Magnetic Ballasts: Watts In The Box?

Growers! Sit down—especially if you’re prone to getting angry easily. I’m afraid that I have some frustrating news—for some of you at least. You might want to take the weight off your feet before reading on. There’s no easy way to break this, so let me just wade straight in…

This news concerns ballasts—magnetic ballasts, to be precise. We have some very serious quality issues to explore—and no, before you ask, this isn’t some thinly veiled attempt to up-sell you to the new electronic/digital variety. (They can have their own problems too, but that’s for another time.) For now, let’s just focus on those trusty stalwarts of indoor gardening—600W magnetic ballasts.

Why 600W? Well, they’ve been the mainstay of European indoor gardeners for decades now and for good reason. 600W high-intensity discharge grow lamps (HIDs) offer slightly higher efficiency than their 1000W big brothers and, while they’re obviously not as intense, they’re widely regarded as more grower friendly. Therefore it’s no surprise that if you walk into any grow room in the UK, France, Spain, Holland or Germany, you’ll most likely be greeted by a fleet of reflectors housing trusty 600s.

Now, I’d be the first to admit that magnetic ballasts are probably not the sexiest-looking pieces of kit in your set-up, especially when compared with all those exotically labelled nutrients and additives. As such, these dull, heavy boxes tend to get fixed out of the way (good idea!) and overlooked. As long as our grow lights switch on every day most of us don’t give our ballasts a second thought save for a quick dust-wipe every so often. (Another good idea!)

Of course, the majority of growers have at least a vague idea of the function their magnetic ballasts (aka ‘chokes’) perform. You probably already know that they act both as ignitors of your grow lamps and as electrical capacitors. Simply put, your magnetic ballast is responsible for creating impedance that provides the correct power to the lamp.

Here, perhaps, lies the kernel of the problem. Most growers don’t realize when their ballasts aren’t working as they should unless the problem is obvious—i.e. the lamp fails to light, persistently flickers or explodes! This leaves a whole spectrum of potential quality issues that, for the most part, are completely lost on the average grower—and many retailers too. It’s this ignorance (sorry, there’s no politer word) that allows unscrupulous manufacturers the opportunity to exploit us.

Brace Yourself for the Horrible Truth!

You might expect two different 600W magnetic ballasts to perform the same (i.e. they send the same amount of electrical power to the lamp) with give or take, one or two percent maybe. However, as the indoor gardening market has expanded, the “race to the bottom” in terms of price and quality has also intensified. Regrettably, our desire for a bargain has encouraged cheap, inferior equipment onto the shelves of some of the less discerning grow shops. Magnetic ballasts are right at the top of the list. As a result, a surprising number of you reading this will be running magnetic ballasts that aren’t driving your lamps properly and, as such, you are being cheated out of potential yield, crop after crop, no matter how often you diligently change your lamps.

How bad is the situation? Really bad! A genuine 600W ballast actually draws around 655W at 240V from the mains supply. Those extra watts are lost mostly to heat, and it’s perfectly normal. The important thing to note here is that a true 600W ballast delivers 600W of power +/-3% to the lamp. In tests endorsed by a major European lighting company, some brands were found to be under-powering lamps by up to 15%! Yes, you read that right. Your “600W” lamp might be receiving just 512W at best. Of course, this deficiency in watts massively reduces light output, at 512W this equates to 40% less light from your lamp, and every photon less your plants receive directly corresponds to less energy driving growth and bloom. But this is just the tip of the iceberg!

Bad Ballasts Create Serious Side-Effects

Your magnetic ballast is, quite literally, the powerhouse of your garden. In fact, I’d argue that there’s no more important gear than your ballasts! Sure, water quality, nutrients, lamps, reflectors, growing media, ventilation, and environmental controllers all play their part in the modern indoor grow set-up too—but their role will always be secondary to the quality, and quantity of light energy you bring into your garden. This is pure and simple science! Light is the first order of life itself. So, if your ballast is under-powering your lamp by X%, you don’t need a Ph.D. in photo-biology to figure out that this equates roughly to X% less energy available to your plants. No amount of hocus pocus with the latest over-priced (and heavily marketed) “Buddy-Gorilla-Juice” is going to make up for this fundamental shortfall.

Less energy input into the indoor garden machine means less productivity!

However, as I’ve already implied, under-powering your grow lamps presents more complex and less intuitively obvious consequences. HID grow lamps use a very specific mixture of chemical elements that turn into light-emitting plasma when electricity is passed through them. Different elements give off different colours and turn into plasma at different times as the lamp fires up. (You’ve probably seen this for yourself many times as your lamps warm up.) To achieve the right spectrum (the one the lamp manufacturer intended—i.e. the spectral distribution that drives photosynthesis most efficiently) the lamp needs to receive its full quota of power. Put another way, it’s the combination of all the different colour elements that deliver the right spectrum of light to properly drive growth and bloom. So, 25% less power to your grow lamps doesn’t just mean 25% less light (as if that wasn’t bad enough!)—the whole spectral distribution is sent out of whack. Metal halide lamps, in particular, produce far higher levels of “green light” when underpowered. (And, in case you forgot, green is the colour that plants don’t use.) Not only could your plants be receiving less light, but they’re receiving the wrong colours too. Talk about a total waste of time and energy!

Core and Coil: It’s All About Insulation!

So how can you tell a genuine 600W ballast from a piece of junk that under-powers your lamps? First, let’s look at a ballast in more detail.

