Control Freak: How to Regulate Your Garden’s Artificial Lighting

By Darryl Barry
Published: February 18, 2020 | Last updated: December 7, 2021 11:15:34
Key Takeaways

Indoor greenhouses are illuminated by artificial lighting that is required to be on and off for many hours of a day or night. Controlling this lighting can be a big job, but thankfully we have some help.

Source: Lane Erickson/

Controlling a grow room’s lighting requires the use of electrical controllers built to handle four to 100+ lights. Power requirements might even require the indoor greenhouse to be powered with three-phase power, single-phase power with a 200-A service or something even larger.


A lighting controller consists of contactor(s), 120-V or 240-V receptacles, a timer or trigger cord and breakers. Many companies sell these pre-assembled with everything contained in one enclosure, which is easy to mount and wire into the building’s main power. If you have the money, you can even hire an electrician to custom-build your lighting controllers and load centers.

It’s also easy to mount a load center with several breakers (some for 240 V and 120 V), which is then connected to another enclosure (which is NEMA rated) with an electrical metallic tubing pipe.


This set-up is National Electrical Code (NEC) compliant, and mounting two separate enclosures is also safer and easier to service any of the contactors, relays, timer, programmable logic controller (PLC), high-temp shut-offs, printed circuit boards and any other electronics or parts mounted inside. Still, remember that when you are servicing a load center, you might be required to turn off the power before removing the load center’s cover.

With larger load centers (100 A or more), a main breaker is a must-have. This way, in case of emergency, all the power can be shut off by switching the single main breaker as opposed to ten or twenty individual ones.

The main power supplied to your indoor greenhouse will be either single-phase or three-phase. In commercial buildings, it is more likely to be three-phase, which can be either a WYE or High-Delta. Installing dozens of lights in a three-phase location can be tricky to balance the loads across all three legs of the power system.


Read More: Three Considerations to Make When Designing Growroom Lighting

The voltage across two legs will be either 240 V or 208 V. In a High Delta three-phase, the second leg is not 120 V to ground, it’s 208 V—so, if a 120 V device is ever connected to this second leg, it will be burned out.


Also, make sure that your ballasts are wired for the correct voltage. Electronic ballasts have operating voltages from 90 V to 240 V. Coil and core ballasts have multiple input voltages for the transformer, so make sure the ballast is wired for the correct voltage on three-phase power to make sure it works correctly.

Some electronic or digital ballast also now feature dimming levels for the lights, which reduce power consumption as well as light levels and temperatures. Indeed, heat can be a major problem in greenhouses.

As such, a controller’s breakers and heavy-duty contactors should be separated so that the heat generated by the contactors does not affect the breakers as it can trip due to high temperatures. If your load center is located in an area that gets warm (above 100ºF), this can affect the breakers too.

Another way to reduce heat in a greenhouse without sacrificing light levels is to turn about 10% of the lights off when temperatures rise too high. Each time this is done, the lights can be sequenced to make sure that they cycle, instead of having the sames one stay lit each time. A chessboard pattern would be the easiest to manage, and a load center or controller can be built to shut off the different lights each time the temperature rises.

Keep in mind though that today’s off-the-shelf lighting controller won’t allow custom lighting controls. An electrician needs to be hired to build a controller with PLC options that can handle all the lighting control and protection.

A simple PLC can have eight input triggers and four outputs to control four contactors or ballasts. It can also have a simple timer board for four lights or ballasts, with four input triggers and four outputs.

Then, if needed, the ballasts can be programmed with on and off delays, from 1/100 second to several minutes—all programmable down to seconds. The four input triggers can be plugged into a timer, heat sensor, flood detector, etc.

Each of these input triggers would control the number of ballasts or lights to turn off or on in the event of activation. For example, a smoke detector could shut off all lights or ballasts immediately, while a temperature controller could turn off and on one or two lights a few times a day when the temperature rises.

More complex PLCs can control everything from hundreds of lights to AC, fans, heating, CO2, pumps, sensors, etc. It can also control the ballast dimming levels via time schedules or temperature settings. (A touchscreen makes it easier to change the PLC parameters or time cycles.)

Read More: Keeping Things Cool in Your Growroom

If there’s ever a concern about how many amps are being drawn when all of the devices are on, even intermittently, some digital ammeters can be installed to monitor power in real-time.

With larger indoor gardens, a flip is sometimes used to create opposite 12-hour cycles in two separate rooms of flowering lights. There are several off-the-shelf flips, which all have the same layout, or an electrician can also easily build you an NEC-compliant flip. If you have two separate growrooms, then the lamp cords should be plugged into opposite sides of the flip enclosure.

You can also link the flip to your load center to allow the off and on cycling of ballasts as required when lights are flipping from either side. When a PLC is installed in a flip, multiple-timing cycles and individual flip relay control is achieved. Even if the lights are flipped every hour (to allow a vegetative cycle in both growrooms), the ballasts can still be powered off and on—for even a few seconds to a few minutes—and stagger the delays in between.

There are several models of lighting controllers available off-the-shelf that are safe and reliable, but always check with local electrical inspectors before you install. Even though they may have an ETL marking, you need to inquire as to what the ETL listing is for. It might just be for the components inside and that all of the components are UL-tested, CSA-tested or listed.

Ask if the UL or CSA rating applies to the controller as a whole and if it has a UPC code. A lighting controller needs an ETL listing and to be in compliance with NEC guidelines and policies for building and installing electrical devices.

Both of these guidelines are government regulated, and inspectors have to ensure that all the power and appliances are all built safe and reliable. If you have the money, find a local licensed electrician to build a load center and controller unit that will be easy to mount and is 100% compliant and customizable.

Read Next: Tips and Tricks for Properly Sealing Your Growroom


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Written by Darryl Barry

Profile Picture of Darryl Barry
B.C. native Darryl Barry has been involved in the hydroponics industry since 2004 when he began building timers and flips for local hydroponics stores. Feeling that there were no quality products on the market he began building his own timers and controllers. Darryl has attended the College of New Caledonia, BCIT, and the Granton Institute of Technology and has over 25 years of experience in commercial and residential wiring, professional sound and special effects lighting, industrial and home automation, alternative energy and security systems. Darryl is the owner of No Wire Nuts, a home-based well equipped electrical shop located in New Westminster, B.C. where he currently resides with his dog Olyver. Darryl can be reached at [email protected]

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