Here is some insider information that should help!
(this is an exert from the section on lighting in my book)
Light Intensity
Light intensity diminishes the further it has to travel. This is the same for HID, CFL or your normal household lamp.
If you hold a light meter up close to any lamp and then slowly lower the meter, even a few inches, you will see the light measurement reduces dramatically.
(If you can borrow, beg, steal or get access to a light meter please try this ~ you will be extremely surprised at the rate at which the light intensity reduces over a short distance)
Light from an HID or HPS lamp reduces by half for every foot it is away from the plants.
So if your lamps are 2 or 3 above your plants much of the light is wasted. The problem with HID lamps is they are so hot you cannot place them close to your plants and much of the light, and your money, is wasted.
One benefit of using high-out put CFLs is that they do not generate as much heat and can be kept almost on top of the plants producing the exact 100% PAR light, with no loss of intensity.
(So if you position these new lamps close to the leaves you get the benefit of 100% PAR light in the correct 400nw to 700nw range, giving the plant the correct light colors and light quality.)
Growing With CFLs
CFLs can be used to grow seeds and to propagate cuttings.
They can also be used as the main lighting system for plants in the vegetative and flowering stages.
(The secret to growing with CFLs is to position your lamp or reflector just an inch or two above your plants.)
Positioning these new compact lights directly above the plants maintains light intensity, no lumens are lost and the PAR / Spectrum is 100%, which is like natural sunlight.
The plants get all the lumens they need with the light being in the correct spectrum.
CFLs are available in 125w and 200w models that are avaible in:
> Natural Daylight 6400k (kelvin) (Great for vegetative growth)
> Warm (Red) 2700k (kelvin) (Great for FLowering)
Many growers use these lamps as a supplement to hang by the side or in between plants when flowering.
They can be used with HPS lamps, as a supplement or by themselves.
We use them 100% and no longer use HPS lamps.
Some red light in the vegetative light mix is also recommended, as is a little white / blue light in the flowering mix.
With different combinations of red and white lamps growers can obtain the ideal lumen output and spectrum required for excellent results in all stages of growing.
125w and 200w CFLs provide 100% PAR, which is such an important factor.
It is important to be able to calculate the PAR values obtained from your grow lights and how much light your plants need to give maximum yield.
If you are using HID / HPS lamps you should contact your supplier and ask them about PAR output, it is important that you know this as well as lumen output.