Hi niru,
The paranoia regarding solar spectrum is a direct result of a couple of key misunderstandings which have themselves become myths:
Here is misunderstanding #1 which has turned into myth #1:
"Aquarium tubes have spectral energy distribution that peaks in frequencies which are most beneficial for plant growth."
The fact is that all visible wavelengths (from 400nm to 700nm) are most beneficial to plants. These wavelengths are also most beneficial to algae. Plants and algae share pretty much exactly the same mechanisms for photon assimilation. The mechanisms are pigments. The most well known of these pigments are called Chlorophyll. There are a couple of different varieties of Chlorophyll, but generally these are mostly sensitive to blue and red wavelengths. However, there is still plenty of useful energy in wavelengths other than blue and red, so plants have other pigments that are sensitive to the yellow, green, and orange wavelengths.
Not all environments are open Savannah illuminated with full solar spectrum. Many environments are shaded and filtered. Imagine a plant growing in the shade under a canopy of tall trees. The color of the light reaching the plant will be mostly yellow/green as it passes through the leaves of the tree. In an environment such as this the plants will have a higher percentage of pigments that are sensitive to yellow/green in order to maximize efficiency. They might also have a higher density of Chlorophyll in the leaf to squeeze as much energy from the available light as possible. In comparison, a plant growing in an unshaded open waterway will actually be in danger of energy overload so it will have a high density of pigments that actually reflect the blues, reds, and UV.
Plants therefore must have the ability to assess their environment from a spectral standpoint in order to determine what density and distribution of types of pigments to allocate to the leaves to prevent overload and at the same time to maximize energy usage. As a result, any spectrum that you provide to a plant will immediately be analyzed, and the plant will respond to that spectrum by developing and allocating the necessary pigments.
So if you use only high intensity blue bulbs, the plant will determine that pigments sensitive to blue are needed but that a low density of these pigments are required and perhaps even that some pigments which reflect the blue to avoid overload. There are even pigments which can actually convert the blue to another color. if you decide to use red bulbs then the plant will perform an analysis and allocate pigments that maximize the use of red while avoiding overload. Any type of bulb that you use will be analyzed and responded to.
Here is misunderstanding #2 which has turned into myth #2
"...opportunistic algae should also make use of this! To extend further, perhaps they also use of IR or other heat "radiation" that plants might not be using..."
Plants are descended from algae. It was bacteria and then algae who figured out how to use solar radiation. They passed this knowledge on to higher plants. Therefore, whatever light is good for plants is also good for algae and whatever wavelengths are useful to algae are also useful to plants.
There is a biological equation however that results in a higher demand for nutrients/CO2 with increasing intensity. The difference is that plants require thousands of times more nutrient/CO2 than algae do. Therefore, under high spectral loading the plant will exhaust it's ability to uptake sufficient levels of nutrients/CO2. because of their much greater complexity and much greater mass, they need more nutrition and are less efficient at getting that nutrition, even if it's available. Plants therefore suffer easily under high lighting, but algae thrive under high lighting. Conversely, plants can survive under low lighting whereas algae suffer dreadfully under low lighting. That's why blackouts work against algae. Algae need more light because they have low energy reserves.
It's ironic that the first thing people think about when deciding to get into planted tanks is the idea of getting super sexy high lighting, and it's actually the last thing that the plants need, but it's just what the doctor ordered for algae.
The reason you tend to get BGA on the front of the tank is simply that there is the most ambient light at the front, combined with poor flow to the substrate. Try putting some black tape across the front for a few weeks and see how quickly it disappears. The BGA is telling you that you need to pay more attention to flow distribution to the substrate as well as that you possibly might need a bit more NO3 dosing.
Cheers,
