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Is white light better for plants?


Recent publications have suggested that supplementing broad spectrum (white) light to plants is preferred above supplementing narrow banded (purple) light. In those publications the use of white light is also linked to working conditions. In this article we want to explain the choice for certain light spectra and their effect on plants and people.

 

At Signify we conduct in-depth research to understand how individual crops respond to different light spectra, because recommending the right LED spectrum for each situation is an essential element in our offer. The spectra of our lighting products are developed for optimal growth and development of crops at the highest energy efficiency.

 

Plants use light as a source of energy to drive their photosynthesis (growing) and as a source of information to trigger photoreceptors that drive plant development (signaling). Both processes take place simultaneously and interact with each other. Let’s look a bit deeper to the effect of supplemental light on these two elements.

 

Supplemental light

The primary growth process for plants is photosynthesis. All colors within the photosynthetically active radiation range (400-700nm) contribute to photosynthesis (see fig 1). However, red light is the most energy efficient growth light for plants for several reasons:

  • Red photons are (along with blue) the most efficiently absorbed by plants
  • Within the leaf, red photons are most efficiently used in photosynthesis
  • Red LEDs give most photons per watt of electricity

These three factors explain why red LEDs are a key ingredient in many of our lighting solutions.

 

But, there is more to a good spectrum than just photosynthesis. Many processes in plants such as stomatal opening, rooting, flowering and stretching are triggered by different parts of the spectrum. This is called signaling. Research has shown that, amongst others, Blue and Far Red trigger the signaling processes.

 

Signify has conducted extensive research to find the optimal spectrum for many crops. Our research has clearly demonstrated that the spectral needs are different per crop and per growing objective. This is the reason we have a portfolio of products with different spectra.

 

By combining the right colors needed for optimal growth, our lighting solution is tailored to deliver the desired yield and quality attributes per crop AND is more energy-efficient compared to ‘broad spectrum (white) lamps’.

 

Working conditions

Greenhouses and vertical farms are environments which are optimized for the growth of crops, but of course need to be safe and comfortable working environments for people as well. Needless to say, all our lamps meet the necessary safety standards, including photobiological safety standards.

 

Regarding eye comfort: the human eye is most sensitive for yellow/green light, but also has a great capability to adapt to different lighting environments. This means that it is not necessary to have high color rendering to perform tasks in a greenhouse. In greenhouses there is usually ample daylight during working hours, which allows for good visual quality, irrespective of the spectrum of the supplemental lighting. In a vertical farm, the crop growing area and plant inspection area can be illuminated with a different light spectrum.

 

For our customers who prefer more human eye comfort, we have spectra which include ‘White’ LEDs that provide sufficient white light to comfortably perform most labor tasks, such as harvest and scouting even in the absence of daylight. Interesting point: the HPS lamps, which are currently by far the most used light sources in greenhouses, have a very poor color rendering, but still they are well accepted for this working environment.

 

So, is white light better for plants?

Concluding, we can say that in general narrow banded light is the most energy efficient way to grow high quality crops. The exact light spectrum differs per crop. Adding white light to this environment improves eye comfort for people.

Signify offers both options in its portfolio to make sure the grower can make his preferred choice fitting his objective.

Figure 1. McCree curve showing photosynthesis efficiency as a function of wavelength

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