The significance of light quality in cultivation

Oct 23, 2013 No Comments by

Contributed by: Niko Kivioja, CEO Netled Oy

Since there is a lot of discussion going on about using led lighting in plant cultivation from the point of view of energy savings compared to “old“ technology and that topic has been discussed on these forums quite thoroughly, I will now give a brief glimpse of the light quality point of view in the led lighting scene. The light quality itself is not a separate case from overall efficacy, because the ultimate efficacy is defined as produced revenue per kilowatt. In fact, the light quality plays even more significant role in the overall profitability of led lighting than technical efficacy itself. Incorrect light quality in cultivation setup may even prevent the wanted function from realizing, such as flowering of plants. This is the reason why some experiments have failed to promote LED lighting in a commercially feasible way. That’s why the quality of light should be in the center of discussion about the profitability of led lighting.

Plant under LED Lighting

Light quality is traditionally discussed as light spectrum and described by a curve over PAR defined region, which is from 400nm up to 700nm. Some enthusiasts demand to see this curve, but you can forget it. Although it is nice to look at and it represents a scientifically accurate expression of light quality, it cannot be evaluated for plant lighting without algorithms that actually evaluate its quantum yields. Furthermore, the definition of PAR radiation range ends at 700nm, while one of the key spectrum areas of interest is from 700nm to 800nm. This is why there is clear development in the plant lighting industry and research to

apply plant response based light quality definition method. I call it here as PRQR (Plant Response Quantum Ratio). This ratio is based on the idea that there are actually three wavelength regions in light that have distinguished effects on plant processes. By determining and calculating photon yields in these regions we have a way to classify different photons into three main groups. This way the complexity of PAR curves has been cut down to three different values. These spectrum regions are called as Blue, Red and Far red. In a nutshell; with this ratio, one can define the light quality according to its effect on the photosynthesis without going through the billions of variations of the whole PAR spectrum. When we add actual PPFD (photosynthetic photon flux density) to the quality definition, we have a method for describing plant efficient light with all the details needed to compare the light effectiveness in plant photosynthetic systems, but without expressing the awful amount of unnecessary information provided with actual spectrum curve.

So how can you evaluate the light quality using this PRQR? Well, first of all you need to evaluate what is the key function that you wish your crops to develop. Is it fruit production, biomass production or flowering? Some growers want to stretch the plants and some want to grow compact plants. Some want to induce flowering and some want to prevent flowering. With light quality a grower can manipulate these responses quite effectively. To give something to start with, red/far red is the key ratio in defining whether the light quality promotes or prevents flowering, while Blue affects e.g. anthocyanin development. These wavelength groups have quite wide range of determinable responses in plants. Increasing portions of certain wavelength group will promote the named function in plants. However, applying only single wavelength range won’t give you results, because plants and especially photosynthesis are very complex systems.

Accurate light ratios and further details on light color functions are usually the most protected knowledge of LED luminaire developers. This information has high potential for business advantage, whereas the LED luminaires themselves are technically fairly simple and do not possess a great potential for discovering new ground breaking properties. So the great future discovery most likely relies on dynamic controlling of light quality in relation to the plants´ growth cycle which is based on plant responses on certain light qualities. Giving growers this kind of tool set to control their production may lead to more stable food prices, better overall quality, more intriguing and stronger variety of flavors and in the end, increased food production capacity without increasing production areas. The future of led lighting is bright and most likely purple.

 

By

Niko Kivioja, CEO

Netled Oy

Niko is currently managing several LED lighting porjects in commercial greenhouses. Managing global partners in production. Technical development and evaluation.
With commercial growing background, Niko’s goal is to assist commercial greenhouses to increase their competive potential by offering innovative technological solutions for growth lighting.

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About the author

15 years horticulture experience to draw from
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