We investigate the difference air-cooling your lamps makes to their output using a PAR meter (quantum meter).
As growers, we already know that our high intensity discharge (HID) grow lamps housed in air-cooled reflectors can safely be positioned closer to plants without causing heat-stress, localized low humidity stress, or burning. It's their big selling point. With every inch you can safely get your lights closer to your plants comes exponentially increased light intensity and deeper canopy penetration, meaning lower parts of the plants receive the photons they need too.
Of course, when it comes to designing your indoor garden and working out your lighting requirements, you need to note that positioning your lights closer to your plant canopy will also result in a smaller footprint (the area you cover with your grow light) so you may end up needing more lights to cover the same area (but you'll be doing it with greater intensity!)
There's another factor to consider too. Passing cool air over your grow lamps will affect their operation slightly. Metal halide and high pressure sodium grow lamps, by their very nature, need to run hot. Passing cool air over your lamps reduces the output a little—around 6 - 8 percent depending on the temperature of the air you're using to cool your lamps.
Does Air-Cooling Your Grow Lamp Reduce PAR Output / Light Intensity?
We use a PAR (quantum) meter to compare the light intensity at 24" away from a 1000W Ultra Sun Metal Halide lamp with and without air-cooling.
However, as the video above shows—PAR levels are way higher when the reflector is lowered just a few inches—something that's perfectly safe and feasible to do when air-cooling your lamp.
My conclusion? Air-cooled reflectors are not for everybody. But if you are growing light loving plants from sub-tropical, higher altitude regions then they could really help you achieve the high light intensities required for optimum growth and bloom while keeping temperatures moderate enough to promote the production of important essential oils and aromas.
Also, air-cooled lights allow you to deal with the inherent heat problem caused by grow lights at source. You can vent up to half of the heat away completely independently of your garden's ventilation system meaning you don't have to strip your garden of valuable relative humidity as a side-effect of removing the heat.
I recommend air-cooled reflectors most strongly to growers using grow tents, in confined spaces, or those interested in cultivating sub-tropical species native to higher altitudes.