If I my be permitted to correct a couple of things in past posts...
First, the situation in an aquarium with plants is different from those plants in their respective habitat. If you look at the videos of habitats in the Amazon basin for example, you will not see what most aquarists would consider "healthy" plants; they are usually spindling and algae-covered. Most of the plants are amphibious, spending half the year emersed and half submersed, and it is during the emersed period that they reproduce and grow most. The conditions we aim to provide in an aquarium have to be well thought out because we are providing far more ideal conditions in the water, but with that comes the problems like algae, oxygen/CO2 imbalance, light much too strong for fish, etc. None of this occurs in nature because the water courses that have plants (most do not) have fewer fish or the fish have refuge from all that light.
As for spectrum, as the graph posted in another post shows, aquatic plants require red and blue light to drive photosynthesis. Red is the more important, but blue is needed too. And while green light plays no part in photosynthesis, scientifically-controlled studies have proven that high green light improves the plants' response. Diana Walstad opinioned this was probably due to the additional intensity the green provides to the red and blue, and that natural sunlight is high in red, blue and green and the plants have evolved under this light, so naturally they will make the best use of it. Diana also notes that light having a colour temperature in the 5000K to 7000K range provides the best light for aquatic plants because it is high in the red, blue and green.
Many LED lighting units are too high in the blue; this is because they are largely aimed at marine tanks; blue light is prevalent in the ocean because it penetrates water much more effectively than red, so corals need strong blue light. Things are much different in freshwater. And too much blue does cause algae issues.
