Which is the best reflective hood for HID lights?

Reflective Hood Study, Excerpted from Chapter Two, Indoor Marijuana Horticulture, The Indoor Bible

Reflective Hood Study

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 and black. The floor was covered with black tar paper. Less than three percent light could be reflected from the black surfaces. There is 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 had to use five different lamps in tests, a 1,000-watt clear super metal halide, a 1,000-watt HP sodium, a 600-watt HP sodium, a 400-watt super metal halide and a 400-watt HP sodium. The measurement to the floor was made from the bottom of the bulb and exactly three feet from the floor. Every lamp 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. Some reflectors focus all the light in the center of the room and leave little for the perimeter. Other reflectors are very inefficient.

The studies show a huge difference between reflective hoods. Some of the companies developing the hoods do not test them 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 making your tests, take your readings at the same locations. Measuring two or three points is OK to test a bulb for lumen maintenance.

When light distribution is even, the lamp can be placed closer to plants. The “Light and Distance Chart” shows that light diminishes very quickly. It shows that 3 feet from the bulb there is only 1/9th as much light as 1 foot away! This evidence means that sun-loving marijuana grows best when a reflector that spreads the bright light in a large pattern over the garden and get the lamp as close as possible to the garden.

In general, the larger the wattage of the bulb, the more efficient it is. However, since light intensity diminishes so quickly, bulbs must be close to plants. This means that more lamps or point sources of light are necessary for even distribution of bright light.

Operating costs for three 600-watt HP sodiums are lower than to run two 1000-watt HP sodiums. The 600-watt sodiums 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 the atmosphere. Excessive heat around the bulb causes premature burnout.

Super Size Secret: For maximum reflection, paint the inside of the reflector with titanium white paint. Titanium white reflectors produce 5 – 10 percent more light.

Light Reflector Studies

This page of light studies shows the distribution of several types of light reflectors. The graphs clearly show horizontal reflectors deliver many more lumens than vertical setups.

Technical Stuff: Check out the “Light Measurement Handbook” available free on the Internet. The 64-page technical book answers endless light questions. Download the book in a few minutes, photos and all: www.Intl-Light.com/handbook/.