Reflective Hood Study

I constructed a black room, everything black inside, to measure the amount of light reflective

Plants grow in vertical slabs and are irrigated from above in this recirculating garden.

hoods yield. The room was 10 x 10-foot square (3 rtv). 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 (30 cm) on a matrix marked on the floor. The walls had one-foot increments marked.

I tested five different lamps: a tOOO-watt clear super metal halide, a 1000-watt HP sodium, a 600-watt HP sodium, a 400-watt super metal htilide, and a 400-watt HP sodium. I positioned the bulb 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 (30 cm) 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 ! did here to find out which reflector is the best for your needs.

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

In general, the larger the wattage of the bulb,

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A. Spuculcir - Mylar and mirror give the best Strength of fight, but it is concentratcd. About 90% of the light is transferred.

f). Diffuse • Equivalent to a non-shiny matte surface. C. Spread - licit white surface that is diffuse with reasonable spread.

Reflective Chart



Reflective Mylar Flat white paint Semi-gloss white Flat yellow Aluminum foil Black

How to add light without using more electricity.

Any unused light is wasted. There are several ways to gat the mast out of your light without adding more watts, including:

Use several 400 or 600-watt lamps instead ol 1000's. Manually rotate plants regularly. Add a shelf. Install rolling beds. Grow a perpetual crop. Use a light mover.


Mow small plants to shelves around the perimeter of the growroom. Remember, plants grow wherever light shines!

the more efficient it is. Since light intensity diminishes so quickly, bulbs must be close to plants. Consequently, more lamps or 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-walt 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 the atmosphere. Excessive heat around the bulb causes premature burnout.

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

Check out the "Light Measurement Handbook" available free 011 the Internet. The 64-page technical book answers endless light questions. Download the book in a few minutes, photos and all:,

Continue reading here: Reflective Light

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