by Nebula Haze
When growing cannabis under HID grow lights like MH or HPS, you want to take as much light from the bulb as possible and deliver it directly to your plants. This is important because maintaining strong light levels in the flowering stage is the only way to grow dense buds and get brag-worthy yields. Higher light levels (up to a point) are also associated with increased potency.
By using a reflector (especially when combined with reflective walls), you can get a significant amount of extra light to your plants without using any more electricity, resulting in faster growth and bigger harvests.
The hood / reflector focuses light down, increasing light levels experienced by the plants
But which reflector is best for your grow light and space? Is it worth it for you to get a better or more expensive reflector than what you have now, or will your results end up being about the same?
Let's break it down!
Always Get an Air-Cooled Hood
There are three main types of hoods/reflectors: wing reflectors, cooltubes, and air-cooled hoods. Each of these types will reflect light down onto your plants, but they differ in how well they reflect the light, and how well they contain the heat of the bulb.
In order to get the highest levels of light to your plants you need to be able to keep your grow lights close, but that can be impossible when the heat from a naked bulb is beaming directly down onto your grow space like with a wing reflector.
Wing Reflector (sometimes called a "bat wing") – Cheapest type of reflector, be careful of sharp edges! Wing reflectors are usually pretty good at reflecting light, but they can make it difficult to prevent heat from beaming down on your plants. Even if you have a fan blowing directly over the bulb you may not be able to keep bulb close enough for maximum light efficiency. Not recommended.
An air-cooled hood is a must to contain the heat from your MH/HPS bulb so you can safely bring your light close to your plants. The heat gets contained behind glass, and the hood itself can be easily hooked up to a fan to vent extra hot air outside the grow space.
If you take a bulb from a wing reflector and put that same bulb in an enclosed air-cooled hood, the overall temperature in the grow space will likely stay about the same (since the bulb is still giving off about the same amount of heat), but the temperature felt by your plants in the top canopy will be dramatically less since the heat is being enclosed near the bulb instead of beaming down. That means you often will be able to keep a bulb much closer if it's in an air-cooled hood compared to a wing reflector, increasing light levels without causing extra heat stress to your plants.
Air-Cooled Hood – considered the "golden standard" of reflectors, they contain heat away from your plants by trapping it behind a piece of glass located at the bottom of the hood. They have holes in the side so they can easily be hooked up to an exhaust fan via ducting. Air-cooled hoods are the most effective type of reflector when it comes to reflecting light downwards while also keeping plants cool. They are even good at containing heat when not hooked up to an exhaust (though venting out the extra heat will certainly give you the best results). Highly recommended!
Cool Tube – A Cooltube is a variation of an air-cooled reflector that takes up less room so it can still contain heat but will fit in smaller spaces. Although these are great for cooling, they usually have a smaller (less effective) reflector than either a batwing or a full-sized hood. Only recommended if you can't fit a full sized air-cooled hood in your grow space!
Summary: Why get an air-cooled hood?
- Most effective type of hood for reflecting light down to your plants
- Prevent heat stress by containing heat near the bulb (also giving you overall greater environmental control)
- You are able to keep lights closer to plants for increased light levels using the same bulb/electricity
- Can be easily hooked up to an exhaust system or a carbon filter via ducting
- Ideal for grow tents as they have been specifically designed to work together to help growers create the perfect indoor growing environment
Get the Most Effective Hood for Your Light & Space – Narrow vs Wide Dispersion of Light
When growing cannabis in a tent or other restricted space, you want to get a hood that's been specifically designed to get the most amount of light to your plants in a space like yours with the bulb you have.
Hoods either reflect light straight down or they disperse light in a wider area, and each type of hood can be a good option depending on your goals.
Hoods and reflectors that are more narrow/tall with straight edges tend to beam light down more directly, which means plants will experience a higher intensity of light (and increased penetration below the canopy), but in a smaller area. This can be helpful if you're growing with big grow lights that must be kept further away from your plants, or if you're growing in a tall space and want deep penetration.
Tall, narrow hoods with straight edges tend to beam light directly down, providing deeper penetration but also reducing the light footprint
On the flip side, hoods that are wide and short with angled sides tend to disperse light over a wider area. It's helpful to get a hood that disperses light if you want to maximize the area that receives light (create a bigger light footprint, though light is less focused). A hood that disperses light over a bigger area can also be kept closer to your plants as long as heat is under control, thus increasing light levels without reducing the light footprint up to a point. This can help create strong, even light levels over your entire grow space even with a smaller sized light like a 250W or 400W HPS.
