Growing Microgreens Indoors: The Advanced Guide (2020 Edition)

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- Zjef Van Acker, Former Chief Engagement Officer, Association for Vertical Farming (AVF) 

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Why LED lighting is ideal for indoor farming

According to data from National Geographic, the sun radiates enough energy in 15 minutes to equal energy consumption of the entire world for ONE YEAR.

The sun is so powerful that it was worshiped by ancient cultures.

So how is it possible to have lighting for growing plants indoor that is actually more efficient than the sun?

And why is it often a shade of purple???

Why is LED lighting is ideal for indoor growing?

Ancient cultures worshiped the sun due to its life giving power (source)

The idea that plants need exposure to daylight for perfect growing conditions has persisted during the sustained growth of indoor farming in the past several decades.

But, as numerous researchers (and an increasingly large amount of growers) have realized, the concept of sunlight as a necessity is, in fact, a flat out myth.


Read on to find the step-by-step explanation for how LED lighting is revolutionizing indoor growing, and more!

Why purple LED lighting is ideal for urban farming

In the rest of the article we will discuss:

1) Why Purple (a.k.a. blue-red LEDs?
2) LED Lighting vs Daylight
3) PROS and CONS of LED Grow Lights


Let's get started!

Why Purple (a.k.a. blue-red) LEDs?

The technical answer, in a nutshell, is related to the spectrum of color present in different types of light. While good 'ol sunlight contains a variety of color spectra (think rainbows), it turns out that plants only need specific color spectra to grow properly.

What colors work best?

According to urban farming research on the way plants respond to light, the blue-red spectra is ideal for plant growth.

The reason for this is because chlorophyll, which plays a central role in plant growth and photosynthesis, responds primarily to "peak" spectra in the blue and red ranges, or 450 nanometer and 650 nanometer wave lengths respectively.

Some research has also experimented with using other forms  of light in urban agriculture growing settings, often yellow LED spectra, to alter plant traits such as color, texture, and increased shelf life.

With a consumer base increasingly enamored by rare and interesting varieties of common fruits and vegetables, concepts such as red or yellow carrots can be marked up as exotic items or at the very least add some extra zest for small-scale urban farmer.

Plant growth does not require the full spectra present in daylight

Plant growth does not require the full spectra present in daylight (via Illumitex)

LED Lighting vs Daylight

Sunlight, in fact, is inefficient in many ways when it comes to optimizing small-scale, urban agriculture.

For one, the heat generated by the sun can be damaging to plants and can have an adverse effect on shelf life immediately post harvest.

This "heat effect" caused by sunlight is even further amplified when the plants are closely packed, as is often the case in urban farming.

In contrast to sunlight, LED lights are known for transferring nearly undetectable amounts of heat onto plants, and the bulbs themselves are even often cool to the touch. The result?

Urban farms with LED lighting can have more closely packed arrangements for maximum efficiency. These arrangements would not be possible in normal agricultural environments without compromising the health of the plants.

Besides the decreased heat transfer, LED lighting is a cheaper alternative to traditional lighting sources that emulate daylight conditions.

Although there is often a higher upfront cost with LED lighting, the best way to view the cost-savings of LED lighting for urban farming is as a long-term investment.

This is because LED lighting has a much higher energy efficiency over time compared to other urban farming lighting technologies such as halogen or compact fluorescent (CFL).

As a quantitative example, average CFL lighting options on the market will have approximately 1/3 the lifespan of LED lighting options, with similar lighting strengths (Look for 12-16 W / 800-1000 Lumens)

Plants, due to the presence of chlorophyll necessary for photosynthesis, respond mainly to red&blue

Plants, due to the presence of chlorophyll necessary for photosynthesis, respond mainly to red and blue color spectra (via NPR)

Pros and Cons of LED Grow Lights


1) LED's use WAY less electricity:

Most LED grow lights use 40% - 50% of the wattage of other lighting sources, like high pressure sodium lights or fluorescent.

2) Less airflow needed

It is a simple fact that for indoor growing, proper ventilation is required.

According to this post from Epic Gardening, ventilation for indoor growing helps prevent at least:

  • Excess Moisture
  • Proliferation of Pests
  • Weakening of Plant Stems

Now, can you guess the #1 cause of heat in an indoor growing environment?

That's right: Grow lights.

But here's the catch:

LEDs generate far less heat than all other types of grow lights. As a result, less ventilation is needed to prevent excess moisture, pest problems, and other ventilation related issues.

