In the last white paper, the concept of dynamic lighting was introduced and four key criteria that a truly dynamic solution needs to meet were identified:
With these criteria in mind, some of the benefits of dynamic lighting were described – one of which was improved energy efficiency. In this white paper, the topic of energy efficiency will be discussed in greater detail by considering how a truly dynamic lighting solution can apply spectral compensation, in addition to intensity regulation, to preserve energy in a greenhouse.
Spectral compensation is only made possible using truly dynamic variable spectrum lighting systems such as Sollum Technologies’ smart LED solution. In the same way that dynamic lights can modulate their output intensity based on changes in ambient light, they can modulate their output spectra based on the ambient spectrum. The spectral makeup of sunlight varies based on weather and climate and the spectral needs of plants vary based on crop and growth stage. When spectral compensation is not available, growers can only attempt to accommodate the light quality needs of their crops by adjusting the intensity of their fixed spectrum supplemental lights.
For instance, if crops are lacking in one wavelength band but spectral compensation is not available, the overall intensity of the light will have to be raised, which increases the availability of all wavelengths in the light’s spectrum. From an energy standpoint, meeting a crop’s lighting needs using intensity control alone is inefficient because making a light brighter to fill gaps in spectra consumes unnecessary additional electricity. It also fails to consider how wavelength ratios impact plant photoreceptors and resulting growth patterns of response (Seguin, 2022). Using spectral compensation, wavelengths can be targeted specifically by adjusting a light’s spectral output in real time without an unnecessary increase elsewhere in the spectrum.
A result of employing spectral compensation in combination with intensity modulation is that the total DLI of a crop can be reduced during periods of peak electrical grid demand without interrupting the productivity of the crop. If precision lighting systems that offered dynamic compensation were adopted by all greenhouses, pressure from the sector on utility providers could be greatly reduced and barriers to new projects and expansions could be removed.
In the following sections, the concept of spectral compensation in conjunction with intensity modulation will be elaborated upon using detailed examples.
Total dynamic real-time sunlight compensation can only beachieved using advanced variable spectrum capable lighting.
An earlier white paper titled “Seasonal Variation in Natural Light” discusses in detail how sunlight changes both seasonally and daily in terms of both intensity and spectra. To recap, the major factors that contribute for variation in natural light over the course of a day or a year are solar elevation angle – i.e., how high the sun is in the sky and the resulting angle of incident sunlight on the Earth’s surface – and atmospheric composition which results in differential scattering of light by particles in the atmosphere (Seguin, 2022). Without spectral compensation, a smart lighting solution’s only manner of response to a cloudy day, for instance, would be to increase lighting intensity – thus consuming more electricity overall. However, the relationship between weather and natural light is complex and cannot be addressed by considering brightness alone.
Researchers Chiang et al., (2019) conducted an in-depth study that tracked all the spectral changes of natural light at a mid-latitudinal location over the course of an entire year. Their findings highlight the significant impacts of atmospheric weather events on the natural light available to plants and how weather and climate factors interact to further complicate light patterns. In a general sense, from sunrise to sunset, the researchers observed that blue light (400 – 500 nm) will decrease as the day progresses and green (500 – 600 nm), red (600 – 700 nm) and far-red (700 – 780 nm) wavelengths will increase (figure 1.)
They found that the solar elevation angle and weather events together had compounding effects. For instance, at low solar elevation angles – i.e., during sunrise or sunset – the red to far-red light ratio maybe 0.8 on a cloudy day and 1.3 during clear sky conditions. At solar elevation angles lower than 20°, atmospheric weather conditions will strongly impact available red and blue wavelengths in the light spectra such that a significantly higher proportion of red light and a lower proportion of blue light will result. During mid-day – at higher solar elevation angles – the opposite trend was observed but to a lesser degree with the proportion of blue light increasing marginally with increasing cloud cover, and the proportion of red light decreasing marginally.
A truly dynamic lighting solution – like that of Sollum Technologies’ – can address weather variation by adjusting light spectra as well as light intensity in immediate response to changes in ambient light. For other smart lighting systems, mimicking clear sky conditions on a cloudy day can only be attempted by increasing brightness – thus consuming additional electricity that may not be necessary. Precise sunlight compensation fine-tuning both the spectrum and intensity leads to energy savings.
