Light is a critical element in any controlled environment. Plants need the ideal amount of light based on their type, growth stage, and other environmental factors.

To achieve this, growers must rely on both natural and artificial light. Ensuring we provide the right amount of light is expensive, regardless of the source, and producing light is the result of generating electricity in some way.

By automating the growing environment, growers will fine-tune light delivery, which will translate into more sustainable and efficient operations.

Most integrated environmental control devices can make near-instant adjustments to the device in response to changing sensor information, predictive algorithms, and programmed logic responses.

Generally speaking, automation controllers are much more responsive than equipment at telling equipment components what state they should be in.

Even if the device can respond immediately, there is little benefit in doing so, as excessive on/off cycles can limit the life of motors, switchgear, and lamps.

A properly tuned integrated climate control system responds to changes in the environment in a diminished or attenuated manner, balancing the need to maintain a set point with the need not to overuse equipment or exceed responsiveness.

Although the Sun’s spectral mass is constant, it varies widely in intensity, duration (daily and seasonal), and direction.

A number of strategies, including shading and supplemental lighting systems, have been developed to deal with adverse indoor production conditions associated with light fluctuations.

Sunlight conditions in a greenhouse change rapidly, affecting temperature, humidity and illuminance.

To compensate, greenhouse ventilation, heating, shading, irrigation, humidification and lighting must respond reasonably to these fluctuations if a controlled growing environment is to be achieved.

This requires good engineering and proper selection of equipment and controls. It also requires an understanding of the capabilities and limitations of greenhouse equipment systems, sensors and controllers.

Controlling how much light a greenhouse crop receives can be influenced by two main methods: shading and supplemental lighting.

shadow control

For fully sun-tolerant crops—such as tomatoes, cucumbers, and chrysanthemums—shading is never needed to limit PAR levels.

With proper domestication, these crops are fully capable of withstanding and harnessing the full power of the sun. However, it is often necessary to provide shade to limit heat build-up in the greenhouse air and leaf surfaces.

Also, if used with care, some interior shading systems can be partially effective in helping to reduce vapor pressure deficits on bright, hot days. For low-light crops and special applications (eg rooting cuttings), shading is necessary to limit total solar radiation. Some typical control parameters that can be used to operate a shading device include:

• Time (absolute or relative to day length and season)
• Global Light (from outdoor sensor)
• Temperature (outdoor and/or indoor)
• Humidity (set point)
• Light cycle programming (for blackout screens)

Other parameters that can be used to control the behavior of shading devices include phased opening and closing strategies, special overlays for events such as snowfall, spraying operations, and synchronization with heating, ventilation, humidity control, and carbon dioxide replenishment. The most flexible control program allows multiple parameters to be integrated simultaneously.

Supplemental Lighting Control

Greenhouses in some large installations may not have enough power service to operate all the lights at the same time, so they may need to be segmented based on the power available.

When using the integrated controller, the operation of the auxiliary lighting system can be controlled by several parameters, including:

• Cyclic lighting (for photoperiod control)
• Supplemental Lighting Duration Control
• Light
• Integrated Insolation Level (DLI)
• Instantaneous radiation set point
• CO2 synchronization

Cycling lighting is typically only used with incandescent lamps, providing photoperiod control only by cycling through a series of relatively short-duration lighting cycles at night.

By using this method, less overall lighting time and power consumption can be used compared to traditional long-day lighting. It is not recommended for use with HID lighting as these lights are not designed for frequent riding.

lighting control

For supplemental lighting, regardless of the control method used, it is best to operate the lamps for extended periods of time, as the short-cycle cycling of these lamps can greatly reduce lamp and ballast life.

Therefore, when programming based on the instantaneous or cumulative light energy available, it is best to set some conditions to prevent cycling.

These may include verification times, during which the need to turn the lights on or off must be maintained for a desired period of time. This prevents the lights from cycling on and off in partly cloudy weather.

Another way to prevent looping when using light-based control is to provide minimum on and off time overrides.

Other additional strategies can be used alone or in combination with the above strategies. For example, to get the most value from supplemental carbon dioxide, there must be adequate light levels.

A separate program can be established to ensure that crops always receive minimum light levels during CO2 supplementation.

automation In addition to the proper use of special programs available on state-of-the-art environmental control systems, the use of shading and supplemental light will contribute to more efficient and sustainable planting practices.

Using sensors, adjusting set points, and understanding your goals will help develop more consistent products while ensuring optimal use of resources.

_{Alex Fermon is Product Marketing Manager Argus Control. Text part adapted from “Lights and Lighting Controls in Greenhouses” by Argus Controls. Argus Controls and Conviron are Sustainable Cannabis Coalition. Image via Argus Controls.}