HID Lights - different sizes & prices

There are three major types of lighting systems available right now:

incandescent, fluorescent, and high intensity discharge.

Incandescent lights are horribly inefficient (especially the screw-in "grow bulb"
type) and really not an acceptable option for plant growth. Although they are
inexpensive to purchase, their cost of operation makes them the costliest
source of light.

Fluorescents:

Until the early 1980's most indoor growers used fluorescent lights to illuminate
their garden. These tubes have tremendous advantages over incandescents.
They emit about 3 times as much light as an incandescent (given the same
wattage), and the light spectrum is one that plants can use more effectively.
However, they do certainly have their limitations. Light is emitted over a large
area, so it is not concentrated. Because of this, the lights have to be hung
very close to the plants (usually about 1 foot from the plants), and constantly
moved to accommodate plant growth. This makes garden maintenance rather
difficult, even when the lamps are hung on chains. Florescents are, however,
very useful in cloning, and starting seedlings. Because in these stages, a plant
is not growing vertically very quickly, the disadvantages of moving the lights
are reduced. They also put out a more gentle light than the HID lamps, and
release less heat.

The fact that they produce less heat is very important to those growing in
enclosed and not-especially-well ventilated spaces. If you choose to use
fluorescents, it is best to purchase the 'coolwhite' variety. The ones that
are sold as grow lamps (including grow-lux, vitalite, etc.) are much less
efficient than a standard fluorescent, and just do not put out enough light
to be useful. The slightly different spectrum produced by these lamps does
nothing for most plants. Some growers have reported excellent results by
using a mixture of cool-white and warm-white lamps in a florescent fixture.

High Intensity Discharge Lamps (HID's)

High intensity discharge lamps are easier to use, and more efficient. Low
wattage HIDs are sometimes sold for household outdoor use. Large Wattage
lamps are used for lighting streets, parking lots, stadiums and other large
areas. They come in two basic flavors:

• METAL HALIDES or MH lamps emit a white light that looks slightly bluish.
  They are used to light stadiums, convention centers, gymnasiums, and
  other large areas where a natural looking light is desired.
  
  

• HIGH PRESSURE SODIUM (SON - T) or HPS lamps emit a pink or amber light.
  They are used for lighting parking lots and other areas where the color
  of the light is not important. HPS units are much more efficient than
  MH ones, producing more light and less heat per watt of energy consumed.
  They are often used alone with no detrimental effect on the plants,
  and will promote faster plant growth than MH lamps during both
  vegetative growth and flowering. Combinations of bulbs are not required,
  as the HPS lamp does produce all of the light spectrums necessary for
  healthy growth.
  
  

• There is also the SON-T-AGRO HPS bulb. Basically, the designers
  took a 400w HPS lamp, and added another 30W element to it, However, this
  new element puts out blue light, to help fill in the parts of the spectrum that
  a standard HPS is missing. I've never actually seen one of these bulbs,
  so I can't tell you about how efficient they are, but some Hydroponic growers
  think they're terriffic.
  

MH lamps are available in 175, 200, 400 and 1000 watt sizes. HPS lamps come
in 50, 75, 150, 400 and 1000 watt sizes. San Agro comes in 430w only, but
it works with a 400w HPS ballast. Each lamp requires its own ballast, which
comes with the fixtures that are designed to use these lamps, and are also
available separately.

The following chart shows how much light/lumens each lamp emits and the
area that it covers adequately:

Quantity of light

Light intensity is measured in Lumens (lm). During the flowering period, hemp functions
best at a high level of at least 40,000 lm per m2. Quantities of light exceeding 50,000
lm/m2 are a waste of energy. About 75 to 80% of the number of a bulb's lumens are
actually available. An example: An agro-bulb produces 52,000 lm. Actually, this means
0.8 x 52,000 = 44,000 lm. This means that one 400 Watt ballast produces enough light
for one m2.