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Old 09-03-2008, 10:11 AM   #1
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Talking Just A Basic Lighting Question

Which option is the better choice?

option 1.> A 15watt bulb with 10,000k
option 2.> A 40watt bulb with 6,500k

Which is more important, the wattage or the kelvin rating?
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Old 09-03-2008, 10:24 AM   #2
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Honestly I don't think this is answerable without any background information. Kelvin is just the color temperature or spectral distribution and wattage is implies intensity of energy. If this question were initially relating to reef tanks housing corals then photoadaptation for photosynthesis would be in question of which PAR (light in range of photosynthesis) would be of more importance; however, your question could relate to a small fish-only tank, refugium, etc...
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Old 09-03-2008, 10:36 AM   #3
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So, would it be a fair statement to say this. "A 15w/10,000k bulb would give off more of the full light spectrum than a 40w/6,500k bulb" ?

Also, I'm trying to keep this question as simple as possible. So, please try to keep the technical answers to a minimum. With that said, this question is not related to any kind of partiular tank. So, if you could, when answering this question, just give me the run down of what factors to look for in a bulb for each application (FO, FOWLR or Reef).

If you need a scenario or some specific information, let me know what information is needed to make a determination.
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Old 09-03-2008, 04:11 PM   #4
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Also, what is the best brand of lights to purchase? Does anyone have any favorites and if so, why?
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Old 09-03-2008, 05:13 PM   #5
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In general full light spectrum (lower K ratings like 6500) promote more growth in plants and algea. There are going to be more yellow and white light. Higher K rated bulbs (10,000 - 20,000k) are going to be much more blue and will be much better for corals. How many watts is a seperate issue from the Kelvin rating. People keep all differnt kinds and combinations of lights and its a very debated topic so you will probably get a lot of different answers to that question on which kelvin rating you should have for differnt kinds of tanks.

I wouldn't worry about the best brand yet. You first have to decide what kind of lighting. for example PC (power compact) or T5's or MH (metal halide). all of them have ups and downs for differnt kinds of tanks. I would try to figure this out and then come back and ask people about brands and fixtures.

I can tell you from when i was trying to figure all this lighting stuff out that it will be much easier and you will get better answers if you can first figure out what kind of tank you would like to keep and what kind of corals if it is a reef. Once you tell people that you will get much more informed responces and suggestions. otherwise if you just looking for a general overlay of lighting i would just google search it and its not hard to find some good articles which will be more detailed.
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Old 09-03-2008, 05:25 PM   #6
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thanks for that answer. it was a great help, but i will provide more details and see if i can find out more information that way like you suggested. okay, so here it is:

90g tank
regular hood and lights (standard 2 bulb lid)
Fish/Live Rock/Star Polyps and other hardy (beginners corals)
1" sand bed
wet/dry filter (with live rock instead of bio balls)
inline heater
salinity within normal range
temp within 74 and 78 degrees

with that said, i am thinking about replacing the bulbs in my standard lid with a (40w 420 Actinic blue) and a (40w 6,500K - 20,000K). with those details, can my question be answered better now?
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Old 09-03-2008, 05:33 PM   #7
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Yes that helps quite a bit. With a tank that size 80W of total light really is barly enough to keep even low light corals. If you want to keep a range of easy soft corals and polyps i would suggest looking at T5 fixtures. Try to aim for 2-4 watts per gallon. Corals absorb and use blue spectrum light the best. I would probably suggest going half and half actinic blue and 10k lights.

When looking at T5 fixtures make sure you do a little research on the reflectors. A reflector for each bulb and parabolic shaped reflectors are the best.

Lighting is not cheap so make sure you do your research on what kind of corals you want to keep and the appropriate lighting for them. Buying a quality fixture that is well researched will save you a lot of issues and money down the road.
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Old 09-03-2008, 05:36 PM   #8
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It is standard practice that you need at least 3 - 4 watts per gallon. Even at the low end of 3w per gallon only works out to a total of 270 which isnt much. It is sufficient for just fish but if you dabble into corals, you will need more. This standard canopy that you are talking about only has room for two fluorescent bulbs correct?
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Old 09-03-2008, 05:39 PM   #9
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Quote:
Originally Posted by thekeyofb View Post
So, would it be a fair statement to say this. "A 15w/10,000k bulb would give off more of the full light spectrum than a 40w/6,500k bulb" ?
No, not at all. "Full light spectrum" is a variable,depending upon the light source. For example, the spectrum of an incandescent bulb is markedly different from that of a metal halide. The peak output of a light source is indicated by the Kelvin temperature of the source. A higher Kelvin temperature is "bluer" than a lower Kelvin temperature, which tends to be more yellow or red. Just for reference, the sun emits at 6,500K, measured at the top of the atmosphere.

For terrestrial growth, professionals tend to use higher Kelvin temperatures for initial growth, while using lower temperature sources for flowering; so, the "correct" temperature not only varies by plant, but by growth phase.

It's not often a good idea to emulate the solar 6,500K with your aquatic lighting. Our eyes are adapted to increased sensitivity to "warmer" parts of the spectrum (reds/yellows), and a 6,500K output will appear "unnaturally" blue to the eye. Ironically, a "cooler" (i.e., bluer) light may be better for plant growth. The reason for this is that the reds and yellows are absorbed by water more quickly than blues. So, a lamp with a higher blue output (e.g., 10,000K) will deliver more light to the plants in deeper water. For the same reason, aquatic plants have evolved to use those colors for photosynthesis to a greater degree than their terrestrial counterparts.

I use a fixture that employs SunPaq bulbs (Current USA fixture). Part of the bulb delivers 10,000K radiation, while part of it concentrates its output at 4,600 Angstroms, which corresponds to a blue-violet color.
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Old 09-03-2008, 05:44 PM   #10
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The short answer is 2 40w normal oputput fluorescent bulbs is probably not enough light in a 90g tank for any coral unless it's at the top of the tank, and you will be limited to only soft coral.

As far as your bulbs, an actinic has very low PAR (Photosynthetically Active Radiation). It's not of much use to coral, it's more for eye candy. I'm assuming the other bulb is a type of 50/50 (actinic/full spectrum) bulb. Generally they have more PAR are thus are better for all around coral growth/health.

74 to too cold. Stay between 76-80.
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