Everest runs through the pros and cons of using air-cooled reflectors.
Air cooled grow lights seem to polarize growers. Some gardeners swear by them, whereas others claim they're doing just fine with their regular hoods.
As for me, I can see cases and applications for air-cooled grow lights and where they will definitely make your life easier. At the same time, I'm a big fan of keeping things simple wherever possible! (My mother's good advice!) - So here is, I hope, a balanced overview of the pros and cons of air cooled hoods. Let me know what you think in the comments box.
Pros of Air-Cooled Grow Lights
Air-cooled grow lights remove some heat, but not the relative humidity
This, for me, is the biggest advantage using air cooled grow lights—but you only realize it if it's set up right. The cooling system for your air-cooled grow lights must be separate from your garden's ventilation system. The input air should be drawn from outside of your garden, not simply pulled through a carbon filter inside your garden or grow tent.
Setting up an air-cooled grow light the right way.
Watch our video on how to set up an air-cooled grow light for maximum efficiency.
Why? Well, it's all about control. if you're passing your garden's air through your hoods, then you're pulling humidity out of your garden too whenever you're cooling your lights (which is basically whenever they're switched on). Now—this might be a good thing or a bad thing. If you're growing in a basement in Florida you're probably glad of any opportunity to get rid of any moisture in the air. Phoenix, Arizona—the opposite problem. But the point isn't a matter of geography. It's about affording yourself the choice and giving yourself the tools to really take control of your indoor garden's environment.
Controling relative humidity is so important but it remains a bit of an enigma for many growers. If there's too much moisture in the air your plants can't breathe and the risk of molds and mildew skyrockets. If there's too little your plants over-transpire and eventually their stomata close and photosynthesis ceases, rendering your endeavors one big waste of time and energy.
As a side note, here's what I aim for in my indoor garden as a general guide for most species. Note the gradual decrease through the plant lifecycle.
Propagation: 80+% RH. Just rooted / early veg: 75% RH. Vegetative phase: 65% RH. Transition: 55% RH. Flowering 45-50% RH.
Air-cooled grow lights can be positioned closer to plants with less risk of burning or causing localized low humidity issues
Photons from the Sun travel 93 million miles to reach us here on Earth. That's over 491 billion feet. As such, the top of a plant growing in an outdoor patch enjoying full sunlight is arguably receiving the same amount of photonic energy as the bottom of the plant. (Think about it! An extra foot or two on top of that 491 billion isn't such a big deal!)
Indoors it's a completely different story. Grow lights are typically placed between one and three feet away from the plant canopy. The further you move away from the grow light, the less intense the light. Sure, this is true of the Sun too—you won't get much of a tan on Neptune. Even a few extra inches indoors can make all the difference. The true skill of lighting an indoor garden efficiently is to find what I call the 'sweet zone' - it's that perfect distance where your plants are receiving maximum intensity from the grow light without overheating because they're too close to the lamp itself.
Enter the air-cooled hood. You've probably heard the sales pitches—that cooling your HID grow lights removes up to 50% of the heat generated from the lamp—and this means you can lower your lights by three or four inches. This is great for plants that thrive in high light conditions but cooler temperatures (subtropics, high altitude) but remember that the footprint of your grow lights will be reduced too.
Air-cooled grow lights are great for Grow Tents and Enclosed Spaces
If you are growing light loving plants in an enclosed space then the age-old problem of getting sufficient photons to your plants while providing adequate ventilation and cooling is exacerbated. Air-cooled grow lights are a real boon for 'closet' growers or for those working in tight spaces showing there really is no need to compromize when it comes to getting that all-important energy to your plants!
You can use air-cooled grow lights to heat your home!
This tip is courtesy of Edward Bricker from our Facebook group. Sure you want that heat out of your grow room but why get rid of it during the cooler months of the year? Simply by redirecting some ducting you can channel that heat and put it to good use—keeping you and your family warm during the winter! You're paying for the energy so make the best use of it! Just make sure to channel it well away from your grow room.
