Reflective Hood Study

Marijuana Horticulture

by Jorge Cervantes

I constructed a black room, everything black inside, to measure the amount of light reflective hoods yield. The room was 10 x 10 foot square. The floor was covered with black tar paper. Less than three percent light could be reflected from the black surfaces – there was no extra light in this room. Measurements were made every 12 inches on a matrix marked on the floor. The walls had one-foot increments marked.

I tested five different amps; a 1000-watt clear super metal halide, a 1000-watt HP sodium, a 600-watt HP sodium, a 400-watt super metal halide, and a 400-watt HP sodium. I positioned the bulb exactly three feet from the floor. Every amp was warmed up for 15 minutes before taking measurements.

The foot-candle readings on the floor were taken every 12 inches and the results posted to a spreadsheet program. I used a simple spreadsheet graph program to present the graphic results.

The studies show a huge difference between reflective hoods. Some companies do not test their hoods before putting them on the market. To protect yourself and your plants, set up tests like the ones I did here to find out which reflector is the best for your needs.

When a reflector distributes light evenly, the amp can be placed closer to plants.

In general, the larger the wattage of the bulb, the more efficient it is. Since light intensity diminishes so quickly, bulbs must be close to plants. Consequently, more lamps r point sources of light are necessary for even distribution of bright light.

Operating costs for three 600-watt HPS lamps are lower than for two 1000-watt HPS lamps. The 600-watt lamps produce more lumens for the same amount of money, plus they can be closer to plants. There are also three point sources of light, which evens out distribution.

A heat vent outlet around the bulb helps dissipate heat into atmosphere. Excessive heat around the bulb causes premature burnout.