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.

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:


And, the PAR meter data:


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.

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.

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.

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.

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

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.

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.