Marine hobbyists use light combinations that contain blue spectrum to help the kind of high microorganism growth needed to help feed corals and inverts. I find an easy way to think about it is that coral reefs are usually along the ocean edges in warm areas with lots of bright sunshine beating down and nothing to get in the way and cause shade. Part of what makes the daytime sun so dazzling in these places is the high blue content in the total spectrum of light (or some describe it as a very clean white quality, rather than dazzling.) This encourages algae and bacteria in extreme amounts and its the base food for these ecosystems.
In contrast to this, the Amazonian and African and central american lakes, streams and rivers where many of our tropical freshwater fish come from can have a very different light. The rivers and particularly the streams can have overhanging plants on the banks and trees overhead. The water may have lots of green plant leaves or floating plants adding shade. There is the potential for a very different, green sort of light (from all the reflections of leaves and stems) but of course its still the sun. Additionally, the geography of the land can be a factor, with mountains and hills casting shadows for part or much of the day.
Straightforward daylight tubes work quite well in freshwater aquariums, no need for special plant lights either. Note that tube color discussions can be found in the planted tank section archives.
~~waterdrop~~
Theres a Q i need answering though - it has (what i believe to be) a UV light - is this bad for plants/fish, as the only light source (apart from daylight)?? Do i need to change the bulb?
(sometimes in the US you can catch a glimpse of the real stuff in reruns of the old Rockford Files tv shows 
I hhave posted in the diy section about lamp recommendations, and would love some input 