The following graphic provides an example of dynamic compensation as accomplished by one of Sollum Technologies’ smart LED grow light. In this example, the following light recipe is precisely and accurately maintained thanks to dynamic compensation: LED lights turn on early in the morning – before sunrise – and recreate the full sunlight spectrum including far-red (the grower may choose to include far-red for several reasons such as to promote shoot elongation during vegetative growth in crops). As the Sun rises, not only is more photosynthetically active radiation (PAR) available to the plants, but more far-red light is available as well, and the ratio of blue to red light decreases. Responding in real time, the intensity of the LED lights is reduced, far-red is deactivated and the fixture’s blue:red wavelength ratio output is increased. As the Sun sets, the intensity of the LEDs rises, the spectrum shifts accordingly and far-red is reactivated. This is only one possible light recipe out of an infinite number that may be employed using Sollum Technologies’ smart LED grow light solution.
Precise sunlight compensation fine-tuning both the spectrumand intensity components leads to energy savings.
In addition to addressing variation in terms of weather and climate, dynamic lighting and spectral compensation can also be used to accommodate varying needs of plants during different growth stages. Fine tuning artificial lights to precisely provide what a plant needs, when it needs it, will improve overall efficiency – i.e., the kWh/kg ratio. The more optimized a greenhouse facility is for the growth of the harvested crop, the less energy input is needed relative to the biomass of the crop yield.
Put another way, optimized greenhouse operations can output higher quality yields for the same amount of energy consumed by a less efficient facility. Specific lighting treatments can be used to trigger metabolic responses that improve plant anatomy, chemical composition, physiology, growth and reproduction – effectively providing a grower “more bang for their buck” energy-wise.
Even in the earliest stages of plant growth, differential application of spectra and intensity can result in significant overall energy and economic savings (Chang et al., 2014: Poulet et al., 2014). Poulet et al. (2014) found that the energy conversion rates of lettuce (the rate at which lettuce plants convert light energy to biomass), grown under LED lighting vary depending on growth stage. During the lag phase of growth (the first 10-15 days past germination) they found that 0.35 g of biomass per kWh of light was produced; this ratio increased to 2.78 g/kWh during the exponential phase of growth (when growth is fastest). The difference in the amounts of electricity consumed by the growing operations during these phases (17 kWh during the lag phase versus 26.8 kWh during the exponential phase was much less pronounced (1:1.6 compared to 1:8). In other words, a significant amount of supplemental light did contribute to crop biomass during the lag phase of growth. Given their findings, these researchers emphasized that there is much room for lighting optimization during the early stages of plant growth to achieve significant energy savings.
For other crops – such as cucumbers and tomatoes – there are distinct vegetative and fruiting stages of growth before harvest that also benefit from differential light treatments. Blue light promotes vegetative growth – the development of shoots and leaves – while red light promotes the development of flowers and fruit (Xu et al., 2016). As discussed in the previous section, the ratio of red to blue wavelengths available in natural light can change depending on environmental factors. A dynamic lighting solution can account for changes in ambient light due to environmental factors in order to maintain a specific lighting recipe that considers the growth stages of a crop; this way, energy is conserved when wavelengths for a crop’s distinct growth stage are sufficiently present in ambient light.
Finally, a dynamic lighting solution can also improve energy efficiency simply by improving the growth rate of crops. Chang et al., (2014) showed that when the output spectrum and intensity of supplementary lighting was precisely managed and purposefully regulated to meet plant needs, the growing period of lettuce could be significantly reduced, thus resulting in energy savings.
Specific lighting treatments can be used to trigger metabolic
responses improving plant anatomy, chemical composition,
physiology, growth, and reproduction.
