by Jorge Cervantes
Reflective Hoods
Use an efficient horizontal reflective hood to direct the most light from a bulb toward plants. A good reflective hood provides 10-40 percent more light than an inefficient one. The ideal reflector can be placed close to the garden canopy and will distribute light evenly.
A reflective hood that distributes light evenly – with no bright hot spots – can be placed closer to plants without burning them. When the lamp is closer, the light plants receive is more intense. In addition to reflective walls, the proper reflective hood over the lamp can double the growing area.
Reflective hoods are made from steel sheet metal, aluminum, or even stainless steel. Some hood manufacturers apply (Titanium) white paint in a powder-coating process. The pebble and hammer tone surfaces offer good light diffusion and more surface area to reflect light. Hot spots are commonplace among highly polished, mirror-like surfaces. Mirror-polished hoods also scratch easily and create uneven lighting.
Horizontal reflectors direct half the light downward toward plants, requiring only half of the light to be reflected. Selecting an efficient reflective hod will increase the efficiency of your lamp.
Vertical reflective hods with vertical lamps are less efficient than horizontal ones. Reflected light travels farther before being reflected in parabolic or cone-shaped reflective hoods.
Lightweight reflective hoods with pen ends or sides dissipate heat quickly. Extra air flows directly through the hood and around the bulb in open-ended fixtures to cool the bulb and the fixture. Aluminum dissipates heat more quickly than steel. Train a fan on reflective hoods to speed heat loss.
The closer you put the reflector to the bulb, the more intense the light it reflects. Enclosed hoods with a glass shield covering the bulb operate at higher temperatures. The glass shield is a barrier between plants and the hot bulb. Enclosed hoods must have enough vents; otherwise, heat buildup in the fixtures causes bulbs to burn out prematurely. Water-cooled and air-cooled lamp fixtures are somewhat popular in hot climates. These lamps run cooler and can be moved closer to plants.
Using no reflective hood is an option. With no reflector, the lamps burns cooler and emits only direct light, The lamps must be suspended between plants to be used most efficiently.