6500 k lighting

do your corals grow faster with a 6500 than a 10000 k

Depends on who you ask :)

Edited by m.ash - September 01 2011 at 1:09pm

Aquaristnewbie wrote: From what I ahve heard 6500K will give you great growth but make your corals look like crap at the same time and like stated above, it will let nuisance algae thrive. From my experience something around 14K gives you the best of both worlds with good growth and good color. I used to use 20Ks and loved the color I got from those and also liked the blue tinit it gave my tank

The corals looking like crap comes from the fact that a 6500K bulb or even a 10000K bulb doesn't have very much light in the UV spectrum that causes corals to grow the beautiful neon colored zooxanthelae that protect them from UV light.  Leaving corals under low temperature bulbs will let them grow, but they won't look very impressive color-wise.  14000K is a nice medium between the extreme of a full blue at 20000K and a very white 10000K.  The neon bright colors that you see in corals come from them protecting themselves from the UV light, it is like a natural sun block, but if you don't have that spectrum, you won't have the pretty colors.

I agree with Ryan that corals do better and thus have their best color when the water is just how they like it both is composition and movement. But lighting does have an important role.
 
The answer to the original question is not cut and dry. Some coral will grow better in lower Kelvin light, like bright sunlight, especially those coral that naturally grow in the surf and down to 20 feet. The coral we grow in our tanks come from depths of 5-100 feet or more. All those coral will not do so well in bright sunlight because some of that light spectrum (like red) actually inhibits growth in deeper dwelling coral. We assume that zooxanthellae are genetically inclined to grow best at specific wavelegths of light which approximate the wavelengths of light they receive at their ideal depths. See the pics below for a revealing look at light in the ocean.

From what I have seen and learned in the last 20 years, MH bulbs for the aquarium hobby were developed from low Kelvin value bulb technology (5000-10000K). The technology had developed some very powerful yellow-white lights. Though the color we saw in those bulbs was yellow-white, the amount of blue wavelength light in those bulbs was also very intense. This meant that those bulbs were found to grow coral very well because they also put out intense blue light.

In recent years the technology for aquarium MH bulbs has greatly improved. The manufacturers have developed intensely powerful bluish white and blue (12000-20000K) MH bulbs. So now we find coral growing just as fast under those lights as it used to grow under the old 6500-10000K MH lights. Add to that the addition of intense illumination from fluorescent lights developed for the hobby with the bluer spectrum in mind and we now find coral growing faster than ever before.

Most of the color we see in coral is reflected light. The color of the coral is dependent on whatever light wavelengths are shining on the coral The lower the Kelvin value the yellower the light source and the more of the color of the coral is simple reflected light and thus not real interesting.

Coral absorb some wavelengths of light and in turn emit light in wavelengths that vary slightly from what was shined upon them.  Most but not all of this reflected or emitted color comes from the zooxanthellae algae, but it would be misleading to say that it's all due to the algae, because without the coral, the algae wouldn't survive for long and vice versa.






Thank you Jacques Cousteau.




Edited by Mark Peterson - September 01 2011 at 6:35pm