Magnetic ballasts aren’t exactly space-age technology. Maybe that’s why, when they’re manufactured correctly, they are so reliable! Rather than bore you with “Ballasts for Beginners” let’s just take a look at the key components where shortcuts are commonly taken.


Every magnetic ballast has a windings coil. This is a coil of winding wire, similar to cotton on a bobbin or reel. A magnetic field is generated and this is a key part of regulating the current to the lamp. In order to function properly as an electrical inductor, it is imperative that the differential between each layer stays constant, and never breaks across between rows.

The winding wire used in magnetic ballasts can be one of two grades. The low-grade conductor material (either copper or aluminum) has a single coating of insulating resin. The higher grade uses two coats—it’s said to be “double processed”. (No prizes for guessing which grade the cheap, sub-standard ballasts use!) The quality of the winding wire makes a difference to the overall performance because of the aggressive environmental influences a magnetic ballast is subjected to—high temperatures, high voltages and high currents. The higher grade winding wire is crucial otherwise it can quickly start to break down.

High-quality magnetic ballasts also use a process called “precision winding”. This means that each and every turn (and layer) of winding wire is precisely wound so that each wire runs perfectly in-line and uniformly parallel to its neighboring wires. By comparison, lower quality ballasts simply scramble the wire chaotically around the winding reel.


Thin pieces of electrical steel are also used in the manufacture of magnetic ballasts. Each piece must be individually coated with insulating material. Together, these pieces form into a steel core that passes through and around the winding coil. The quality, type, and specification of this electrical steel lamination are all important to the overall efficiency and compliance with European standard criteria. Poor quality or inadequate specification grade laminations will result in inefficiency, overheating, and noise (both audible noise and ‘harmonic’ distortion leaking back into the mains power supply).

Vacuum Impregnation

Finally, the epoxy-polyester resin material used to give additional insulation to the ballast must be both of good quality and vacuum impregnated. The ballast is submerged into a bath of epoxy-polyester resin within a chamber that forms a complete vacuum by sucking out all the air—the resin is pushed into all the nooks and crannies. Only then can the thermal and insulation properties of the ballast be considered truly up to the task! Of course, this is a costly and timely process so it’s sometimes skipped altogether.

Substandard ballasts not only cut corners in some or all of the aforementioned areas but, as a result, they run inefficiently, drive the lamp poorly, and tend to have far shorter lifespans. To counter the natural side effects that these quality issues incur, manufacturers purposefully design their ballasts to operate at lower currents and lower lamp power. This masks the presence of low-quality components but delivers very poor lamp performance as a result—crucially this is not readily discernible to the human eye.

Understanding Ignitors

The ignitor is the other critical component in a ballast. As the name suggests, it is responsible for initially lighting the lamp by creating a high voltage pulse between the two electrodes in the lamp. As we touched on earlier, it’s this arc that forms across the internal arc-tube gases that carries the electrical current through the lamp itself. The ballast controls the flow of this current. If the ignitor is high spec and high quality it will have a built-in timer to avoid continuous high-voltage pulsing in the event of a missing or failed lamp. This will be matched and designed in conjunction with the ballast. Many of the substandard magnetic ballasts use ignitors that are crude in both their design, and the manner in which they strike the lamp. They have no timer and are vaguely, and inefficiently matched to the ballast. Because these systems are used to strike and operate the lamp at distances of up to six to ten metres from the power-pack, it’s imperative that the ignitor is matched correctly to its ballast. The ignitor uses a section of the ballast’s coil to boost its voltage (like a step-up transformer), and therefore, the ballast will see the full 4.0-5.0kV voltage pulses.

It is important therefore that the ballast, its materials, insulations and overall construction are robust and of the highest quality to ensure safe and reliable ignition and continued operation.

A Quick Word Concerning Capacitors

The capacitor is a device that sits across the mains supply and corrects the power factor. It basically shields the ballast from the peaks and troughs in the mains power supply. A poor quality capacitor will draw wastefully high currents from the supply and may be constructed with low quality (and low cost!) dielectric film—the essential component of the capacitor. This quickly degrades and begins to draw higher currents from the mains. Sometimes low-quality capacitors can fail violently too!

The Grower is the Ultimate Loser

So, we’ve seen that there are a whole lot of potential corners that can be cut when manufacturing a magnetic ballast. In addition to the winding wire, lower grade electrical steel can be as much as 80% cheaper than European standard compliant electrical steel. Manufacturers can also save big time on foregoing proper insulation pieces, and epoxy-polyester resin vacuum impregnation, and timer control for ignitors. Throw in a low-cost capacitor, and what you end up with is a notional magnetic ballast that’s clearly not fit for purpose—even downright dangerous to use!

How To Avoid Being Ripped Off

So now you’re probably thinking: all this information is great on a theoretical level, but how do I use it practically to discover whether I’m inadvertently running one or more of these substandard ballasts or to avoid wasting money on one?

Three Practical Things You Can Do:

Thankfully, the reputable, established manufacturers are getting together to protect you—and their brands! Look for the “Genuine power” and “Genuine Quality” seal of quality on the ballast packaging. You can find out more by visiting: www.genuinequality.co.uk.

Leave a Comment

Your email address will not be published. Required fields are marked *


Everest Fernandez is a well-respected industry educator, veteran hydroponic grower, and grow light enthusiast based in France. He works primarily as a marketing and cultivation consultant and was the founding editor of Urban Garden Magazine in the UK, US, and Canada. He also writes and researches for the popular hobby horticulturist YouTube channel, Just4Growers.