How Much Light Do Microgreens Really Need? Lighting Duration, Intensity, and Cost Considerations for Microgreen Growth

Lights I recommend – Barrina 4 Ft Grow Light, 8 Pack Amazon

When cultivating microgreens, providing the proper lighting is crucial for healthy growth and development. However, growers must balance several factors in determining the optimal lighting regimen. 

Key considerations include the duration and intensity of light exposure, as well as energy costs associated with the operation of grow lights. While microgreens require adequate light intensity and photoperiods to drive photosynthesis, excessive light can lead to heat and moisture stress. 

Growers must determine the sweet spot that provides sufficient light for vigorous growth without going overboard. The goals are to maximize growth rates and nutritional quality while minimizing costs.

Before You Dive into the Rabbit Hole Below (Laymens Terms)

While microgreens do need light for their growth cycle, they are still early in their development and almost any decent light source will work. My first lights were Hypertough shop lights that I bought from Walmart for 16$ each. 

The next set I bought was a cheap set of 4 2ft grow lights from Amazon and finally I have started purchasing these 4 Ft Barrina grow lights from Amazon that come out to around 12 dollars each. 

The interesting part is that while I tested the light densities to see if they were near the numbers discussed below, I did not see much difference in how plants grew under them. 

I believe this is largely because plants need different light spectrums during certain points in their growth cycle, Microgreens are harvested before this becomes an issue and any light provides that initial boost that they need. 

Determining the Minimum Light Intensity Thresholds for Microgreen Growth

When setting up a lighting system for microgreens, one of the first questions is how much light is actually needed. Research studies have aimed to determine the minimum light intensity thresholds for optimal microgreen growth. 

One study tested a range of light intensities from 50 to 200 μmol/m2/s using red and blue LEDs. They found that cotyledon and hypocotyl growth increased proportionally with light intensity up to 150 μmol/m2/s, with little additional benefit beyond this level. Other studies have recommended minimum intensities of 100-120 μmol/m2/s for microgreens, with ideal ranges of 120-200 μmol/m2/s. 

Growers should provide at least 100 μmol/m2/s at the plant canopy level, while intensities above 200 μmol/m2/s may be excessive depending on other factors.

If you wish to test this number for yourself, you can download the app Photone. This app allows you to measure light levels using the camera of your phone and can be tailored to the specific light type that you are using. 

LED vs Fluorescent – Comparing Lighting Types by Intensity and Costs

When selecting between LED and fluorescent grow lights, factors like upfront costs, longevity, and light intensity come into play. LED lights have become popular for microgreens thanks to higher light intensity per watt compared to fluorescents. 

High-output LEDs can supply over 200 μmol/m2/s for optimal microgreen development. While LED fixtures are more expensive initially, electricity costs are lower and bulb lifespan is up to 50,000 hours compared to 20,000 hours for fluorescents. Fluorescents require almost double the wattage of LEDs to achieve the same intensity. 

While fluorescent tubes must be replaced frequently, LEDs provide consistent intensities over years of operation. The longer lifespan and lower electricity use make LEDs more economical in the long run.

Growers intending to enter the commercial market should evaluate costs over a 5-10-year period when choosing between LED or fluorescent fixtures.

Balancing Lighting Costs and Growth Rates

Microgreens growers must strike a balance between the significant costs of indoor lighting and the benefits of faster, high-quality growth. 

Economical options like T5 fluorescents or older LED models can supply adequate intensity for microgreens at lower equipment prices. Run times can be kept short to provide enough light for growth while limiting energy use. However, tighter spacing of plants may be required. 

Upgrading to more powerful lights can accelerate growth rates by 25-50% compared to low-intensity lighting. But operating costs will also increase, so growers should determine if the extra production outweighs the electricity bill. 

Timers and controllers allow precise photoperiod management to avoid excessive lighting. Growers can experiment with different light levels, durations, and plant densities to find the balance between growth, quality, and affordability.

How Many Hours of Light

While you may think it makes since to give plants as much light as possible since they need light to grow, keeping your lights on 23 hours a day would actually harm your plants.

Most plants tend to store the energy from the light while exposed to it, then use that energy to grow while they do not have light available.

With that in mind, a duration of 12 to 16 hours is ideal for most plants.

Managing Heat and Moisture Stress from Intense Lighting

One downside to high-intensity discharge or LED grow lights is the heat load. Dense microgreens under hot grow lights can experience wilting, tip burn, and other issues related to moisture stress and excessive transpiration. 

Light intensities over 500 μmol/m2/s require careful climate control to avoid rapidly drying the plant and root zone. Increased ventilation, fans, dehumidifiers, and AC may be necessary to cool and dry the air to offset intense lighting.

Lower density spacing can also help reduce moisture stress. Growers using less intense fluorescents or LEDs are less likely to encounter these issues. 

But when pushing for maximum growth rates, the heat of high-power lights must be managed through environmental controls to prevent damage to delicate microgreens.

Conclusion

Optimizing lighting for microgreens involves finding the right balance between growth rates, product quality, and affordability. While intense light promotes rapid growth, costs can become prohibitive and heat management challenging. 

Research indicates minimum intensities around 100 μmol/m2/s are needed, with ideal ranges between 120-200 μmol/m2/s. LEDs provide high-intensity output at lower electricity costs than fluorescents over the long term. 

Growers should experiment with different lighting durations, intensities, and space configurations to find the sweet spot for their particular setup, production goals, and budget. With a good understanding of light quantity requirements and management of heat/moisture stress, microgreen producers can maximize quality and yields in an efficient, cost-effective manner.