The idea that plants need exposure to daylight for perfect growing conditions has persisted during the sustained growth of urban farming in the past half-decade.
But, as numerous researchers (and an increasingly large amount of growers) are starting to realize, the concept of sunlight as a necessity is, in fact, a flat out myth.
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.
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)
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.