MH lighting is a myth

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Thank you all for your comments.
I do not think using quadratic equations are going to be a good model for this. I suspect a calculus equation involving some trigometric functions is probably the right direction.
I was kinda hoping someone that deals in this area, say Andy!, might give a reply.
Andy--how do your measure light output from various types of sources when you engineer your ballasts? What are the implications for aquarium use?
And does anyone know of readings being done underwater at the depths we are interested in? I know somewhere way back I saw some on depths in the ocean with sunlight. But how about using the artificial sources?
And finally, the lumen figures in the original post were just off the top of my head as a place to start. But the distance over the water figures are from what I have observed. Now I have seen two people say they are putting MHs much closer to the surface.
I had thought that putting MHs this close was asking for problems with water and fish comming into contact with a very hot piece of thin glass. I would like to here more from you on this.
Thanks alot folks.
b.
 
Someone is going to have to find out about the diffusion properties of water as well. If we want an accurate calculation we're going to have to apply the properties of water and not assume that the water behaves in a similar manner to air.

In addition, the turbidity of the water is key as well. FWIW, In the Baensch Marine Atlas Vol-1 Baensch has a half-assed calculation for "required wattage" and there is a table for "pollution factor". At 30cm 100% Clear water has a "polution factor" of 86 (Obviously not a particularily profound number).

Just trying to see that this question does get answered to bmw's standards, as I am quite interested in the physics involved here as well. I just want to see the raw calculations not "Metal halide is good." :rolleyes:

All in all, great question bmw!

Andrew
 
I'll add some less technical notes to this number crunching thread. Comparing a MH light source to the sun is interesting but not perfect. In the ocean if two objects are 6 inches apart they'll both be equally lit. In a tank where the point source is a foot away one object may be fully lit, the other only 1/2 lit. Point source in a tank = shadows, linear source = relatively no shadows.

Small correction TheDonger, when you say the "filament produces the light". Before you turn your MH on check it out. The arc exists without a filament. I also agree, the ripple effect is great and closest to what you observe snorkeling.

As far as measurements I'd look to someone like Richard Harker. He describes his methods in a linked article on IceCap's MH page. When you add water penetration to the mix you appreciate what started the 10K+ movement, as this is the spectral portion of light that goes deepest when full spectrum light is observed.

Andy
 
canadian...my thoughts too
does the inverse square law apply at the same ratios for air/water
i still like my halide. law or no law, corals like it 10x more than the no/pc's i had before.

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"Keep It Clean"
 
I have to agree with Megadeaths analysis.

Water/Air ok fine the numbers might be different but both the MH and the VHO's light is going through the same medium (it has to for this to be a valid discussion).

Second I think that a Luxmeter is what is needed to end this debate.

Ok... to add to this mess, is lumens what should be measured to determine the most benifit light has on coral. And which types of coral? Does UV play a factor? What about alklinity in coloring and water that has more undissolved or dissolved organics than other water. All this will have an effect one way or another.

Thanks Megadeath for the math. I agree with your analysis. And I too run MH with supplimental lighting. IN MY EXPERIENCE it is the way to go.



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BW

'Semper Ubi Sub Ubi'
 
Hi Andy,
Thanks for the response. I have seen Harker's articles. But he was measuring differences in the icecap ballast and tar ballasts. Do you think you could dig up some figures on on light intensities Icecap measured for vho and MH, in terms of lumens(or lux)and the parameters involved in the measurement? Would it help to say I am a customer :)
Thanks,
b.
 
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality."--Albert Einstein

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Visit Keith's Reef
 
What units are the inverse law dealing with? Some of you guys are using feet (meters) some inches (centimeters). I have a book that states the earth's surface receives 2000 muE/m^2/s (metric) or PAR which is roughly equivalent to 100,000 LUX or 10,000 foot candles. If the formula uses meters (feet) then the light lost in air above the water is negligible from 4-6" if it uses cm or inches then the light lost at 2" is great. How does lumens fit into the picture? (been 10 years since I did college physics) :D Evan and I have been arguing about this for weeks someone please help us.