From an economic perspective, smaller fans cost less than larger fans, so your ventilation investment requirement with LED grow lights will typically be lower than with other types of grow lights.

Additionally, the on-going electricity cost of powering fans is also eliminated.

3) Less Heat

As we have already discussed above (#2), LEDs generate far less heat than other grow lights.

Now, the reason why LED's generate less heat is because they emit far less infrared heat as output.

Other types of grow lights like high pressure sodium and metal halide grow lights emit enormous amounts of infrared heat - over half of the wattage that powers an HPS or MH light is instantly lost as heat.

Bottom line?

LEDs are far more efficient and produce far less heat.

4) EXTREMELY long life

LED's grow lights are as close to immortal as grow lights get:

They typically have at least 50,000 hours of usable life, which is nearly 6 years of continuous use.

If you are utilizing the lights on a 50% on /50% off schedule (common benchmark), this is over 11 years of shelf life.

5) No need to purchase reflector equipment to improve efficiency

HPS/MH systems often require use reflectors to help re-capture light that was not directed toward plants and instead illuminates walls and ceiling.

LED's have superb directional focus and therefore reflectors are not necessary.

6) Stackability

Because LED's have so much lower heat emission, they can be placed closer to the plants.

The result of this is that the ability to "stack" plants in a growing space is possible.

This is potentially the most exciting benefit of using LEDs: the potential to double the production output (or triple, or 4x, etc) without changing the area of the growing space.

Now, one consideration to remember is that the height of the growing space is a factor.

However, this type of stacking functionality is just not doable with other types of grow lights.


1) Upfront Cost

LED's will commonly be at least 2x more expensive then many other types of grow lights.

The return on investment may pay off over time with less energy use, replacement cost, and less investment in other previously needed equipment like fans and reflectors.

See how the economics compare with the case study from Diffen above.

2) Heavy

The component of an LED grow light that makes it heavy is the heat sink, which helps absorb excess generated heat.

As a rule of thumb, a quality LED grow light will have 10 square inches of heat sink space per LED watt.

If you do the math, you will see that this heat sink space adds up VERY quickly and adds a lot of weight.

The result of this is that investment to support the weight of LED grow lights is often a good idea, *especially* if you are stacking layers into a vertical farming style system.

3) Technology Still Developing

As far as commercial indoor growing, LED technologies have not been around for very long (less than 10 years).

Previously lighting methods have included High Pressure Sodium and Metal Halide lighting.

One risk with LED lights is that they are understood less thoroughly than other types of grow lights, which have been studied for several decades.

What does this mean?

Essentially, the support and knowledge base for LED grow lights is far more limited than other types of grow lights.

However, where there is a knowledge gap, there is also opportunity...

4) "Purple" Color

The purplish color that most LED grow lights will generate can be problematic beyond just being annoying:


This color of lighting presents a couple real challenges that can become huge problems:

  • Pest damage is harder to identify with LED grow lights
  • Nutritional deficiencies, such as yellow under-nourishment and black rot, are more difficult to identify
  • Potential danger to YOUR eyes without proper protection. As detailed in this article from Electronics Weekly, the potential to damage your vision with LED lights is very real, and protective eyeware is best practice

Solution: Inspecting plants being grown with LED grow lights is best done using an alternate source of light, such as a fluorescent bar. Most commercial LED operations will inspect plants with fluorescent lights at least once every 10 days.

In Summary

So, why does all of this information matter? In an urban farming environment where space and resources may be limited, optimizing lighting will often be a winning strategy for best urban farming results.

- Red and Blue light (purple when combined) are optimal for plant growth in tightly packed, urban farming style conditions

- LED lighting has several advantages over daylight or other lighting alternatives, such as cheaper pricing over time and reduced heat transferred onto plants

- Experimentation with other color spectra with LEDs such as Yellow LEDs can cause changes in urban farming crop flavor, color, and other aesthetic characteristics.

- There are many pros and cons to using LED grow lights. In general, LEDs are far more efficient than other types of grow lights in many aspects, however they are more expensive and still relatively new as far as large scale commercial use goes.

Questions, comments, feedback? Follow us @urbanvineco

“If had existed when I got into Vertical Farming back in 2012, I'd have saved 3 years in that quest to learn it!”

- Zjef Van Acker, Former Chief Engagement Officer, Association for Vertical Farming (AVF) 

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