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To spread the light more evenly across your crops, a reflector is often used. A ballast is generally connected into a compatible reflector before the bulb is installed. Ballasts create a certain amount of heat, depending on the type.
There are generally three broad categories of ballasts: magnetic, digital, and electronic. These categories relate to how the ballast keeps your type of light aglow. Don’t get too caught up in the mechanics of it, but the basic differences and explanations of the different types follow below.
Magnetic ballasts have been around for a while and are the largest and least efficient of the three types. Magnetic ballasts can be thought of as electromagnets inside of thick metal or heavy plastic canisters or boxes. They generate the needed energy by way of a large spool of wire surrounding steel sheets. The current created is then sent to a single induction coil. Capacitors then regulate and maintain the voltage at the level needed by each light. These are the types of ballasts often found in greenhouses that have been in operation since the middle of the 20th century, especially those using fluorescent grow lighting. They are usually the cheapest of the three systems as well.
(Want to know when to switch to digital? Is It Time to Upgrade Your Magnetic Ballasts to Digital Ballasts?)
Electronic ballasts, as the name implies, do not require a magnet, but rely on semiconductors, microchips, and other electronic components to regulate and supply the required voltage and watts needed. They are usually considered superior to magnetic ballasts for these reasons:
The digital ballast is often confused with the electronic ballast. A digital ballast can be thought of as a smart electronic ballast as it is governed by microprocessors. Digital ballasts can perform the same functions as electronic ballasts but are able to offer a higher level of precision as to when and how much power to deliver. They also ensure a more reliable and consistent operation and can log information like temperature, lamp voltage, etc. Digital ballasts, like electronic ballasts, are dimmable, but where electronic ballasts are dimmable in 100- to 400-watt increments (though they can be built to have more steps), digital ballasts can be dimmed to land at any point between 400 and 1,000 watts to achieve a more appropriate amount of illumination for the crop being grown. These are often the most expensive type of ballast. It should be noted that electronic and digital ballasts are not interchangeable. Switching to one or the other type of bulb will usually require an entire system upgrade.
Now that we got the technical stuff out of the way, let’s look at the ballasts used for different types of grow lights. If you are using LEDs, then the lights are built into a board and the following information is not relevant. If, however, you are using any type of high intensity discharge (HID) bulb or fluorescents, the differences outlined below may help inform your decision about which type of ballast to look for.
Within the range of HID ballasts are those that accommodate HPS, MH, and ceramic metal halides (CMH). Ballasts for any of the HID lights can regulate current very precisely.
Ballasts for HID lighting are complex and dynamic. They are built to perform a range of tasks specific to the smooth operation of HID bulbs. They are also built to avoid overheating while turning on and off thanks to the special circuitry installed within HID ballasts. These facilitate the cooling of xenon gas before getting the jolt of high voltage needed to turn the light back on.
Ceramic metal halide bulbs are a special type of MH bulb and require a different type of ballast. These ballasts put out very low frequencies and, therefore, are not often found on electric ballasts. This is not always the case, however. Some higher-end electronic ballasts can support CMH lights because they have been installed with microprocessors to avoid problems with the interference. Most CMH ballasts, however, come as a kit with the bulb and a reflector so the problem of matching bulb to ballast is avoided.
Double-ended (DE) ballasts are a type of ballast for HPS and/or MH bulbs. These ballasts support bulbs that produce highly luminous light as a result of the combination of mercury gas and metal halide. This combination produces up to five times the light of a similarly sized incandescent lamp and more light on the spectrum of natural light than HPS lamps. Double-ended lighting and ballasts are popular with many growers due to their longevity, reliability, and efficiency.
Ballasts for fluorescent lighting come in numerous types as well to expand the array of available choices. There are programmed ballasts, rapid start ballasts, and instant start ballasts for fluorescent lighting. In all cases, the ballast supplies the needed voltage to start and regulate the current to ignite and keep the light output steady. Without a fluorescent ballast, the useful life of the bulb would be greatly reduced as it would draw too much power and burn out.
Programmed Ballasts — These ballasts supply energy to the bulbs once the electrodes or cathodes inside have warmed enough to power the light. This gradual start prolongs the life of not only the bulbs, but the entire fixture. The programmed ballast follows a sequence to start and operate the bulbs. With little variation, the ballast will first initiate a preheating stage. After sufficient current is present, the next step is to supply higher voltage throughout the lamp to establish an arc that produces the glow from the bulb that we are all familiar with. Some high-end programmed ballasts can go from step one to step two in well under one second. The main advantage to the programmed start ballast is the ease in which the bulb is activated — it will allow for many tens of thousands of starts per bulb. The cost of this longevity is that they take longer to light up and may flicker in the process, meaning that your plants will not get the full spectrum of light at the first flip of the switch.
Rapid Start Ballasts — These ballasts are not vastly different, but as the name implies the lamp lights up sooner than with programmed ballasts. In rapid start ballasts, the electrodes are preheated in the starter, which still reduces the voltage needed to start the light, but it can essentially light up almost as soon as it is turned on without risking the bulb’s longevity. Bulbs in a rapid start ballast will not last quite as long as with programmed start ballasts but will last longer than with instant start ballasts.
Instant Start Ballasts — These ballasts require higher voltage than either the programmed or rapid start ballasts but will allow for fluorescent bulbs to light up (you guessed it) instantly. These types of ballasts can be more efficient than other types, but only in applications where the bulbs are not frequently turned off and on. Growers that only turn their lights on once per day may do well with instant starts, but if the photoperiods are micromanaged with numerous starts and stops, the instant start ballast will go through bulbs much quicker than its counterparts.
If all of this still serves only to confuse you instead of giving more clarity on the choices of ballasts out there, don’t fret. Decide what you want to grow first. Determine the characteristics of your grow space. Decide what aspects appeal to you most. Is it initial start-up cost? Prolonged energy savings? The quality of the light that you want? Once you have these figured out, the choice of ballast may fall into place more easily. Visit your local garden, hydro, or grow store with the answers to the above questions and they will most certainly be able to help you select an appropriate ballast for your light type, grow space, and crop.
Source: Maximum Yield December 11, 2018 "Choosing the Right Lighting Ballast For Growing" https://www.maximumyield.com/choosing-the-right-lighting-ballast/2/17434
