Light Intensity in an aquarium

VaughnH

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Carissa;25436 said:
Same tank and reflectors - different bulb types? Maybe that would be difficult without removing the fixture though....but you could do T8s and T12s on the same fixture if you had two bulbs of the same size.

The only two fixtures I have are the two I tested. If I had saved the ballast and end caps from the little 10 gallon fixture I could hook it back up and see what a 15 watt linear tube does, but I didn't have the foresight to save the parts. I usually save everything, but this time I decided to not be a pack rat.

Today I'm going to try something else to see why I have such weak light from that 10 gallon fixture: The original Perfecto hood has a glass installed under the light fixture, which means a lip in the plastic to hold the glass. I removed the glass, but left the lip. That may be acting as an aperture to reduce the light getting through the opening. I can check that pretty easily.

That 10 gallon tank is now showing me what green water looks like.
 

VaughnH

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Well, once more the value of a good light meter is demonstrated. I looked carefully at my modifiied Perfecto hood/light fixture. The opening for light to get into the tank from the fixture was originally 3 inches by 18.25 inches, but this was with a .38 wide lip all around the opening.

I set up the light fixture on the same wood stand I used for my original light measurements, but with the hood included. As might be expected I got less light than with just the light fixture. So, I used a utillity knife to trim off the lip, increasing the area of the opening by 30%, and measured the light intensity again. As expected it increased due to the larger "aperture". Here is what the hood looks like, with the lip half cut out:
IMG_1639.jpg


And, the PAR meter data:
10GalApertureEffect.jpg


If I now replace the mylar reflector material with aluminum foil I should get the results shown by the red dashed line, a big improvement over what I started out with for this fixture. Just by looking at the light I can't say the differences were visible, but the meter is much more sensitive than my eyes.
 

orion2001

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That seems about right Vaughn. If you remember, a while back I had asked you how you rated the perfecto hood because of the narrow cone of light that emnates from it due to this aperture effect. Currently I have 2, 10 gallon tanks, one with the Perfecto hood and the other with the other cheap walmart hood ( Incandescent Aquarium Lighting: All-Glass Economy Full Hood) . I tested both the hoods against a white surface, and although I had to go by what my eye told me (very inaccurate method of comparison), the difference was large enough that I could see it visually. The other great thing about the 2nd hood is that if you pry out the ultra cheap metal "reflectors" (they don't reflect at all...they have a matte finish), and then stick aluminum foil on the inside of the entire hood, this acts as a much better reflector than the reflector in the perfecto hoods which are simply too narrow, giving rise to additional re-strike. These hoods have a lot more space between the bulbs and the hood thus making them marginally better reflectors IMHO.

Sorry to hear about your 10 gallon tank. Are you dealing with GW right now? Do you have any ideas as to why you are having this GW issue in your tank? I'm always curious as to the reason why these things happen.
 

VaughnH

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orion2001;25457 said:
Sorry to hear about your 10 gallon tank. Are you dealing with GW right now? Do you have any ideas as to why you are having this GW issue in your tank? I'm always curious as to the reason why these things happen.

That tank is now getting very little care, since the plants have been just sitting their doing nothing. I suspect the green water came from pond snail epidemic I had and too many died at once. But, I'm not at all sure. In a day or so I will try to clean it up and get rid of it.
 

orion2001

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VaughnH;25459 said:
That tank is now getting very little care, since the plants have been just sitting their doing nothing. I suspect the green water came from pond snail epidemic I had and too many died at once. But, I'm not at all sure. In a day or so I will try to clean it up and get rid of it.

Sorry, did you mean get rid of the GW or the tank itself? I'm a little worried about how things will go with my tank once I submerge things. It is pretty much exactly identical to yours. I will have had dwarf hairgrass grown for two months emersed (it is doing quite well) and I plan to have anubias coffeefolia, java ferns, rotala rotundifolia and some hornwort to get things started. Your lack of growth is a little worrying as I have similar substrate, lighting and dosing plans.
 

VaughnH

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orion2001;25460 said:
Sorry, did you mean get rid of the GW or the tank itself? I'm a little worried about how things will go with my tank once I submerge things. It is pretty much exactly identical to yours. I will have had dwarf hairgrass grown for two months emersed (it is doing quite well) and I plan to have anubias coffeefolia, java ferns, rotala rotundifolia and some hornwort to get things started. Your lack of growth is a little worrying as I have similar substrate, lighting and dosing plans.

For the moment I only want to get rid of the green water, but I'm close to getting rid of the tank too. I purchased the tank only for some experimenting I wanted to do - another subject that could be explored in some depth here. So....why not? I'll start another thread.
 

