Waiting (im)patiently for payday to buy a proper light for my 20 gallon-high aquarium. Did some research on what bulbs/fixture to get and ran across this passage on a forum.
Makes sense to me.
Think about it this way – reef guys use actinics to simulate deepwater light wavelengths to stimulate coral growth in corals that tend to be deeper down in the water column.
Most aquatic plants grow in shallow lakes, rivers, and streams. There isn’t enough water to filter out the reds, so they are using full spectrum… when you get deeper down, plants disappear.. why do you think this is?