Originally Posted by RobStark
I'm seeing some posts saying some LEDs aren't as good for deeper tanks as others. On a 21" tall 29 gallon bowfront, I might plant a few real plants in the tank eventually or have a few floaters. But for now just all fakes. Would you suggest the finnex ray 2 over the fugeray for this situation? Or would the marineland double bright LEDs do good enough?
This is true.
Each part of the visible light spectrum penetrates water depths differently. Red spectrum gets absorbed very quickly in terms of depth once it gets past the water surface. For the same light concentration, at the other extreme, deep blue spectrum is much more energetic and can penetrate to depths far beyond red. All the remaining visible colour spectrum in between varys in effective depth penetration between the two extremes.
fixtures for plant and coral growths have two main favours, (there is a whole range but it basically comes down to two main areas)
You can talk in terms of colour temps.
Like 3000 - 4000 degree K
fittings have a large red/yellow spectrum component. So their light appears yellowish to the eyes. These aren't so good for tank plants so not even a consideration for trying to light up a planted or coral tank. Ok if you don't mind the yellowish tinge and have a tank filled with fake plants or no plants.
Most commercial LED
fixtures are made for shallow(ish) tanks, these tend to have a large 6500+ degree K
component and in combination with some blue LEDs are great for the majority of tanks out to 12 - 16" depth.
Deep tank LED
fixtures are designed around 10,000 K
- 14,000K with greater number of blue and ultra blue LEDS. The greater concentration in the blue spectrum penetrates water depth much better and can photosynthesise plants and corals at the bottom. These give the tank a blueish tinge which (I think) looks pretty cool but the eye perceives it as 'less bright' even though the plants love it.
All this is given equal light concentrations between the examples. You can certainly pump more 6500'K
light into a 21" tank if you oversupply the light intensity to effectively get to the bottom. Brute force method to overcome the water depth loss.
Use google for some great information on light spectrum and depth penetration and effective light spectrum spreads for under water plant photosynthesis. Theres a whole science behind it all.