I've actually not had a problem with it turning brown with too much light. I have a wrgb-2 which is far stronger than most aquarium lights and i float the hornworth. Furthermore the aquarium in question is a low tech (no co2
) aquarium; so I would question that 'too much' light causes it to turn brown. Now it might be darker green with lower light as many plants adjust their colour based on the amount of available light relative to their needs.