy. Microgreens definitely need some additional light beyond the ambient indoor ceiling and window light.
How many watts are required to grow microgreens?
Microgreens need photons (light particles), not watts (electrical energy). But you can’t go online and buy a box of photons. Lights are specified and sold by watts or lumens. And you pay your electric bill based on how many watts your lights consume. As your microgreen operation grows, this bill can become substantial.
Stephane Lanteigne stated, “My electricity bill is roughly $5000 per month. Optimizing my lighting program saves me money by making sure I don’t waste electricity on plants that aren’t using the extra photons to grow.”
So it’s best to consider upfront how much wattage is actually required to grow microgreens. To that end, I polled microgreen growers to see what they have found as the optimum wattage required for a shelf of 4 10×20 trays of microgreens. Here’s how they responded…
- Most growers use 40 watts per shelf
- The average is 56 watts per shelf
- The median is 54 watts per shelf
- There were a significant number of growers using 60 or 80 watts per shelf.
What can we gather from this?
Don’t use less than 40 watts of lighting per shelf. Only one microgreen grower is using less. Likewise, using 80 watts or more may be overkill. If you are growing the plants for fuller vegetation, flowering, budding, or fruiting, this would merit a stronger light. But for the microgreen stage, you just don’t need as much light.
The average and median watts microgreen growers are using is between 50 and 60. Some big names in the microgreen industry also recommend this range. Donny Greens of Finest Foods NY suggests a 54-watt light. Nate Dodson of microgreensfarmer.com recommends 40 to 60 watts. And Curtis Stove, of FromTheField.tv, recommends a 64-watt fixture.
Since so many growers use 40 watts per shelf, you will probably get good results as well using 40 watts of lighting. If that’s the path you take, there are ways to maximize the value of a 40-watt lighting system.
How to get the most out of your microgreen grow lights
To get the most out of your grow lights, you want to improve the lux. Lux refers to how many lumens are hitting your plants, the light intensity on your microgreens. The higher the concentration of light on your plants, the higher the lux. And the happier the plants.
Think of it like a fire on a cold night. When you get closer to the fire, you feel warmer. The fire didn’t get more intense. But being closer allowed more of the heat energy to reach you and be absorbed by your skin.
Light energy works the same way. If you bring the lights closer to the microgreens, the lux value goes up. The plants receive more light energy and benefit more from it. Hence, you can get away with fewer watts (fewer lumens) simply by reducing the distance between the microgreens and the lights. Instead of 8 – 10 inches of separation, try 5 – 6 inches of separation.
Another trick to maximize the value of your grow lights is to use reflective shields to make sure the photons are directed toward your microgreens. Some grow lights have built-in reflectors to focus the light in the direction of the plants. You can also put a sheet of aluminum foil, or an aluminum plate under the shelf liner to reflect the light down to the trays.
Another trick is to drape mylar blankets on the front and back of the racks. This will bounce the light that would have escaped right back onto your plants. By funneling the light onto your microgreens, you can get more results with fewer watts.
What light frequencies do plants need?
Botanists have discovered that each light frequency plays a different role in plant growth and development. Here’s a breakdown of what each light frequency does for plants:
- UV-B light: Helps increase the darker colors in microgreens, like purple. It also inhibits the growth of fungus and pests.
- Blue light: Inhibits stem-stretching, promotes root development, improves aroma, flavor, and nutritional value, and drives peak chlorophyll pigment absorption.
- Green light: Excites chlorophyll molecule electrons deep within a leaf or lower in the plant canopy. Small amounts of green allow the plants to be more efficient at photosynthesis in bright light conditions. This can increase crop yields.
- Red light: stimulates photosynthesis and increases crop yields.
- Far-red light: counterbalances blue, promotes leaf expansion and improves photosynthesis. Works synergistically with red and blue when in the right ratios.
What is a full spectrum grow light?
Some people feel full spectrum means that it includes at least some of each light frequency in the range of 400 – 700 nm. Others feel that it represents the spectrum of natural daylight as closely as possible. But these definitions don’t tell the whole story. Here’s a more accurate definition.
