Lighting; PAR, Intensity, Spectrum, Feeding?

[Aquavadis]

Hi everyone,
I am fairly new to this forum and my first question is about lighting. I have read many articles about lighting but there are still many things that i am confused about.

These are my conclusions from my readings but i am not sure if they are correct:

-Lighting is important at the point of photosynthesis and there isn't a big difference in the ratings of photosynthesis of the corals under different spectrums -4000K-20000K- if light intensity is the same. But I think a spectrum under 5600K may cause algae growth. At this point intensity is more important than spectrum for coral growth and coloration.

- PAR is the other important characteristic of light for photosynthesis as well as light intensity.

- The bulbs having lower Kelvin temperatures have higher PAR values and provide higher light intensity than the ones having higher K degrees.
For example: 250 Watt 6500K IWASAKI has a PAR rating of 705 while 250W 10000K USHIO has 495 and XM 250W 20000K has 247.

- -If photosynthetical zooxanthellea provides %30-40 of the coral's nutrition -depending on the species- light musn't be the only factor affecting the coral growth and coloration. IMO feeding and water current are the other important factors. Because if we dont feed our corals we will not provide them the rest of their nutritional needs. This will cause lower coral growth and the overgrowth of brownish zooxanthellea so the more brownish look of the corals.

- Fluorescent bulbs provide a more uniform ilumination than MH bulbs but since the MH bulbs are point source they are more intense and provide a better light penetration than fluorescent bulbs within a span of 2 feet.

- I am not pretty sure about this but generaly 48" fluorescent bulbs have higher lumen/Watt values than the smaller sizes of the same type.

Here are my questions:

- Can we say that light intensity affects the penetration of the light and PAR affects the rating of photosynthesis?

- If a high quality 6500K MH bulb has PAR and intensity ratings twice as much as a 20000K MH bulb having the same wattage can we say roughly one 6500K MH bulb provides the intensity and PAR values provided by 2x 20000K MH bulbs having the same wattage and can we go with one 6500K bulb instead of two 20000K bulbs if it provides the PAR and intensity values that we are looking for?

- Since it is nearly impossible to find the Photosynthetic Photon Flux Density ratings of the bulbs can we simply use lumen/Watt ratings of the bulbs for having a general idea of light intensity of the bulbs? Is there any conversion formula for lumen/Watt to PPFD or any source showing the light intensity of different depths of tropical seas?

I have seen a Canadian made 40W 6500K fluorescent bulb having a light intensity of 3200 lumens i know that there some 4 footers having 3500 lumens. Roughly many of the 10000K 175 MH bulbs have a light intensity around 7000 lumens. Whenever we use 2x 4 footers having 3500 lumens we can get the same light intensity provided by a 175 W 10000K MH bulb. Yes MH's are more intense within 2 ' but we can use 3 or 4 40W fluorescent bulbs if we have enough space over the tank or we can keep the high light loving corals close to the surface. Kelvin temperature of the natural Sun light is around 5600K and many of the SPS corals especialy acroporas live close to the surface and the color temperature of the natural light musnt be that high in the shallow waters. So what makes 10K MH's superior than 6500K 40W fluorescent bulbs if we dont mind the color of light and dont have a space limitation in the hood?

- Isn't it possible too keep SPS corals under fluorescent bulbs if we keep them close to the surface, provide them enough light intensity, enough water current, and feed them regularly with phytoplanktoon and zooplankton?


I know i have asked too many questions i hope my questions won't bother you.

Thanks
Kadir

[AttackDonut]

That's a lot of research and questions.

Basically, PAR is important for the depth of the tank, and the MH for the power.

I've never seen anyone keep hard corals (for any length of time) under anything BUT MH lights.

I think the MH bulbs also have a wider spectrum than std. NO lights.

[fmuakkassa]

Good investigative work so far. I wish I did what you did BEFORE I set up my aquarium. (did not know about Reef Central). To make a long story short I recently bought an Apogee PAR meter and was shocked with the low PAR my two 150W MH were giving to the tank because I had them placed 2 feet above the water.

Distance is crucial and you never go wrong with getting powerful MH lamps. I see this is your first post. TAKE YOUR TIME and ask a lot of questions as I spent a lot of money on my light fixture and now I am thinking of changing it all again at a cost of $1500 to $2000 plus.

[Aquavadis]

Thanks guys for the replies.
I think i have to ask more questions before making a big investment But before i wanna know that if it is realy necessary to make a big investment on lighting. I am not telling that MHs or intense bulbs are not necessary but i still believe that there may be some cheaper solutions such as using high quality reflectors, feeding, locating light loving corals close to the surface, arranging rock work not to shade and scatter the the light, using more intense low K bulbs, going with a shallower tank etc. I believe there are too many other factors affecting coral growth and coloration else than lighting.Also there are many factors affecting the quality of lighting as well.

Here is a link to Scott Morell's 120 G SPS tank under 7x40W NO bulbs.

http://www.garf.org/ScottNewLook/OldLookFront640.JPG

Despite that he switched to VHO bulbs later for me the tank looks good and the corals look healthy under NO bulbs.

Thanks
Kadir

[Rikko]

You can absolutely grow SPS and even tridacnids under NO fluorescent tubes. I've seen it done, but they need to be extremely close to the water surface.
That said, I wouldn't suggest it. There are so many more tasty and fun ways of lighting.

You put it well saying that light intensity affects penetration, though I'd say that you can simply call PAR how "much" light there is.

Honestly, forget about the Kelvin thing. It's pointless and you'll get nowhere. Ever seen,say, 6400K bulbs from different manufacturers? They look nothing alike. Hagen's Power Glo and Aqua Glo 18,000K bulbs are actually something like 8000K and 7000K. It's used too loosely as a marketing term for many makers.
You can very roughly say that 6400-6700K is about white, lower than that gets yellow/red, and above that starts to go blue. I've got some full spectrum 6400K T5 tubes that have a spectral graph showing almost a level bar across the entire visible spectrum - if that's true, that bulb is producing a helluva lot more light than any bulb that looks a little brighter but isn't "full" spectrum. If nothing else it sure made my algae go nuts (FW).

I find lumens are the best way to compare bulbs. Watts are a hopelessly useless figure and any measure of intensity is too obscure for mainstream aquarists. And if my product data I have here is right, yes - you get more lumens/watt with longer tubes.

At the end of the day you really just need to consider a couple basic things:
1) Everything you're going to keep in your tank is likely accustomed to living at least 10 feet below the ocean surface.
2) Your tank is really quite shallow comparatively.
Which lets you deduce:
3) The blue shifting of the light spectra that you get at depth needs to be artifically stimulated in your tank if you want to replicate reef conditions. And that's really why actinics are popular.

You might find this article interesting:
http://www.advancedaquarist.com/issu...03/feature.htm
They ran a test using a few different LEDs over a coral. The red LED caused bleaching. The blue LED caused red colouration (which is natural for that species).

You already know more about lighting and photosynthesis than the majority of reefkeepers in the world, and probably more than a lot of aquarists at public aquariums. Don't stop, but don't get bogged down either!

[Aquavadis]

Woow that was a good article . Thanks for the info and advice.