Here's a basic introduction to the various types of air-cooled grow light reflectors and some practical tips plus pros and cons!
Firstly, you need to know three important things about grow lights and plants:
1) HID grow lights create a lot of heat as well as light.
2) Plants rely on light energy in order to grow and bloom-a process known as photosynthesis. BUT ... and this is such an important but ... this light must be supplied in an environment at the right temperature. If plants are subject to excessive heat they will "shut down" rendering all your lighting efforts largely redundant.
3) For every inch you position your grow light closer, your plants receive exponentially more incident energy from the lamp, but that inevitably brings more heat too!
As you can see, we have a potential conflict on our hands-or, to put it in a more positive way, a compromise to be sought. We want to give our plants as much light as possible - so the closer the better (3) but too close (2) and they stop developing due to excessive heat! (1) Remember, every inch counts when it comes to indoor horticultural lighting. If you halve the distance between your lamp and your plants, they receive around four times the light energy! This is nothing like growing under the Sun!
So-how do we resolve this tricky conundrum? Enter stage left: air-cooled reflectors! They give growers some valuable leeway when it comes to safe distances between the canopy of your plants and the lamp. In short, you can get your grow lights closer, without raising temperatures beyond those ideal for photosynthesis and other key metabolic plant processes. The result is more dynamic growth and deeper light penetration into the main body of the plant.
How do Air-Cooled Reflectors work?
The primary job of an air-cooled reflector is the same as a regular (non air-cooled) reflector: to focus the direction of light emitted from the lamp so that as much of it as possible hits your plants.
Air-cooled reflectors come in three main styles but they are all based on the same simple principle-to use a continuous flow of air to keep the lamp and reflector cooler. Obviously, as the air passes over the hot HID lamp it heats up. This warm air is then ducted directly out of your indoor garden-helping to keep temperatures cooler and your lights closer to your plants.
All air-cooled reflectors have two circular ports-one for receiving air and one for exiting air. Growers use an inline fan to blow cool air into the input port and ducting to whisk the warm air away and out of the grow room.
Be sure to take note of the size of these ports-most commonly they are 6", 8" and 10" in diameter. (There are even some 4" models around for those dinky-style Europeans!) Obviously you will need to spec your fan and ducting accordingly.
A Brief History of Air-Cooled Reflectors
The very first models appeared in the early 1990s. They were not very efficient at reducing grow room temperatures because they were not sealed, built from a loose sheet of tempered glass that slid into guides added to the bottom of existing closed-end reflectors.
Also, early designs were based on 4-inch diameter ducts utilizing standard dryer hose. Generally speaking, these duct adaptors were not integrated into reflector design, but were add-on devices that you could bolt to the ends of your reflector.
The first design to fully incorporate ducts on to the sides of the reflector was the original Super Sun reflector by Sunlight Supply. Major advancements include integrated duct adaptors, larger duct diameters, sealed glass systems, hinged sealed glass systems, and built-in aerodynamic socket assemblies that direct airflow more efficiently over the lamp.
Three Air-Cooled Reflector Designs
The illustrations below show how cool air flows over the lamp, absorbs some of the heat energy, and is channeled away. Air flow is created using inline fans and ducting (NOT shown)
Cool tubes are the most slim-line and minimalist of the air cooled fixture designs. The lamp is housed within a glass cylinder (either 6" or 8" diameter)-some have a small reflector built in to beam the light down and others have no reflector (for vertical grows where plants are positioned at 360 degrees around the lamp and lit from the side, rather than from above) Cool tubes are ideal for confined spaces and lower wattage lamps (250W to 600W.)
This is the most common style of air-cooled reflector. The lamp is housed horizontally inside a metallic housing with a removable glass panel beneath the lamp. Common sizes are 6", 8" and 10" for input and exiting air. Some designs have a single 'exit' port at the top of the hood, rather than one either side. Two ports (one for input air, and one for exit air) affords the grower more control over whether the cooling air is drawn from-especially useful if you are growing in a CO2 enriched environment. Look out for quick-release clamps on the glass panel and good, tight seals for optimum cooling efficiency.
A relative newcomer to the market-the HID lamp is mounted vertically inside a large, reflective housing with a glass panel below. This design seeks to exploit the fact that there is less radiant heat directly below a vertically-mounted HID lamp than a horizontally-mounted lamp. The heat that does escape is drawn upwards into the venting chamber.
Air-Cooled Reflectors: Dos and Don'ts
- Use insulated ducting to vent the hot air away. This will dramatically increase the efficiency of your cooling. In the winter months many growers redirect exhausted heat into living areas of their homes, saving on overall household energy costs.
- Keep your ducting as straight as possible with minimal bends.
- Use the coolest air you can for the cooling! Duh! Using garden-temperature air will have little effect. Take an input from a cool room or a vent in a shady wall instead.
- Measure the temperature at the canopy of your plants using an infra-red thermometer. The ideal temperature for optimal photosynthesis for more plant species is around 75 to 79 °F (25 to 26 °C) in a non CO2 supplemented environment (slightly higher - around 82 °F / 28 °C) with CO2 enrichment up to 1350 PPM)
- Remember that bringing grow lights closer to your plant reduces its footprint (light spread) so be sure to measure light levels at the margins of your grow room to ensure they are adequate.
- Connect more than two lights in series. You are better off bringing in a wide 12" duct (aka "trunk") of cool air and using 'T' pieces and reducers to split off separate cool air inputs into each reflector.
- Forget that your indoor garden will become depleted of CO2 levels as your plants grow. You will still need to use A/C and supplement CO2 levels or ventilate your garden's air too.