[GpsFrontier]

My question is this....if plants only absorb certain spectrums of light such as red and blue (blue for growth and red for bloom) why don't we just use these colors like with LEDs ?

Actually plants absorb more than just blue and red, they actually absorb every color in the rainbow. Think of it in shades, there's a multitude of different shades of blue in the rainbow, same as with red. Orange shades are important to plants as well, but are really only different shades of red (mixing of red and green light produces shades of yellow, orange). Red and Blue are two primary colors, but depending on how they are mixed with green can make every color in the rainbow.

But it isn't actually colors that plants are absorbing, the plants are actually absorbing wavelengths of radiation (energy). The radiation/energy is what fuels the process of photosynthesis in plants. Each color of the rainbow is a different wavelength of energy, colors are just a perception by the human eye. That's why when you use a MH bulb that's in the blue spectrum, you don't actually see blue light, and it doesn't make everything look blue. The blue is the wavelength of energy given off by the bulb.

The reason that you see the blues and reds so deeply in led's is because they focus on a narrow band of this spectrum. Each LED bulb can only give off one wavelength of energy, unlike a bulb that can give off thousands of wavelengths. There was a simple experiment done on a show called "Head rush" (my the people who do Myth busters). They took 3 light tubes (glow sticks), one of each primary color (red, green, and blue), attached them to the spokes of a bicycle wheel. Then posed the question what color will you see when they spin the wheel and the colors all blur together. The actual color you see is white. It's not a coincidence that's the color you see from a MH bulb. All the colors (wavelength of energy) are mixed together. It is no coincidence that is the color of light you see given of by the sun (that contains all the colors in the rainbow perceived by the human eye), and contains each and every wavelength of energy/radiation.

Primary color - Wikipedia, the free encyclopedia (scroll down to "Biological basis")

My real question is if red and blue leds grow plants as well as what I have been reading, then why wouldn't red and blue cfls work.

I'm not sure what it is you have been reading, but if it's what the LED light manufactures are writing, and calling it scientific data, you may want to take another look. I call that propaganda, and it's all written to try to sell products, and isn't objective information. Although there is no doubt that LED's use less electricity, I haven't seen any objective study's that suggest that LED's are even close to the capability's of MH and hps yet. I have seen that for some specific plants, and depending on the number of LED's, and how they are set up can grow some plants well. But nothing in comparison to what using MH and HPS can accomplish.

As for using Blue and Red colored cfl bulbs. As I said in answer to the first question it isn't about the color visible to the human eye ,it's about the wavelength of radiation/energy given off from the bulb. So you cant just color the bulb blue or red and expect it to work. But CFL's do come in blue and red spectrum's, but just like MH bulbs they contain all the other wavelength's also, so they look white to the human eye.

It has been a while but if I remember correctly the lower "K" numbers are the red spectrum (like 2700K), and the higher "K" like 6500K are the blue. Color and Mood : ENERGY STAR. Here they mention that the lower numbers are more yellow to the human eye, But remember that yellow is shade of red (made from red and green primary colors). So the lower the number, the more in the red spectrum the bulb is. When talking blue and red spectrum's, they are not saying that they don't contain other wavelengths (colors,) just that they focus more in one area than another.

A top of the line led light is in the ball park of. $2500, 13 watt. Colored. Cfl is $5

As for the cfl, colored glass in a cfl bulb is only going to block the energy/radiation from reaching your plants, just the same way putting on sun glasses blocks the suns energy/radiation from reaching your eyes. As for LED's being expensive, besides the fact that it's a relatively new technology being used in hydroponics, there's a difference in the LED bulb. The LED's used for growing plants are a high output (high intensity) LED bulb, and can run as much as $5 or more for just one LED bulb. Depending on the LED light fixture, it may have 40-50 of them, to hundreds and hundreds of them. But the light intensity from even these High intensity LED's are no match whatsoever to the light intensity of MH and HPS. Besides the light intensity, LED's are very limited in the range/spectrum of energy (wavelength) they put out, and again are no match for the MH and HPS.

From what I have been reading leds have less lumens than cfls, and the reason that they work so well is by targeting the red and blue spectrum of light in theory a red and blue cfl should work as well or better than leds right?

You can try using colored cfl's bulbs, but I can pretty well guarantee you wont have any luck. But if they do by some chance grow plants, you would still be better off using the same output bulbs, but without the colored glass. Again it isn't about the color of visible light to the human eye, it's all about the wavelength of energy/radiation given off by the bulb, and the intensity of it that reaches the plants canopy (foliage/leaves) that maters.