[RichardDean]

I posted it before but I will post it again since some people don't seem to know the correlation between the 2 spectrums of blue and red they go hand in hand.

Light Spectrum.
The average color temperature of the sun is 5800 Kelvin throughout the year. What we see on earth has barely measurable spectrum differences between spring and fall.


The sun produces energy in pulses, like a carrier wave. Let us consider the photosynthetically active portion of this pulse, from the lowest frequency--red (675 nm)--to the highest frequency--blue (400 nm). (“nm” means “nanometer”. A lightwave that is one nanometer is one billionth of a meter in length.)


This pulse is like a train, with the blue in front and the red in the rear. The Red light acts like an engine placed at the end of the train, pushing the orange, causing a chain reaction, the whole spectrum working together synergistically. The best light for plant growth is full spectrum, like the sun, with a slight increase in red spectrum due to evolution and the fact that red travels through forest canopy better than blue.


Red light is the most efficient monochromatic spectrum for plant growth. However, all the colors have functions. If a person were especially good at hearing bass sound, that means the other pitches should be emphasized, so that one could hear the whole melody. For light to be efficient for plant growth, it must be full spectrum with close to equal linearity and amplitude through the production of 400-700 nm, with a slight bump in the red.


The blue spectrum has the highest energy and shortest wavelength [see: Light Measurement Handbook (1997), by Alex Ryer, page 8].




Blue is in the front of the light train, acting like a spearhead to penetrate the leaf, carrying the other colors with it. The far blue range includes UV-B, similar to what is found at high altitudes, and increases the prized phenolic compounds. This increases the flavor of peppermint, licorice, pepper, etc.
Conventional wisdom dictates that the growth phase be illuminated by a quartz metal halide (for blue light), the bloom phase by a high pressure sodium (for yellow/
orange light). However, a full spectrum is needed for all phases for a variety of functions. Blue induces growth hormones and rooting, and reduces stem elongation. Red induces flowering hormones, and provides energy for growth of flowers and leaves. Using only quartz halide during growth phase results in slow growth due to less red light. Using only HPS light during flowering stage often causes leaf yellowing, due to lack of growth hormones; and tends to cause stem elongation.


An artificial light which reproduces a red-enhanced full spectrum is the “Ceramic Metal Halide” or “High Pressure Metal Halide”. This has more blue than a metal halide with a conventional quartz arc tube, and more red than an HPS, so it’s spectrum is optimum for all stages. The Ceramic Metal Halide (CMH) features a ceramic arc tube like an HPS, and uses an HPS magnetic ballast. Philips has recently come out with a horizontal version of this bulb, resulting in longer bulb life and 1000 lumens more compared to a vertical cmh bulb operating horizontally. Generally, horizontal works best.


For those limited to magnetic ballasts, CMH is probably the best plant light available. For the Life Light electronic ballast, Life Lights also produces full-spectrum pulse-start metal halide bulbs. These are more efficient than normal halides, with better spectrum. They are designed to accommodate the 100,000 pulse rate of the Life Light electronic ballast. These come in four spectrums:
*6K for rooting and early veg
*4K for general growth/bloom
*3K for late bloom
*10K for finishing (last 2 weeks)
If you can’t afford all four bulbs, the 4K is fine for all stages.


The CMH has a better spectrum and is more efficient electrically than the retro-fit HPS that operates on a MH ballast. The retro-HPS is more expensive, lasts only half as long, and has reduced output, compared to a regular HPS.