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The Nuances of HID Light Reflectors

August 17, 2016

What’s so special about HID reflectors? Aren’t they just there to hold the lamp and help direct more light to the plant? Well, yes. They do those things, but they can also be much more valuable if you understand the nuances of how they work, and choose the right reflectors to increase your harvest.

The first thing to understand is that although high pressure sodium bulbs can be operated in any position, standard metal halide (MH) bulbs should be operated vertically to prevent dimming the bulb and shortening its life span. To accomplish this, MH bulbs use a vertical light fixture and reflector. But specialized horizontal and universal MH bulbs can be operated in a horizontal light fixture with the accompanying reflector.

There are many different types of reflectors on the market today. These include fixed, adjustable, super wide, parabolic dome and air-cooled types. Each type has its advantages and disadvantages, and some don’t work well for cultivating cannabis.

So, why should you be concerned with the type of HID reflector you use? Although some types reflect more light than others, some shapes reflect light more evenly. Even distribution of light eliminates hot spots, so bulbs can be positioned much closer to the tops of the plants without burning them. For instance, a 1,000 watt HID bulb with a reflector that creates a hot spot must be positioned at least 36 inches away, but a 600 watt bulb with a reflector that distributes light evenly can be placed 18 inches above the plants. As a result, the plants receive just as much light from the 600 watt bulb as from the 1,000 watt bulb. In fact, the proper reflector combined with reflective walls can double the effective size of the growing area.

Material and design affect efficiency

The type of reflector material is also important. Reflector hoods are commonly made from either cold-rolled steel, pre-galvanized steel or aluminum. Aluminum reflectors dissipate heat significantly faster than steel reflectors do. Although they cost a bit more, they’re worth the extra expense because the bulbs can be placed closer to the plants.

A reflective surface of metal—polished or mirrored, pebbled or hammered, or with a white powder coating—is usually applied inside the reflector.

  • Polished metal and mirrored surfaces are best avoided. Polished metal reflects less light than white surfaces, while mirrored surfaces scratch easily and tend to create hot spots.
  • Pebbled or hammered surfaces provide more reflective surface area and better light diffusion.
  • While the white-powder coating is the most common type and works well, some shades of white are better at reflecting light than others. Gloss white is easy to clean, but flat white reflects more light and distributes it more evenly. Flat titanium white reflects the most light of all coating types.

Other reflector types

Additional types include glass-enclosed and wing reflectors. Although glass-enclosed hoods are good at focusing light into a highly defined area, they can cause heat to build up inside the enclosure and shorten the life of the bulb. These hoods are usually air-cooled but they may produce fewer lumens. That’s because the light must pass through the glass either before or after reaching the reflector. Wing reflectors distribute light more evenly than all other types; they are also the coolest.


By Bill Bernhardt
Cannabis Cultivation Today articles are for informational purposes only and should not be considered legal guidance or advice on grow practices. You should contact an attorney or a qualified cultivation consultant for specific compliance and cultivation advice.




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