Tom Barr

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Vaughn, if you need to borrow the 15 W hang on UV....just ask:)
Then you can learn all you want about GW.......


Regards,
Tom Barr
 

Carissa

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A while back I changed my ballast to overdrive my lights and I was very interested to know if there would be a significant difference in light output. Without having a light meter I couldn't determine this with much accuracy, but what I did do was set up my SLR camera on a tripod and turned it on manual setting....took a picture and recorded the settings I used. Then afterward, took another picture on identical settings. Then I could clearly see that there was indeed an increase in light by comparing the two pictures, although without that I wouldn't have been totally sure just by my eye.
 

VaughnH

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If you limit testing of light fixtures to out of the water tests you can use several different kinds of light meters, including a manually set camera. You could take a few photos, each one stop (2X) exposure different, for each configuration. Then by matching the photos anc comparing the f stops you could say one fixture is 2X, or whatever, better or worse than another. Or, you could use an incident light photo meter, just as I used the PAR meter sensor. I had at least three suitable light meters back when that was how it was done, but got rid of them years ago.
 

orion2001

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VaughnH;25477 said:
If you limit testing of light fixtures to out of the water tests you can use several different kinds of light meters, including a manually set camera. You could take a few photos, each one stop (2X) exposure different, for each configuration. Then by matching the photos anc comparing the f stops you could say one fixture is 2X, or whatever, better or worse than another. Or, you could use an incident light photo meter, just as I used the PAR meter sensor. I had at least three suitable light meters back when that was how it was done, but got rid of them years ago.

Do you think it would be accurate to take grayscale images and digitally compare pixel brightness values? I guess you could do a lot of manipulations digitally, such as image the difference of the two photographs to compare spread and intensity differences, etc.
 

VaughnH

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When you are just comparing two or more setups there are several ways to do it without the PAR meter. It is when you want to compare to some standard or compare to someone's tank in another state that you need a PAR meter. Then, of course, in-the-water measurements would be preferable too.
 

VaughnH

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I have been thinking more about the question, does the light intensity drop off differently for long linear bulbs than for short "blob" bulbs. I downloaded some log log "paper" from the internet and replotted some of the data I took - the center line of the tank from the substrate level up to near the plane of the bulbs. Here is what it looks like:

PARvsDistance.jpg


I think it is clear that there is a different drop off rate for the two fixtures I tested. And, it appears that the almost linear AH Supply PC bulbs appear to lose intensity inversely approximately proportional to the distance from the bulb. But, the CFL screw-in bulbs seem to lose intensity approximately proportional to the inverse square of the distance. As you get close to the plane of the bulbs, the relationship seems to break down, and that is explainable because the "linear source" is less and less a linear source as you get close to it. The same is true of the "blob" source. I'm sure these relationships break down at the ends of the tanks too for obvious reasons.

This isn't proof of anything, but it does suggest to me that one reason for the effectiveness of T5 bulbs is that they are close to true linear light sources. And, to me it suggests an explanation for why people can successfully use what appear to be way over powered MH bulbs - they are suspended further above the tank, and their very high light intensity drops to a reasonable level as you do deeper into the tank. It makes me also think that the ability of MH fixtures to "penetrate" deep tanks is largely because they are so bright to start with.

I think maybe I have now squeezed out all that I can from the data I took.
 

wiste

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When you are just comparing two or more setups there are several ways to do it without the PAR meter. It is when you want to compare to some standard or compare to someone's tank in another state that you need a PAR meter. Then, of course, in-the-water measurements would be preferable too.

Comparison can be made using a Lux meter to get performance results between someone's tank in another state. When comparing light performance the in-the-water measurement might not be the way to go to get meaningful data concerning the lights being used as the water clarity would have a significant effect.

If using a light meter for comparison results how do you calibrate the meter?

Regarding the mylar being tested, was there a reflectivity rating?
Some mylar is advertised as having a 98% reflectivity and other mylar does not advertise a rating.
 

VaughnH

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wiste;25720 said:
Comparison can be made using a Lux meter to get performance results between someone's tank in another state. When comparing light performance the in-the-water measurement might not be the way to go to get meaningful data concerning the lights being used as the water clarity would have a significant effect.

If using a light meter for comparison results how do you calibrate the meter?

Regarding the mylar being tested, was there a reflectivity rating?
Some mylar is advertised as having a 98% reflectivity and other mylar does not advertise a rating.