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"Honey, put the bleach down and step away from the reef tank. I promise we will spend more quality time together."
My Bonsai-reef site
 
Mega,

Does inverse law account for the medium that the lighting has to penetrate? Is it assuming distance through air? Seems like there should be some type of coefficient to account for this. Also, the units you used with Inverse's Law do not match the units used at the website you referred to. Can you please explain this?

TIA BUD
 
Unit of measure doesnt matter, see the "are there any physics major's in the house post" Yes, medium the light passes though does matter, but at the depths we are dealing with, not very much, short of a algae bloom. That said, Bretton WAde sp? has a java program that will calculate the K in water as depth drops & effects of water clarity on this. First things first though, the formula is a BEST case for dropoff. L8r mega

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members.xoom.com/megareefs
Yup, new url, finally thumbnail index html's on the folders, and a streaming webcam!
 
If I had lux I would use it, I now have par for 250/400 halides as I said above, but I do not for vho/pc/no so for compairson it wont work. L8r mega

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members.xoom.com/megareefs
Yup, new url, finally thumbnail index html's on the folders, and a streaming webcam!
 
Mega,

lux = lumens per mÃ"šÃ‚². As I said in the other thread, lumens don't make sense. Like measuring pressure in pounds, it doesn't work.
 
Tadashi,

I'm not sure what the relevance is of the amount of light that hits the earth. The sun is so far from the earth, relatively, that the distances we are talking about will make no difference in the intensity of light from the sun.

However, the inverse square law still holds for the sun. If you could get twice the distance from the sun, as the earth is, you'd only have 25% as much light.
 
I used the sun measurement as a reference. PAR has metric values in it. I am not sure about lumens or foot-candles. I know that the inverse law is geometric but to get the right units you must measure correctly. TO determine the PAR from 1 cm versus 1 m would make a difference in the formula.

The next chapter in the handbook of the previous link explains how the different units play into the measurements.

Has anyone seen this: http://www.masla.com/dana01.htm
They state that PAR is a more relavent measurement since it measures the entire band of light versus Lux.

I am still tyring to read all this and understand everything.

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"Honey, put the bleach down and step away from the reef tank. I promise we will spend more quality time together."
My Bonsai-reef site
 
Dont worry atj, I completely agree with you, unfortunatly I am unable to find lux or better yet par levels for vho, pc, no, and 175w halide bulbs, so I used lumens for the posts here, in my database, I have par for the bulbs that I use. L8r mega

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members.xoom.com/megareefs
Yup, new url, finally thumbnail index html's on the folders, and a streaming webcam!
 
Tadashi,

The inverse square rule is a relative thing and the units are irrelevent. Much like specific gravity (now theres a discussion we could start).

If you double the distance you quarter the light. It doesn't matter if you go from 1m to 2m or 1" to 2" or 1cm to 2cm. In all cases the light intensity will be reduced by 4.

Look at the second formula in the handbook. E1.D1**2 = E2.D2**2 as long as the units on both sides of the equation are the same it doesn't matter what they are as long as they are a unit of length.

BTW, lumens and lux are derived SI units and so are considered "metric". lux is lumens per square metre.


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ATJ
http://atj777.tripod.com/
 
Mega,

lumens is used to measure light output. lux is used to measure light intensity. Lamps are rated in lumens because this is how much light they output - it is an absolute number. You won't find lamps rated in lux because it doesn't make sense. The best you could hope for is a rating like 800 lux at 1m from the light source.

That's why I'm worried about your calculations. While they may be useful for comparing one distance from a light source to another distance, the values you have calculated are meaningless.

How are you going from the rated output of the lamp, to the values at a certain distance?


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ATJ
http://atj777.tripod.com/
 
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