Full-spectrum grow lights include all the light frequencies that plants respond to. High quality grow lights will include light beyond the typical PAR range of 400 – 700 nm. While strongest in blue and red, they will include balanced proportions of UV-B, green, and far-red.
What makes a balanced proportion of light colors is determined by what you are growing. If you are looking for true-leaf greens, flowering, budding, and fruiting, you will want to get grow lights designed for these stages of the plant life. In this article, we will focus on microgreens.
What type of light is best for microgreens?
Microgreens are harvested before the true-leaf stage. So their need for blue and far-red is not as significant as with other crops. They are mostly dependent on red, with a smaller balanced amount to blue, far-red, green, and UV.
You will find full spectrum grow lights that appear purple, with more photons in the blue and red frequencies. But a common question is, are “full-spectrum” purple grow lights just a marketing gimmick, or do they help microgreens? What type of lights do microgreen growers actually use and why?
I surveyed microgreen growers to see what types of grow lights they actually use. Here’s what I found…
What type of lights microgreen growers are using
Few microgreen growers are using full-spectrum purple grow lights. These purple lights are more commonly used for maturing plants beyond the microgreen stage, like flowering and fruiting. Michael Watson said, “I use white for my microgreens and red/blue for my leafy greens.”
Most growers are happy with simple white shop lights. They are using 5000K to 6500K color temp. And they are getting good results with these cheaper lights. Nate Dodson and Curtis Stone both recommend cheap white shop lights.
It’s worth noting that these white shop lights are not full spectrum. Just because it is white doesn’t mean it has all the spectrum that plants need. These white shop lights are typically heavier in yellow, green, and orange frequencies that have limited value to microgreens.
If you decide to go with shop lights, you will probably want to boost up the watts to 60-80 watts per shelf. That way you get the same amount of blue, red, and far-red photons you would have had with a 40-watt full-spectrum white light.
The poll also showed a significant number of microgreen growers using full-spectrum white lights. Many of these have seen yield and quality improvements by switching from shop lights to full spectrum.
“Full-spectrum grow lights will make your microgreens short and leafy, the shop lights make the sprouts grow tall, searching for that full-spectrum light.” – Jeremy Keefe
“I use the full spectrum LED when I want my reds to color-up on things like red kale. Otherwise, my greens do well under white fluorescent and led lights.” – JT Watts
But there is an elephant in the room that must be mentioned…
Full-spectrum white grow lights don’t all have the same wavelength distribution. Different full spectrum grow lights will perform differently. So when it comes to microgreens, here’s what you will want to look for…
What light spectrum do microgreens need?
A spectrum chart that’s heavy on the red: This is the workhorse for microgreen production. It will increase photosynthesis and build more bio-mass.
A good balance of blue and far-red: Most full spectrum grow lights contain little to no far-red photons. Look for spectrum charts that reach further into the 700+ range.
Enough mid-spectrum to make the light look white or near-white: This will provide sufficient green for the microgreens. The white light helps you spot any problems and correct them quickly. It is also better for our health. One grower said, “After 10-15 minutes in the same room with my rack, my head was not ok from the red/blue light. I change to white light and feel much much better. The plants are not complaining either!”
Plan for your electrical limitations
Another factor to keep in mind when designing your microgreen grow light setup is how much amperage your grow room electrical circuit can handle. My grow room is on a 15 amp breaker. You may find yourself with this same limitation. Planning out your lighting will keep you from the frustrations of tripping breakers and not being able to handle the lights you purchased.
Given the standard 80% breaker loading rule, a 15-amp circuit can handle about 1440 watts. A 20-amp breaker can handle 1920 watts. Here’s a quick reference of how many shelves you can light up with a single circuit:
Grow light watts-per-shelf
15 amp circuit
20 amp circuit
40 watts of lighting
36 shelves, 7.2 racks
48 shelves, 9.6 racks
42 watts of lighting
34 shelves, 6.8 racks
45 shelves, 9 racks
54 watts of lighting
26 shelves, 5.2 racks
35 shelves, 7 racks
60 watts of lighting
24 shelves, 4.8 racks
32 shelves, 6.4 racks
80 watts of lighting
18 shelves, 3.6 racks
24 shelves, 4.8 racks
This is a major reason you may want to use 40 watts per shelf, instead of 60 watts, 80 watts, or more. High-wattage lights can limit the amount of microgreen production your electrical circuit can handle.
