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Discussion Starter #1
Good morning,

I am in the process of making my own reflectors for 36W PL-L compact fluorescents and I am wondering what is the shape that will give me the more light. Since the CFL we use are biaxial (two tubes) unlike T8 fluos, is the typical parabolic reflector adequate?.

I thought of these three designs, which do you think is best?.



Also, what position should I put the CFL inside the reflector, higher or lower as seen in the next pic??.



And finally, what about putting them in vertical position?, this would allow more space for the light coming from the reflected surface to get out without hitting back the tubes.



Greetings from Spain.
 

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For the reflectors the second one seems to the best, the thrid relfector has the same shape but the fold in the middle might increase restrike.
Positioning the bulbs, the second choice is also the best option as it will run cooler and it will get the best out of your reflectors. And you should position them horizontally so that they don't heat up quickly.

But I ask, since you're in Europe why not use T5? It's the exact same thing as PC but with a better shape, uses less space, and they run cheaper.
 

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Hello Raul7,

I am going to use 90 mm diameter PVC pipes cut in half, so that would give me the first reflector of the three I´ve shown, a perfect semi-circumference, I have used them with success in the past, but as you said, the slightly more parabolic one should focus the light much better. I could heat the PVC to give it the shape I want.

Last time I checked T5 were much more expensive than CFL of the same wattage, not to mention you must use electronic ballasts. With CFL you can use much cheaper magnetic ballasts up to 36w and I´m on a student budget :?

Is heat the only drawback in the vertically positioned CFL?. I could leave a small gap on top of the reflector to let air flow, and also, aren´t CFL supposed to run better at somewhat higher temperatures? (optimum light output is at 35ºC if I remember correctly, 25ºC for T 8).

I think I will coat the inside with mylar if none suggests something else.
 

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The only way to know is to draw your vectors.
You assume that the center of each bulb radiates as a point souce.
You consider any restrike that hits the bulb to not reflect

Use the simple law or reflection
angle of incidence=angle of reflection

Take a look at my article on a DIY reflector. It shows an example of such ray tracing.

http://www.aquaticplantcentral.com/forum/cms_view_article.php?aid=16
 
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