Introduction to Dynamic Lighting

By Sollum’s R&D Team
February 22, 2024

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:

  1. Output intensity that can be changed effortlessly;
  2. Light spectrum   that   can   be   modified   and   tailored endlessly;
  3. Programmable and reprogrammable lighting scenarios;
  4. Responsiveness to ambient light.

In this paper, we will break down these criteria and discuss the invaluable agricultural advantages that they present.

Output intensity that can be changed effortlessly

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).

Figure 1: Spectral changes for HPS and metal halide fixtures dimmed to 75% and 50% intensity. Source: “To Dim or Not to Dim Your Grow Lights” (2016)

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.

Light spectrum that can be modified and tailored endlessly

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.

Programmable and reprogrammable lighting scenarios

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.

Figure 2: Drag and drop recipe zones. Source: Sollum Technologies (2021)

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.

Responsiveness to ambient Light

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.

Figure 3. Sun’s spectral progression in Montréal during the afternoon of April 15, 2020. Source: Sollum Technologies (2021)

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.

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.

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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.

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.

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