Summer can present a real challenge for indoor gardeners. When things heat up outdoors it can cause temperatures to soar in your indoor garden unless you are properly prepared. High temperatures bring with them a whole host of problems. Your plants go into “survive-mode” rather than “thrive-mode.” That means that they stop focusing on growth and bloom and instead turn all their energies to “getting through it” – whether you are growing fruit, vegetables or herbs the result is the same: lower yields and lower quality. Downer! There’s also an increased risk of pests in hot (and dry) environments, and woe betide you if you allow your nutrient solution to become too warm – you may as well send a personal invitation for Miss Pythium to pay all your plants a visit! It’s no surprise then that many growers decide to close down for a few months and turn their attention to outdoor crops, but it’s still perfectly feasible to keep your indoor garden going 365 days a year with no disruptions, no matter what climate you live in.

The obvious heat-beating tactic is to install an air-conditioning system. But this just isn’t feasible or desirable for everyone. Other growers use air-cooled lighting to manage rising temperatures in their indoor gardens. After all, it’s your HID bulbs that generate the vast majority of heat – so it makes sense to tackle the problem at source.

Air-cooled lighting is not a complicated idea. The bulb is encased behind glass in a tube or reflector. Both styles have two holes at either side, one for air to be blown in and one for air to exit, taking heat with it. So, using an extractor and a few lengths of ducting, it’s pretty simple to create a stream of cool air, blown directly over the bulb, which constantly cools it. The hot air exiting the reflector is then ducted out of your indoor garden, minimizing its potential to heat up your growing environment.

Suck or Blow?

For best results, the cool air should be blown over the bulb, not sucked over it. There’s still a lot of debate in the indoor gardening community over this one – but one good reason is this: it’s better for the fan to blow cooler air through it, rather than “suck” hot air straight into it from around the lamp. You can also align two or three air-cooled lights in series using one fan and ducting in between lights – this technique is popular with growers using larger fans and reducers. It also makes for a lot less ducting and fan chaos! The cooler the air you can pass over your HID bulbs, the more heat it is able to remove. A properly air cooled light can remove up to 50% of the heat of the lamp. Some growers even go to the extent of passing air-conditioner-cooled air over their lamps (and not air-conditioning their indoor garden itself!).

However, air-cooled lighting isn’t just something that’s nice to have in the summer months – it allows you to position your lights closer to your plants all year round, meaning they can enjoy a greater light intensity. And more light on your plants = more yield. It’s as simple as that. Air-cooled lighting also reduces the cost of running a large air-conditioner. A cooler bulb results in less bulb stress and failures. It is much easier to remove heat at the source rather than try to get it after it has entered the indoor garden. Due to the small volume of air in the reflector (compared with the entire volume of the indoor garden), much less energy and effort is required to remove the same amount of heat.

As mentioned earlier, there are two types of air-cooled lights available: tubes and reflectors. Cool-tubes allow the grower to extract heat from the bulb completely without having to deal with the resistance of a larger, potentially more cumbersome reflector. However, the spread of light from a cool tube is smaller. Rectangular air-cooled reflectors usually come with a flip open glass lid beneath the lamp.

Some early air-cooled reflectors used low quality glass. Big mistake! The lower the quality glass, the more it absorbs light – light that your plants could be using. Make sure your air-cooled rig uses top quality glass. But even more importantly – KEEP IT CLEAN! Dirty, dusty glass can absorb more than 15% of the light from your lamps instead of it reaching your plants. Also remember: glass absorbs UV which can help with the production of essential oils in some crops (e.g. mint, basil and rosemary).

When ducting air from your air-cooled lights, make sure you use insulated ducting inside your indoor garden. This will help to prevent heat escaping through the ducting itself and thereby increase the efficiency of your cooling.

Finally, check how well sealed your air-cooled reflector is. An easy way to verify this is to switch on the fans that are cooling your reflector (and no other fans in the room) and light a match underneath it. Blow it out and watch the smoke. Does it get sucked up towards the reflector? Bad seal! Good seals are particularly important when you’re adding additional CO2 to your indoor garden as you don’t want it to be extracted through your lights before your plants have benefited.

Other bits and bobs you may need:

• Insulated ducting to match reflector and fan – 4″, 6″, 8″
• Duct clamps – 4″, 6″, 8″
• Inline fan
• Timer for fan (or fan could be plugged into the same timer used for light)

New Innovations: The Ice Box

Instead of ducting the hot air out of your indoor garden, check out “The Ice Box” by Hydro Innovations – it’s a specially designed heat-exchanger that fits on the exit-flange of your 6” air-cooled reflector. Using water at just 65 °F (18 °C), the manufacturers claim that it can remove all the heat from a 1000 watt lamp! Pretty damned impressive, and no ducting overload in your indoor garden!