I got the mylar from another aquatic plant keeper, left over from a project he did, so I don't know what it was advertised to be. It is 3 mil thick, and doesn't transmit light through it, as a lot of mylar does, plus it is aluminized on both sides. All of that tells me it has high reflectance.

I have often been told on various forums, by experienced people, that mylar is not nearly as good a reflector as it seems to be. Being a skeptic I chose not to believe that. The stuff just looks so good! Compared to aluminum foil it looks like a much more efficient reflector, but that is a trick our eyes play on us. We judge a reflector by how true the reflection is, by how much it looks like a great mirror to shave by. And, that has nothing at all to do with how good the reflectance is.

I would like to say from now on I will believe what experienced people tell me.........but I'm sure I won't. Incidentally, experienced people by the dozens, also tell me that white paint is a great reflector, but with my superior knowledge I laughed that off too. Wrong again. But, I also assured a lot of people that Senator Obama could never possibly win the Democratic Presidential nomination. And, back in 1989 I assured a lot of friends that the San Francisco Giants would beat the Oakland A's in the world series. To my credit I did predict that Sacramento summers would see little or no rain.
 

rvilalriba

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Lux Meters usage in Aquarium

Hi, I've got a LX-1020B & an LX-1330B lux meters that I've used for photography (outdoor & indoor) but i was wondering if this have a use in aquarium either in light fixtures on the aquarium or in aquarium photography. I've reading about this light meters for aquariums and it got me more confused i just want to know if these type of lux/light meters can be use in aquariums in any way.

link for 1020B & 1330B light meters:
DIGITAL LIGHT METER 100,000 LUX LCD LAB PHOTO CAMERA - eBay (item 330242481267 end time Jun-14-08 00:40:47 PDT)
NEW DIGITAL LIGHT LEVEL METER 200,000 LUX PHOTO CAMERA - eBay (item 330243179304 end time Jun-16-08 15:03:15 PDT)

any information to enlighten me is very much appreciated. many thanks in advance.
 

SpeedEuphoria

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Very Good thread and info!

I wish you could have also tested 1 other reflector material, aluminum tape. I am currently using this and seems to be OK(which doesn't mean much, lol). To the eye it seems close to aluminum foil but may not be quite as good?

Anyway I guess just something else to test(prob wont ever be tested, just food for thought). its $3 for a roll and easier to use because its tape.

I currently have a 10G with a similar hood and its modded, at 1st I just used aluminum foil on the stock 15w T8 tube. I think this would be another great comparison test. To me it seems like the loss of light from the spiral bulbs may mean that the stock 15w bulb and alum foil is just as good as 2x 13w spiral screw in bulbs with foil?.

So far I have just cut the excess silicone away from that narrow "window" in the hood, I guess I need to cut the plastic also to get a little more(thanks to this thread)

For my 10G I made some reflectors out of 44oz plastic cups, covered with the alum tape. It gives an OK parabolic effect, but the bulbs are too large in diameter along with the narrowness of the plastic fixture to use them effectively.Currently with this setup (no CO2) I get green dust just on the sides of my 10G.
Picture040.jpg



I believe that using a "U-shaped" bulb would be better for these fixtures, they are just harder to find with "daylight" ratings. I also think these T10 screw in bulbs would be the best bulbs possible for this type of setup, even harder to find except for the standard 7w, except for these 20w:
Mini Power Compact - Colormax - 20W - 8 in. | Compact Fluorescent Straight Pin Bulbs | Bulbs & Lamps | Aquarium - ThatPetPlace.com
 

Carissa

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That's a good idea about the tape, I hadn't thought of that. Affixing regular old aluminum foil to light reflectors can be frustrating to say the least. :)
 

defdac

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It was quite interesting to use a Lux-meter sitting at the bottom of a tank without water and then start filling the tank up.

I was very obvious the water made the tank act like a opto fibre =)

Regarding the difference between Lux- and PAR-readers the measure kindof the same range, only that Lux-meters are not that sensitive to blue and red light.

Lumens are emitted inside the PAR-range (400-800 nm though, so if you know the spectral distribution of your light you could actually with some mathematics convert the Lux-measure to a PAR-reading.
 

VaughnH

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A lux meter wouldn't give you an accurate reading of light intensity, but it would give a good indication of the distribution of intensity around the light or in the water, or in the water vs in air. Just a thought: doesn't every bulb have a fixed relationship between lux and PAR, based on the spectrum produced by the bulb? That would be a number, like .26 PAR to Lux, and of course it would apply only to new bulbs. Is that right? If so, we should urge bulb manufacturers to provide that for every bulb.