I’ve chosen to write about high intensity discharge (HID) lighting now because these lights still have a place in the home grow. HID lights come in several flavors such as; metal halide (MH), high pressure sodium (HPS), compact metal halide (CMH), and double ended high pressure sodium (DE HPS). HPS and MH have been the most common traditionally and may be worth considering because you can get used units cheap! A google search will yield piles of results with lengthy discussions on these technologies. For our purposes, I’ll focus on the topics most relevant to small home grows.
When purchasing a used HPS or MH unit, it’s important to inspect if carefully. These units consist of several individual pieces; the hood (reflector), the bulb-socket and cord-set, and the ballast. Reflectors can be visually inspected for defects. Be sure to ask for the glass lens for it as well and ensure it is free of excessive scratches. Visually inspect the cord-set and bulb-socket as well. It should be free of cracks and other physical problems. As for the ballast – this part should be inspected by someone qualified to do so. Ballasts will hum, but if that hum seems too loud, there might be an issue. Do NOT skip having that ballast inspected.
The real downside of HID lights is the heat production. Most will produce at least double the heat of a comparable LED. This, in turn, will double your cooling costs during the summer. In addition to the heat produced by the power consumption, HID lights also produce infrared radiation which will not only heat up the surfaces of your leaves, but other objects in it’s path including walls and floors. You can really feel that extra heat when you place your hand under the light.
You will need to vent these lights and your space, particularly when the space is small. Placing the ballast outside the space will help, and using build-in ventilation ports on the reflector will also help (this is what the lens is needed for). However, that IR radiation will pass right through the lens so you can count on needing to vent the space or including air conditioning directly in the space.
The light intensity a HID produces is great, there is no doubt about it. Award winning cannabis has been grown under these lights many times over. However, that intense light can burn plants up in a hurry. A tall ceiling or short plants may be needed in order to keep the lights far enough away from the plants to prevent light burn. Couple light stress with the potential heat stress and you’ve got a real plant killer. More than any other setup, you should dial in the environment within a grow space equipped with HID lighting – before adding plants!
HID lighting can also be sensitive to power interruptions. It is not good for the bulb and ballast to turn off the unit and immediately turn it back on. This is referred to as a ‘hot start’ and can ruin a rather expensive bulb and/or electronic parts in the ballast. To remedy this I always recommend a 15 minute lighting delay timer. When the power flickers, this device will keep the power off for 15 minutes to allow the components to cool enough for a normal start. Yes, this means that every time your power flickers (think thunderstorm) your lights will be off for 15 minutes. Some growers state that there has never been such a problem for them, but others have popped many bulbs and have had expensive ballast repairs due to the same. Do you have a backup bulb?
Finally, you will need to clean lenses as often as weekly, and dust off your bulb as well, particularly if the hood is vented. Settling dust can greatly reduce the light production. Bulbs should be replaced per manufacturer recommendation. Weak light production can cause weakened plants, which invites pests.
Do you have tips for new growers using HID? We’re love for you to leave them in the comments.
Happy Harvests!
— The Lit Farmer —