If you are going to have 4 racks or more, you should plan your lighting to work within your electrical limitations. Especially if the circuit is shared with other home appliances, printers, lights, etc. It’s a real pain to start blending or printing only to trip the breaker and shut down the whole circuit.
If you have a small space limiting your microgreens production, this may not matter. If you’re just going to have a couple of racks in your kitchen, garage, or spare room, no worries about your breakers and light wattages. Light’em up!
Have even light-coverage of your microgreen trays
If you are using a 4-foot rack similar to the one we suggest, go with a 4 foot light. You’ll want to make sure the front and back have ample light, not just the center. One way to accomplish this is to use two lights instead of just one. Buying two 20-watt or 30-watt LED lights per shelf will work great. If you have a higher wattage light, you can use just one per shelf. Just make sure it’s far enough from the microgreens that the front and back of the trays also get sufficient light.
Get a quality grow light from a quality company
A quality light should have good reviews and warranty. These will help you know if the light is quality-made. If there are plenty of positive reviews, you should be safe. Also, check the warranty. It should be at least a one-year warranty.
Make sure to check out the company too. There are many foreign sellers online now, and it’s how to know if they will stick around or be able to handle any customer support issues.
My recommendation for the best microgreen grow light
I recommend 2 of Barrina’s 20-watt full-spectrum white grow lights per shelf. My space is tight, so I will never have more than 5 racks in this room. Even if I’m running a printer, my computer, monitor, fans, and other odds and ends, my circuit breaker should be fine.
To get the most out of the 40 watts, this light’s spectrum chart gives your microgreens the most benefit for the watts. The bulk of the energy is put into red. It does have a nice healthy blue to keep the microgreens from being too “stemmy”, some far-red to balance out the blue, and some green to increase growth efficiency and create a white light that allows me to properly monitor the health of the microgreens.
I’m also using mylar blankets on the front and back to focus the photons on the plants. Plus having two lights allows me to keep my lights about 6 inches from the plants to increase the light intensity that the plants are getting.
These lights have a 2-year warranty and a 4.7-star rating. They are from a well-known USA brand, not a here-today-gone-tomorrow China brand. They come in a 4-pack of 20 watts each for $60. This equates to $30 per shelf.
How much will it cost to light your microgreens?
Lighting cost will be a combination of the annualized cost of the lights and the cost of electricity to power them up.
- Annualized cost of the lights: LED grow lights typically last over 10 years, even running them 16 hours a day. So we divide their cost by 10 to get their annualized maintenance cost.
- Cost to power up the lights: The average cost of electricity in the United States is $13 per kWh. You will typically want your grow lights on for 16 hours per day. You can calculate your annual energy cost to light the shelf by multiplying watts x hours-per-year x cost of electricity per kWh, and then dividing by 1000.
For comparison’s sake, I’m noting here the grow lights that Donny Greens and Nate Dodson recommend. That way we can also judge the economics of these options.
Nate Dodson recommends two or three 20-watt shop lights per shelf. Since shop lights are not as effective as full-spectrum grow lights, we are going to calculate with three. This solution will cost you $49.53 annually.
Donny Greens recommends a 54-watt full-spectrum white grow light. This will cost you $49.38 per year.
Barrina 20-watt full-spectrum white grow lights will cost you $33.37 annually per shelf.
Annualized maintenance cost
Annual electricity cost
Total annual cost
SunBlaster 54w full spectrum
Barinna 3x20w shop lights
Barrina 2x20w full spectrum
None of these lights costs too much to disregard as an option. While the Barrina full-spectrum cost is slightly less, I wouldn’t base the decision of which light on the $16 a year savings. It’s too insignificant. But for all the other reasons mentioned in this article, I suggest going with Barrina’s 20-watt full-spectrum white grow lights.
If you would like to know the best growing medium for microgreens, check back, I will have it out soon!