Albright, L., Both, A. J., Chiu, A. (2000). Controlling greenhouse light to a consistent daily integral. Transactions of the ASAE, 43, 421–431. https://doi.org/10.13031/2013.2721
Chang, C.-L., Hong, G.-F., Li, Y.-L. (2014). A supplementary lighting and regulatory scheme using a multi- wavelength light emitting diode module for greenhouse application. Lighting Research & Technology, 46(5), 548–566. https://doi.org/10.1177/1477153513495403
Chiang, C., Olsen, J. E., Basler, D., Bånkestad, D., Hoch, G. (2019). Latitude and Weather Influences on Sun Light Quality and the Relationship to Tree Growth. Forests, 10(8), 610. https://doi.org/10.3390/f10080610
Hydro Quebec. (n.d.). Additional Electricity Option for Photosynthetic Lighting or Space Heating to Raise Crops. Retrieved March 27, 2022, from https://www.hydroquebec.com/residential/customer-space/rates/additional-electricity-option-crops.html
Elkins, C., Iersel, M. W. van. (2020). Longer Photoperiods with the Same Daily Light Integral Improve Growth of Rudbeckia Seedlings in a Greenhouse. HortScience,55(10),1676–1682. https://doi.org/10.21273/HORTSCI15200–20
Katzin, D., Marcelis, L. F. M., van Mourik, S. (2021). Energy savings in greenhouses by transition from high- pressure sodium to LED lighting. Applied Energy, 281, 116019. https://doi.org/10.1016/j.apenergy.2020.116019
Kotilainen, T., Aphalo, PJ., Brelsford, CC., Böök, H., Devraj, S., Heikkilä, A., … Robson, TM. (2020). Patterns in the spectral composition of sunlight and biologically meaningful spectral photon ratios as affected by atmospheric factors. Agricultural and Forest Meteorology, 291, 108041. https://doi.org/10.1016/j.agrformet.2020.108041
Posterity Group. (2019). Report of Findings: Greenhouse Energy Profile Study (p. 170). Ottawa, Ontario: Independent Electricity System Operator. Retrieved from https://www.ieso.ca/-/media/Files/IESO/Document-Library/research/Greenhouse-Energy-Profile-Study.ashx
Albright, L., Both, A. J., Chiu, A. (2000). Controlling greenhouse light to a consistent daily integral. Transactions of the ASAE, 43, 421–431. https://doi.org/10.13031/2013.2721
Chang, C.-L., Hong, G.-F., Li, Y.-L. (2014). A supplementary lighting and regulatory scheme using a multi- wavelength light emitting diode module for greenhouse application. Lighting Research & Technology, 46(5), 548–566. https://doi.org/10.1177/1477153513495403
Chiang, C., Olsen, J. E., Basler, D., Bånkestad, D., Hoch, G. (2019). Latitude and Weather Influences on Sun Light Quality and the Relationship to Tree Growth. Forests, 10(8), 610. https://doi.org/10.3390/f10080610
Hydro Quebec. (n.d.). Additional Electricity Option for Photosynthetic Lighting or Space Heating to Raise Crops. Retrieved March 27, 2022, from https://www.hydroquebec.com/residential/customer-space/rates/additional-electricity-option-crops.html
Elkins, C., Iersel, M. W. van. (2020). Longer Photoperiods with the Same Daily Light Integral Improve Growth of Rudbeckia Seedlings in a Greenhouse. HortScience,55(10),1676–1682. https://doi.org/10.21273/HORTSCI15200–20
Katzin, D., Marcelis, L. F. M., van Mourik, S. (2021). Energy savings in greenhouses by transition from high- pressure sodium to LED lighting. Applied Energy, 281, 116019. https://doi.org/10.1016/j.apenergy.2020.116019
Kotilainen, T., Aphalo, PJ., Brelsford, CC., Böök, H., Devraj, S., Heikkilä, A., … Robson, TM. (2020). Patterns in the spectral composition of sunlight and biologically meaningful spectral photon ratios as affected by atmospheric factors. Agricultural and Forest Meteorology, 291, 108041. https://doi.org/10.1016/j.agrformet.2020.108041
Posterity Group. (2019). Report of Findings: Greenhouse Energy Profile Study (p. 170). Ottawa, Ontario: Independent Electricity System Operator. Retrieved from https://www.ieso.ca/-/media/Files/IESO/Document-Library/research/Greenhouse-Energy-Profile-Study.ashx