The term “dynamic lighting” is becoming more common in the world of precision agriculture. The concept of dynamically controlling artificial light is in its infancy, and as such the definition of exactly what constitutes “dynamic lighting” is not always consistent between sources. Sollum Technologies identifies four fundamental criteria for its lighting technology to be truly dynamic:
In this paper, we will break down these criteria and discuss the invaluable agricultural advantages that they present.
Being able to change a light’s output intensity means altering a fixture’s light both quantitatively and qualitatively. Out of the most common grow light options, LEDs provide significantly more freedom when it comes to managing output. Altering light intensity is most referred to as “dimming”, which provides the ability to reduce intensity down from full power levels.
Dimming is a desirable feature in a greenhouse because it allows the producer to save energy during periods where more solar radiation is available. Experts, however, often advise against dimming when it comes to high pressure sodium (HPS) or metal halide lights because it can limit the available light spectrum (Figure 1).
Alternatively, the output spectra of LED lights is relatively unchanged by dimming mechanisms (Elkins and Iersel, 2020). The reason for the discrepancy between the impacts of dimming HPS and HID lights versus LED has to do with temperature and with the dimming mechanism. With HID and HPS, light and heat production are intrinsically linked such that reducing the temperature of the lights will change the output spectrum – this means that reducing the power to the light fixture to dim the lights also reduces the heat production, which alters the spectrum. LEDs are the most energy efficient light fixtures – converting 47% of input power to light. Alternatively, HPS converts just 34% of input power to light and the rest of the energy is lost to heat. Thanks to the reduced heat production of LEDs, their light spectrum is primarily unchanged even when they are not operating at full power – i.e., are dimmed.
Compared to alternatives, LEDs allow enormous freedom in terms of spectral output with a variety of narrow and broad-spectrum fixtures available. The flexibility of a LED fixture’s output spectrum is due to the nature of diodes – each diode on a fixture can emit a different single wavelength, and with the help of a phosphor coating some diodes can emit a mixture of wavelengths to produce white light. Because LEDs are energy efficient and their cooling load is minimal, many diodes of varying outputs can be included on the same fixture – making broad and full spectrum options available. The output spectrum of HPS and metal halide fixtures is fixed and can only be changed using filters, or as mentioned previously, by changing the temperature of the light – making a dynamic change in the output spectrum unfeasible for these types of light.
Despite the perceived flexibility that LEDs offer, most LED options on the market deliver limited benefits to growers. While LEDs enable the manufacturer to create different light spectrum, the grower has to select a specific one and once delivered, that fixed spectrum cannot be changed. Narrow spectrum LED fixtures are a popular choice that offer growers a mixture of red and blue light – the two wavelengths that are most efficient for plant photosynthesis. However, these lights lack green, yellow, UV and far-red light which can offer plants a variety of other benefits related to plant morphology, disease resistance, photosynthesis, etc. (Johkan et al., 2012; Meyer et al., 2021; Tan et al., 2021). Broad spectrum lights are also available so that plants have access to wavelengths other than red and blue, but the energy efficiency is reduced by the phosphorous coating used on diodes to create a broad-spectrum output.
When acquiring a dynamic lighting solution, the grower shall have a system that can both managed in intensity and spectrum output.
Sollum Technologies is the only LED grow lights provider that offers a truly dynamic output enabling the optimal combination of broad- and narrow-spectrum light recipes that can be used to perfectly recreate sunlight, precisely apply far-red light to control morphology, emphasize red and blue for rapid periods of growth and allow growers the freedom to change their lighting strategy as research evolves.
It is one thing to have the ability to change the output of a lighting system, but it is another to always have complete remote control and monitoring capabilities of the lighting system at all times. For most grow lights, programming capabilities are as basic as using a timer to turn lights “on” and “off” for photoperiod management. A truly dynamic lighting solution is one that allows growers to input commands and light recipes – such as programming lights to transition smoothly from a sunrise spectrum to a sunset spectrum.
The controlled application of different spectrums is what is meant by light recipe. When baking a cake, it is not enough to have a list of ingredients – a recipe must include instructions on when to incorporate the ingredients and in what quantities; a light recipe accomplishes the same thing: it is a program that controls the application timing and intensity of different spectra.
With Sollum’s dynamic lighting solution, growers can implement an unlimited number of recipes and have access to expert consultation on recipe choice informed by the most recent research.
