Lighting and curtain technologies curb light pollution, stabilize greenhouse climate
January 20, 2021 By Greenhouse Canada
Ontario greenhouse growers are facing a new, serious challenge: local light pollution bylaws, and the impact of these measures on their crops.
“While nuisance regulations that protect property rights are not new, the greater adoption of supplemental lighting is getting the attention of both neighbours and municipalities,” says Kurt Parbst, director of business development at Envirotech Cultivation Solutions. “Bylaws are being adopted and considered in Canada – as well as the U.S. – that create a guiding framework that actually help protect neighbours and growers. While having rules or a defined minimum standard is helpful, it creates some technical challenges.”
Leamington is following in the footsteps of Kingsville, Ont. council for a bylaw on light pollution, ordering that light cannot cause a nuisance by shining on neighbouring properties or into the night sky.
Because of this new Greenhouse Light Abatement Bylaw, growers must keep ceilings, sidewalls and end walls completely covered with curtains from one hour before sunset to one hour after sunrise. Ceiling curtains must be at least 90 per cent closed between 2 and 6 a.m.
Some of the requirements for Leamington growers will include:
- Greenhouses must have sidewalls and end walls installed and operational by April 1.
- The ceiling curtains must be up by October 1. (In the interim, operators without curtains must shut out the lights from 8 p.m. to 2 a.m. starting in January.)
“We know that grow lights emit light and heat into the greenhouse and plants transpire in response. Temperature and humidity levels elevate beneath a curtain or screen that is intended to reflect light back to the crop and prevent transmission to the sky,” says Parbst. “It is important to select a screen that has high light interception but reasonable heat and humidity transport via the ‘tightness’ of the woven pattern and capacity of humidity transport yarns. If high humidity and temperature persist, the resolutions are either gapping the screen or actively ventilating beneath the screen, which are less than ideal.”
Another method is simply to reduce the total amount of energy that is introduced beneath the screen via lamp selection, keeping lamp electronics cool with a water circuit which allows a significant amount heat to be transferred out of the growing area.
“This separation of light and heat ensures a high photosynthetic growth rate, while unwanted heat transpiration is avoided. This is a powerful tool,” says Parbst.
“In most discussions we have, the biggest challenge that growers face is the need for gapping the screens to let the heat from the HPS lighting out,” says Tyler Rodrigue, director of sales and projects at Westland Greenhouse Solutions. “This is greatly reduced when working with water-cooled LED fixtures and proves to be very beneficial to the grower. When a grower in these regions is thinking about switching from HPS to/or starting with LED, they should consider the technical benefit of actively cooled LED grow lights.”
One company’s water-cooling technique extracts the heat from the LED fixtures, and transfers it out of the growing area via the cooling water circuit. Heat and light are de-coupled and the climate becomes more stable and controllable.
For every ~1,000W that is introduced via the lamp approximately 350W of heat can be removed, avoiding a transpiration response. A bonus is that the gained heat can be reused.
The light output is extremely high and because of the continuous cooling, the lifespan of the fixture and the diodes is extended, and the light output is guaranteed to be more consistent over the years (L90 B05 – 50,000 hrs), according to the manufacturer Oreon.
Canadian cannabis grower Medisun has been using Oreon’s LED grow lights since 2018.
“It gives us short and more compact crops with improved THC/CBD potency compared to HPS lamps and it makes it feasible to complete one extra cycle per year,” says Laust Dam COO at Medisun. “The biggest advantage is the water-cooling that keeps our greenhouse climate stable. We can keep windows closed and keep CO2 and in particular odour inside, a common problem for cannabis growers.
Medisun’s blackout curtains are used for control of daylength but also for avoiding light pollution. For Dam, the benefit of the Oreon lamps comes when they have to close the blackout curtains.
“The water cooled fixtures do not add extra heat to the greenhouse and as venting is limited with traditional greenhouse vents when the blackout is closed, we can still keep the crop at required temperature and humidity,” says Dam. “With other light sources, like HPS or LEDs without the water cooling ability, (it) would require other ways of active cooling or ventilation and require abundance of more energy to keep same temperatures and humidity levels.”
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