Air-cooled grow lights afford growers more efficient use of supplemental carbon dioxide (CO2)
Similar to the first point about cooling without removing relative humidity, if you're beefing up the CO2 PPMs to 1100, 1200 or more, the last thing you want to be doing is venting out that precious carbon dioxide before your plants have had the chance to exploit it! Air-cooled grow lights allow you to remove the heat at source while leaving your garden's climate relatively undisturbed. Exact techniques differ depending on whether you are growing in a sealed indoor garden as opposed to a ventilated garden. Growers who ventilate their gardens tend to shut down their extraction fans while the supplemental carbon dioxide is being deployed—for ten to twenty minutes or more. They keep their oscillating fans running, of course, so that the extra carbon dioxide can be dispersed evenly around all their plants.
Cons of Air-Cooled Grow Lights
Air-Cooled Hoods Tend to be Big and Expensive
Sure—a quality, well-sealed air-cooled hood is always going to cost more to manufacture than your common 'batwing' reflector. These days they come in all shapes and sizes, from 4", 6", and 8" cool tubes (not big at all) to beasts like Sunlight Supply's Luxor and the OG. I guess the saving grace of air-cooled hoods is that you should only have to buy them once!
Cooling HID lamps can affect spectral output and intensity
High intensity discharge lamps create both light and heat. The light is generated as a result of large amounts of electricity flowing in an arc-tube and exciting particles. It could be said that the light-generating reaction needs heat so critics of air-cooled reflectors often claim that trying to cool this reaction is counterintuitive.
Does Air-Cooling Your Grow Lamp Reduce PAR Output / Light Intensity?
Check out this simple test using a Sun Systems PAR meter.
Air-Cooled Grow Lights Require More Maintenance
Let those glass panels get dusty and you could be losing 15 - 20% or more output! So air-cooled reflectors may not be the natural choice for lazy gardeners. The trick is to make regular maintenance a part of your plan. Growers don't get round to cleaning their reflectors because they tend to only be in their gardens when the lights are on—and then the last thing you want to be doing is unclipping hot glass panels and spraying window cleaner anywhere near a hot lamp! No, no, no. Weekly or monthly maintenance is a must. Pick your day, pick your time - just do it!
Air-Cooled Reflectors are a pain to adjust
Air-cooled grow lights require ducting, and lots of it, to vent all that hot air away and out of your garden. Now, we all know that ducting should be as straight as possible for maximum efficiency. (Bends and kinks in ducting causes noisy turbulence and reduced fan efficiency.) But this heuristic runs counter to another requirement—the ability to raise and lower your grow lights! Thus, it's essential that you allow some 'slack' in your ducting so that you can adjust your grow lights as your plants grow. My trick for this is to use some adhesive tape to consolidate / compact excess ducting.
The glass panel filters out ultra violet (UV) light
UV light is useful for stimulating the production of essential oils and for its natural antifungal / pesticidal effect. However, high pressure sodium (HPS) lamps do not emit any UV in the first place! Metal Halide (MH) lamps, on the other hand, do emit some UV—the higher kelvin lamps (10,000 - 20,000) produce more. For this reason some growers choose to use high kelvin metal halide lamps during the last week or ten days before harvest to increase essential oil production—particularly beneficial to crops such as basil and mint. Some growers using air-cooled hoods remove the glass panel
Vertically-mounted "Chinaman's Hat" Reflectors Can Be Placed Just As Close
One thing's for sure, mounting an HID lamp vertically dramatically decreases the amount of radiant heat directly beneath the lamp. When a lamp is mounted vertically, the tip of the lamp is the closest to the plant canopy and this generates far less heat than the long side of the lamp. Many growers, especially up in British Columbia, favor the vertically-mounted "Chinaman's Hat" reflector for this reason. It's possible to position the lamps very close to plants and let the heat rise naturally through the top of the reflector. Of course, chunky AC units are involved too in order to deal with the heat that inevitably escapes into the garden.
If you're a fan of vertically mounted lamps then why not get the best of both worlds and check out the Luxor reflector?
Okay—what did I miss?