THE TRUTH ABOUT WATT RATINGS
When purchasing a compact fluorescent, you will notice that nearly all of them have a larger number on the box, than what it actually is. This number is the lights comparison to the brightness of a standard incandescent globe. Do not be fooled, this does not mean that the light is 100w! It is most likely around 18w.
Now, here is where the myth behind these lights is uncovered. Most people will say that you should totally discard the brightness rating. This is wrong! The brighter a light is, the more penetration it has. With a usual, run-of-the-mill compact fluorescent (say, 15w) it emits only 15w of light with poor penetration. An energy saving compact fluorescent with 15w of light, which is rated to 100w of light, will only emit 15w of light. The difference between the two is, the energy saving light has a much stronger light penetration of the normal one, while still only emitting 15w of light.
This is beneficial to growers because with a larger plant, a normal 15w compact fluoro will sufficiently light one part of the plant, and by the time the light has reached the other side of the plant, so much of the light has been lost that it is barely worth having. With the energy saving compact fluorescents, the light will travel to the other side of the plant, and still have enough intensity for reasonable results.
