For a grow in a small area I don't see how HID lights are more effective and are stronger light sources. Assuming I use 400 watts (real watts) of cfl light I will get over 25,000 lumens. Now is I use a 400 watts MH I will get 36,000 lumens and 55,000 watts from a HPS. Now here is where I think cfls should get the advantage. Light intensity decreases greatly as the distance from the plant is increased. With cfls, I can put the lights right up 2 inches from the plant. This keeps the light intensity pretty close to the original lumen output. With the HIDs I would have to keep the light about 1 to 1 1/2 feet from the plant. I believe this would cut the lumen intensity in half if not even more. I can also get color specific clfs to concentrate for veg and budding just like MH and HPS lamps. So why would HID lamps be so much better than cfls?
Without getting to much into the math and science of light, I will try to explain to the best of my ability why CFLs aren't as effective as HIDs.
First of all, HIDs are obviously more effecient than CFLs (Let's take 3 typical examples):
23w CFL = ~1800 initial lumens = 78.3 lumens per watt
400w MH = ~36000 initial lumens = 90 lumens per watt
400w HPS = ~55000 initial lumens = 137.5 lumens per watt
So for the same wattage you'll get less lumens and more overall heat with multiple CFLs than you would with an HID light. Not to mention, with CFLs you must contend with the heat from the ballasts, whereas with HID lighting you have the option of mounting the ballast outside of the growroom.
Most people associate CFLs with LESS heat because they don't use 400w worth of them. You would have to mount 17 x 23w CFLs in your growroom just to match a 400w HPS, watt for watt, that's not even taking lumens into consideration. If you had to match lumen output of 23w CFLs to a single 400w HPS, you'd need ~30 x 23w CFLs. Now that would be quite a bit of heat to have to remove from a grow, just to get the same amount of light as a 400w HPS.
Now on to light intensity. I won't get into the detailed math with this parameter because it gets into fairly complex physics that gets really boring, so I'll explain it the best way I can. HIDs are called High Intesity Discharge for a reason. The light output is from a single source point which is intense, whereas a single CFL emits considerably less lumens and spreads those lumens over a spiral approx. 12 inches long if unwound. That being said, light, just like gravity is governed by the inverse square law which states that light output is reduced by 1/4 for every doubling of distance from the source. You may initally think that you LOOSE valuable lumens by increasing the distance from the bulb, but you must take into account that when you double the distance from the bulb, you reduce your lumens by 1/4, but the light is spread over 4 times the area.
For example:
400w HPS:
Light output at 6" is 40000 lumens, illuminated over 1 sq. foot
Light output at 12" is 10000 lumens, illuminated over 4 sq. feet
Light output at 24" is 2500 lumens, illuminated over 16 sq. feet
23w CFL:
Light output at 2" is 1600 lumens, illuminated over 6 sq. inches
Light output at 4" is 400 lumens, illuminated over 2 sq. feet
Light output at 8" is 100 lumens, illuminated over 8 sq. feet
DISCLAIMER*** These are basically just abitrary numbers to demonstrate the inverse square law and may not reflect the real numbers you would get if tested in a lab!
So as you can see by the above example, you aren't "loosing" lumens per se, you are just spreading them over a larger area.
So to answer your original question, why not use CFLs instead of HIDs when you can mount them mere inches from the plant without harm?
Sure, you can do this, but that 1600 or whatever lumens your getting is spread over a tiny area, you'll need several of them just to cover one plant. Whereas, an HID you can mount a foot away and get 10,000 lumens over a 4 sq. ft area.
So when you do the math, CFLs just don't match the light output over the same area as an HID does, no matter how close are how far away the light is. Also with a more intense single source point of light, the light is more efficient at penetrating the canopy. It's sort of like electricity. The higher the voltage for a given wire guage, the less resistance there is to the flow of electrons. As with light, the higher the lumens from a given point source of light, the lower the resistance the light encounters through foliage, etc. Does that make sense?
Sorry about the long winded reply, but I'm tired of hearing people who claim that LEDs or CFLs are better than HIDs (not refering to you). They're not, at least not at the present time. I'm open to new technology, and one day HIDs will be replaced by something even better, but until that day, HIDs are king. Now for those people that just want to grow a couple grams in a PC case, CFLs fit the bill perfectly, but for those that have ample space and are growing to maximize their yeild, nothing touches HIDs.
