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Old 07-31-2010, 05:54 PM   #1
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MH lighting question

I just bought a clamp on 150w medal halide for my reef tank. I have that running with two actinic blue 39w T5 HO bulbs. My halide lets off a very blueish light. I know that halides are supposed to let out a lot more red light. I did see something about the light being blue but I cant remember. What's that all about?
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Old 07-31-2010, 07:05 PM   #2
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Red? I've never heard of MH bulbs letting off red light. The color variations all depend on the type of bulb you buy, and what Kelvin rating they are.

10000k - Yellowish
12000k - Yellowish/White
14000k - Crisp White with a hint of blue
15000k - Still pretty crisp white but with more blue
20000k - Very blue(However, some of the more high-end bulbs have a nicer tint of blue than the normal deep blue)

Those are really the only types of colors i've seen for halide bulbs. If your light is giving off a blue color, then it's more than likely a 20000k bulb. Could be a 15000k bulb.. but my guess is 20k.
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Old 07-31-2010, 09:33 PM   #3
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i have never seen visible red light from reef compatible halide lamps.
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Old 07-31-2010, 10:10 PM   #4
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Sorry when I said red I was talking about the color spectrum, I ment more reds and yellows then blues and greens. But your Kelvin expination explains it perfectly. It's actually a 14000k and does have quite a blue tint. Now does this do the same as actinic light. My problem is the support on the top of the tank, goes right through the middle as most do. With the light mounted in the middle I get a huge shadow in the middle all the way down. Should I get rid of the T5 and get another clamp MH? It's a 46 gal bow front reef tank. With two separate MH lights I can get rid of the shadow, but doubt I could fit the 36" two bulb T5.
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Old 07-31-2010, 11:12 PM   #5
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Well our SUN is in the 5000 - 6000k range with up to 6700k considered sunlight.
10k is very white with the blues starting in at 14k and 20k considered blue.

Actinic is in te 50k range (near violet/ ultra violet).

But that's only part of the story. You also have to consider the full spectrum output of a bulb, not just it's peak output. That is measured in nano meters (03 Actinic is 420 nm)...

Light Spectrum in NM
Violet Light
The visible violet light has a wavelength of about 400 nm. Within the visible wavelength spectrum, violet and blue wavelengths are scattered more efficiently than other wavelengths. The sky looks blue, not violet, because our eyes are more sensitive to blue light (the sun also emits more energy as blue light than as violet).
Indigo Light
The visible indigo light has a wavelength of about 445 nm.
Blue Light
The visible blue light has a wavelength of about 475 nm. Because the blue wavelengths are shorter in the visible spectrum, they are scattered more efficiently by the molecules in the atmosphere. This causes the sky to appear blue.
Green Light
The visible green light has a wavelength of about 510 nm. Grass, for example, appears green because all of the colors in the visible part of the spectrum are absorbed into the leaves of the grass except green. Green is reflected, therefore grass appears green.
Yellow Light
The visible yellow light has a wavelength of about 570 nm. Low-pressure sodium lamps, like those used in some parking lots, emit a yellow (wavelength 589 nm) light.
Orange Light
The visible orange light has a wavelength of about 590 nm.
Red Light
The visible red light has a wavelength of about 650 nm. At sunrise and sunset, red or orange colors are present because the wavelengths associated with these colors are less efficiently scattered by the atmosphere than the shorter wavelength colors (e.g., blue and purple). A large amount of blue and violet light has been removed as a result of scattering and the longwave colors, such as red and orange, are more readily seen.

Color Wavelength (nm) Frequency (THz)
Red 780 - 622 384 - 482
Orange 622 - 597 482 - 503
Yellow 597 - 577 503 - 520
Green 577 - 492 520 - 610
Blue 492 - 455 610 - 659
Violet 455 - 390 659 - 769

OK so now we have Temperature ratings and spectrum output.
What does it all mean. You may need to read this next aprt a couple of times. It's an excerpt from an article by Andrew Treveo-Jones:

"Yet another factor to consider is that different brands of lamps will have different output spectra and light output even if they are the same wattage and claimed colour temperature. You may even see differences between lamps of the same brand and same claimed colour temperature. Also,the claimed colour temperatures of lamps is only very approximate and gas discharge lamps don't really simulate theoretical black bodies.

Assuming that you are measuring each lamp under the same conditions and the sensor is not under reading blue light, you should still expect to see less PAR with lamps of the same wattage but with a higher colour temperature because there will be proportionally more photons with higher energy levels. As energy can not be created nor destroyed, the same amount of input energy (the wattage of the lamp) cannot produce more energy and so there will be fewer total photons produced by a lamp that has more blue light."

Clear as mud?
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Old 07-31-2010, 11:50 PM   #6
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All things considered, if the huge shadow from the middle brace bothers you then get another clamp on. If it doesn't stick with the setup you've got. But tbh.. if you've got the MH clamped right on top of the brace and the shadow is pretty big, i hardly doubt that MH is doing you any good.
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Old 08-01-2010, 03:55 PM   #7
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Ya, I have it on the left side slightly. So the blue actinic should stay if it can? And would I be good with just the MH if I get another fixture? The top of the tank is just so dang cluttered, if I don't need the T5 then I would like to get it out. But then I loose the sunset simulation as well, which I don't want. I just don't know.
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Old 08-01-2010, 04:03 PM   #8
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the sunset simulation is just for your personal preference. the corals don't care about it. you don't need it.
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Old 08-01-2010, 05:46 PM   #9
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Well the sudden sit to light or dark can spook some fish. So I wouldn't say the dawn/dusk simulation is only for human benefit. With my LED set up I have a 2 hour ramp up to 100%, 8 hours at 100%, then a 2 hour ramp down to moonlight. Granted only LED's can do that.

Kelso, can you hang the MH from the ceiling, or just clamp it on the back on one side? Then you can get a second one for the other side.
A MH should cover about a 2x2 area, so you will have some spillover, but that way you can lots of light into the tank.
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Old 08-01-2010, 07:01 PM   #10
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It can only clamp on. What is the benefit to mixing the T5 with the MH? It's a 14k bulb as mentioned. I am definatly getting another one, now I just need to know if I should bother putting a T5 strip with them.
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