I feel similarly. When I have read articles/threads about what lighting a planted tank does best in it seems 1.5-2.5 watts per gallon is a recommended range. Also 6,500 degrees kelvin is optimum.
I would like to know more about optimum depth of a tank taking into consideration light dispersal. I have read deeper than 600mm is pushing it. But at which wpg ratio? If your tank is 600mm deep how many watts gives you successful light dispersal for plants which require medium-high light?
I read an old thread about Atman lights 10,000-15,000k which are typically used over marine tanks. If used over freshwater how efficient are these bulbs for plants growth seeing as they are such a high kelvin rating. Do the plants benefit from >7,000k or is it wasted on them seeing as they photosynthesize at 630nm, 700nm?
If you uses Gro-lux bulbs they lack the middles light spectrum which makes your tank appear dimly lit. Store clerks merely told me the listed lumens of a specific length bulb. The manufacturers website has the products listed, but there are hundreds of them - leading to more confusion than understanding.
Seeing as Phillips Cool Daylight 48" 36W tube is 6,500k and cost $4.90 from Mitre10 mega, why are the bulbs at LFS $40 odd?
Just pondering, would like to know. I don't mean to sound like I am complaining.