Additional Info
Given that we're no longer using soil, the plants need access to nutrients which are supplied in the water. Nutrient solutions typically contain a broad range of elements in a concentrated form. The following is a list of you would expect to find in most products.
Nitrogen (N), Potassium (K), Phosphorus (P), Calcium (Ca), Magnesium (Mg), Sulphur (S), Iron (Fe), Manganese (Mn), Copper (Cu), Zinc (Zn), Molybdate (Mo), Boron (B), Chlorine (Cl)
Different plants fare better or worse depending on the nutrient concentration and pH, so monitoring the nutrient levels and choosing plants appropriately will be necessary. A great environment for one plant may be less advantageous to others.
Over time the pH of the nutrient solution in the reservoir will change. From our experience, it typically tends toward becoming more acidic. Here is an explanation of what is occurring. It is a product of the nutrients in the water breaking down the water into hydrogen and hydroxide ions. Depending on the ratio of ions formed, it will tend more acidic or basic. There are additional processes whereby the plants deposit salts back into the solution, contributing to the change in pH.
Chlorophyll absorbs light most effectively in two narrow bands of the light spectrum. Specifically, at ~430nm (blue) and ~670nm (red) wavelengths. These frequencies are about 30nm lower than the blue of RGB and 30nm higher than the red of RGB. This difference is enough to make RGB lighting completely inappropriate for our purposes. The lights in the hydroponic rig contain a combination of LEDs engineered to emit specifically at the 430nm and 670nm frequencies where plants absorb most effectively.
Here is a fantastic paper by NASA outlining an experiment testing the efficacy and efficiency of growing plants with different light spectra.
Additionally, there are certain plants which contain a mutation of chlorophyll known as Chlorophyll B. These plants contain both Chlorophyll A and B with B representing about 20% of the total chlorophyll cells. Varigated plants - typically identifiable by their spotted leaves - have developed this mutation to assist in living in lower light conditions of the undergrowth.