Hoods that are relatively short and wide with angled sides disperse light over a wide area
Get a tall, narrow hood with straight edges if…
- You want to get deeper penetration below the canopy
- You want a high level of light in a focused area
- You plan on keeping lights relatively high above the plants
Get a short, wide hood with angled edges if…
- You want more even spread of light coverage
- You want to cover a larger area with your grow light
- You want to be able to bring your light closer without sacrificing footprint (great for increasing light levels with some of the smaller HPS sizes without increasing electricity usage)
Although there are specific cases where a more narrow hood might be more effective, I personally believe most hobbyist growers would be better off with a wider hood, as it lets you give plants higher light levels by moving lights closer, without reducing the amount of space you can use to grow plants. However, wider hoods often cost more than narrow hoods so if price is an issue, that may be a consideration.
A few last tips…
Get Most Reflective Hood as Possible (95% Reflectivity)
Hoods commonly come labeled as having 85% or 95% reflectivity (though some may not say anything about reflectivity, which usually means it's 85%). Although it's often more expensive to purchase a hood with higher reflectivity, it's not a bad idea if you can afford it! Although there's not a huge difference in performance between the two types, the 95% reflective hoods definitely do reflect more light. Every bit of extra light received by your plants can make a difference!
A Good Hood Can Be Opened Up
This may be something you don't think about the first time you're getting a hood/reflector, but they each have different ways to get inside so you can screw in your bulb.
If possible, get a hood that's been labeled as having either "hinges" or "sliding glass" (preferably hinged) in order to get to the light socket. Otherwise you might be sticking your hands in from the side air hole whenever you want to change the bulb. Not being able to get past the glass can also make it difficult to clean the inside of your hood if it gets dirty (and the glass should be as clean as possible to make sure it's not blocking any light from getting through). However, although this is a matter of convenience for you, it doesn't really have much effect on your plants.
Do I want a 6-inch or 8-inch opening on the sides?
Every air-cooled hood has an opening that can be used to connect the hood to a fan or ducting. These openings come in different sizes, so which do you choose? 6-inch is the most common size, and has the most options, but you may have reasons to want a bigger size.
6-inch – Effective for cooling up to three lights that are hooked together <— Most common sieze, if you're not sure, get this!
8-inch – Necessary to get enough airflow when more than three lights are being hooked together, though you have fewer options
Make sure your hood has the right sized openings for the ducting you plan to use (if in doubt, get one with 6-inch openings)
In this section I'm only going to recommend air-cooled reflectors (no wings!) as they deliver the best results for cannabis growers.
"Narrow" Hood ($70)
I used this hood for a few months and it is great for containing heat and pointing light directly downwards, but the steep sides give it a somewhat narrow footprint that prevents you from being able to bring the light close without reducing the amount of space you can use to grow plants. At 12" it can cover about a 2'x2.5' area. At 18" it can cover a 3'x3', and at 24" it covers a 4'x4'.
"Cool Tube" Hood ($50)
This Cool Tube hood is perfect for growers who want an air-cooled reflector but don't have the space to put a bigger hood in their garden (though if you can fit something bigger you should probably go with that for the better reflector).
The dimensions of this Cool Tube are 23" x 6" which means it should even be able to fit even in a small closet or grow box as long as you have enough space lengthwise. The wing reflector can be removed if you need to make it fit in an even smaller space.
"Wide" Hood ($70)
This hood has a great light spread which allows you to bring the hood closer to the plants without reducing the footprint. At 12" away it covers about a 3'x3' footprint, at 18" it has a 4'x4' footprint, and at 24" it has a 5'x5' footprint. Yet despite its wide spread it is small enough to fit in most setups (since the spread is helped by angled sides). Dimensions are 22" x 20" which means it will even fit in a 2'x4' grow tent with room for ducting, though a tight fit! I'm using this hood now in a 3'x3' tent and I'm very happy with it.
Brand Name "Wide" Hood ($170)
This hood has a lot of really great features, though it comes with a big pricetag. This is the 3rd generation version of this brand name model, and it has been specifically designed for even light distribution in square spaces. This hood has 95% reflectivity, and the angles of the reflective materials have been engineered so the hood doesn't create hot spots and disperses light most evenly. The dimensions are 25 1/2" x 25 1/2" which means it can't fit in any space that has a 2' width or less, so it's not good for smaller setups. At a foot away it covers about a 3'x3' footprint, at 18" it has a 4'x4' footprint, and at 24" it has a 5'x5' footprint. There is also an 8-inch version. If I was going to pick a new hood and money wasn't an issue, this is the one I would get 🙂
Now that you know a little bit more about different types of hoods and reflectors, are you ready to set up your light and start growing? Learn how easy it is to set up your MH or HPS grow light!