Light is a key element in any controlled environment. Plants need an ideal amount of light depending on the type of plant, the stage of growth and other environmental factors.
To achieve this, producers must rely on both natural and artificial light. Regardless of the source, making sure we provide the right amount of light is expensive, and generating it is the result of some way of generating electricity.
By automating the growth environment, growers will adjust their light delivery which will result in much more sustainable and efficient operation.
Most integrated environmental control equipment can make near-instantaneous adjustments to equipment in response to changing sensor information, predictive algorithms, and programmed logic responses.
In general, automated drivers are much faster at telling computer components what state they should be in than what the computer can respond to.
Even if the equipment could respond instantly, it would rarely be beneficial to do so, as excessive on and off cycles can limit the life of motors, gears, and light fittings.
Properly adjusted integrated climate control systems respond to changes in the environment in a humid or attenuated manner that achieves a balance between the need to maintain setpoints and the need not to overload the equipment or exceed the degree of answer.
Although the spectral quality of the sun is constant, it is highly variable in intensity, duration (daily and seasonal) and direction.
Many strategies have been developed, such as shadow systems and supplementary lighting, to deal with the undesirable indoor production conditions associated with fluctuating light.
Sunlight conditions in greenhouses can change quickly, affecting temperature, humidity and lighting.
To compensate, the ventilation, heating, shade, irrigation, humidification and lighting equipment of the greenhouse must respond reasonably to these fluctuations if a controlled growth environment is to be achieved.
This requires good engineering and proper selection of control equipment and devices. It also requires an understanding of the capabilities and limitations of greenhouse equipment systems, sensors, and controllers.
The control of the amount of light received by a greenhouse crop can be influenced by two main methods: shade and supplementary lighting.
Shading control
For full sun tolerant crops such as tomatoes, cucumbers and chrysanthemums, shading is never required to limit PAR levels.
Properly acclimatized, these crops are perfectly able to withstand and use all the power of the sun. However, there is often a need to provide shade as a means of limiting heat buildup in the greenhouse air and leaf surfaces.
In addition, some internal shade systems, if used with care, can be partially effective in helping to reduce the vapor pressure deficit on bright, hot days. For low-light crops and special applications such as root cuttings, shade is used as a necessary means to limit total solar radiation. Some typical control parameters that can be used to operate shadow equipment include:
- Time (absolute or relative to the length of the day and the season)
- Global light (from external sensors)
- Temperature (outside and / or inside)
- Humidity (setpoints)
- Photoperiod programming (for opaque screens)
Other parameters that can be used to control the behavior of shadow devices include staged opening and closing strategies, special cancellations for events such as snowfall, spraying and synchronization operations with heating, ventilation, humidity control. and CO2 supplements. The most flexible control programs allow the integration of several parameters at once.
Additional lighting control
Some greenhouses with large facilities may not have enough electrical service to operate all of their lights at once, so they may need to be staged according to the available electrical power.
When using integrated controllers, it is possible to control the operation of the additional lighting systems by means of parameters that include:
- Cyclic lighting (for photoperiod control)
- Additional control of the duration of the lighting
- Light
- Integrated daily light levels (DLI)
- Instant radiation setpoints
- CO2 synchronization
Cyclic lighting is typically only used with incandescent lamps only to provide photoperiod control through a series of relatively short lighting periods at night.
With this method, it is possible to use less global lighting time and electricity consumption than with conventional long day lighting. It is not recommended for use with HID lighting, as these luminaires are not designed for frequent cycling.
Lighting control
For additional lighting, regardless of the control method, it is best to operate the lights for extended periods, as a short cycle of these luminaires will greatly reduce the life of the lamp and ballast.
Therefore, when setting up programs based on the instantaneous or accumulated light energy available, it is best to set up some conditions that prevent cycling.
These may include a trial time, where the need to turn the lights on or off must be maintained for a desired period. This prevents the lights from turning on and off in partly cloudy weather.
Another method of preventing cycling when using a light-based control is to provide a minimum replacement for the on and off time.
Other additional strategies could be used alone or in conjunction with the above. For example, to get the most value from CO2 supplementation, you need to have adequate light levels.
A separate program could be established to ensure that crops always receive a minimum level of light during periods of CO2 supplementation.
Automation additional shade and light, in addition to the proper use of special programs available in the most advanced environmental control systems, will contribute to more efficient and sustainable cultivation practices.
Using sensors, adjusting setpoints and knowing your goals will help you grow a more consistent product while ensuring optimal use of resources.
Alex Fermon is the Marketing Director for Alex Fermon Argus controls. Text partially adapted from “Light and lighting control in greenhouses” by Argus Controls. Argus Controls and Conviron are founding members of the Coalition for Sustainable Cannabis. Images from Argus Controls.