Another novel advancement that truly dynamic lights offer is the ability to program fixtures collectively and spatially. Instead of programming one light at a time, an entire greenhouse lighting layout can be managed. Sollum’s dynamic solution allows greenhouse lighting to be programmed by zone (Figure 2), providing a number of benefits: for instance, a light recipe can follow seedlings as they are transported from a misting room to a different location equipped with driplines, or a greenhouse space can be easily adapted to introduce a new crop native to a different geographical region.
While other lighting providers may offer custom lighting to growers, they do not allow these lights to be re-programmed in the future. A truly dynamic solution adapts to a grower’s strategy as it changes over time with evolving research and consumer demand. Sollum’s smart LED lighting solution allows users to execute an infinite number of light recipes that can be changed and scheduled over time.
During the discussion of programmability, time and space were identified as variables, i.e., programming light to change according to the time of day and according to zones in a growing space. Truly dynamic lighting solutions, however, are also responsive to environmental cues – specifically, ambient light. In many grow light applications, natural sunlight is available in some quantity during some period of the day. The ability of a grow lights system to sense sunlight the quantity and quality of sunlight levels, and modulate output accordingly, gives growers complete control over the light environment in their growing space and leads to optimal energy efficiency.
As previously mentioned, the ability to dim grow lights is a desirable feature because it allows growers to reduce the overall energy consumption of their lights. Sensing ambient light levels, and dimming accordingly, seems like a sensible characteristic to include in the design of a fixture. Despite this, responsive dimming has received relatively little attention in the controlled environment and greenhouse industries and consumers still have few choices of grow lights that include such a feature.
For LEDs, there are two mechanisms available for dimming: current reduction and pulse width modulation. Current reduction involves reducing the electrical current to the fixtures, which continuously reduces the output intensity. Pulse width modulation (PWM) involves turning the lights on and off at high frequencies and controlling the ratios of the on/off cycle, which gives the appearance of dimming (Iersel and Gianino, 2017). In 2017, researchers Iersel and Gianino tested the energy saving potential of an adaptive dimming system. They compared three treatments: 1. LED lights at full power for a 14-hour photoperiod; 2. LED lights turned on only when the photosynthetic photon flux (PPF) available from ambient light dropped below a certain threshold; and 3. LED lights dimmed using PWM to maintain overall light levels at the specified PPF threshold. These researchers found that, while some crops responded differently to varying PPF thresholds, using the adaptive PWM method reduced electricity use significantly (from 20% to 90% depending on the PPF threshold) and efficiently maintained desirable light levels for crop growth).
While options on the market are limited for lighting solutions with dimming capabilities, they are almost non-existent for systems that react to changes in light spectra. The technology involved in sensing and modulating the spectral output of LED lights accurately is much more complicated than adjusting intensity – and so it is responsiveness with regards to spectra that often separates a smart lighting solution from a truly dynamic one. Sollum Technologies’ smart LED light fixtures are capable of spectrum compensation, which means that light recipes will adapt to the spectral composition of ambient light as it changes over time.
The figure below illustrates how, as discussed in previous white papers, the Sun’s natural output changes in response to the period of the day and atmospheric conditions. If a producer wishes to replicate clear sky conditions for their geographic region, or another,
Sollum’s fully dynamic lighting solution could complement naturally available sunlight by filling gaps in the spectrum – thus providing a more efficient lighting solution than one that consistently outputs full spectrum light.
Iersel, M. W. van, Gianino, D. (2017). An Adaptive Control Approach for Light-emitting Diode Lights Can Reduce the Energy Costs of Supplemental Lighting in Greenhouses. HortScience, 52(1), 72–77. https://doi.org/10.21273/HORTSCI11385-16
Johkan, M., Shoji, K., Goto, F., Hahida, S., Yoshihara, T. (2012). Effect of green light wavelength and intensity on photomorphogenesis and photosynthesis in Lactuca sativa. Environmental and Experimental Botany, 75,128–133. https://doi.org/10.1016/j.envexpbot.2011.08.010
Iersel, M. W. van, Gianino, D. (2017). An Adaptive Control Approach for Light-emitting Diode Lights Can Reduce the Energy Costs of Supplemental Lighting in Greenhouses. HortScience, 52(1), 72–77. https://doi.org/10.21273/HORTSCI11385-16
Johkan, M., Shoji, K., Goto, F., Hahida, S., Yoshihara, T. (2012). Effect of green light wavelength and intensity on photomorphogenesis and photosynthesis in Lactuca sativa. Environmental and Experimental Botany, 75,128–133. https://doi.org/10.1016/j.envexpbot.2011.08.010