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post #1 of 18 (permalink) Old 03-02-2009, 11:34 PM Thread Starter
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reflect upon this

anyone here know of, possess knowledge of, or can point me towards
a good source for reflector design. not looking to squeeze every last lumen out of a given bulb, but would like to be somewhat close.

Inf i feel i need is preferred distance from bulb to reflector surface

how far should reflector extend below 90* axis of a bulb to optimize Critical angle

am thinking a simple parabolic or arc reflector. while i realize this may not optimize the reflective light it should certainly get me in the area for next to no cost.

My thought was to use a large diameter PVC pipe cut in half.
Line it with aluminum foil, mount bulb at a point that would achieve most light reflected down towards water surface.

lights that are planned for use are 1 24" and 2 18"

Tank is a semi odd configuration corner tank, 24" to a side, and 24" deep.
The front side is offset 8" each side @ 90* from each side then approx 26" across the front. ( this makes it a 5 sided corner tank )
picture it like a Diamond with the point in the corner

My goal is to achieve between 1.6 & 2.0 WPG for this tank while staying below 70.00 total cost for lighting. Additional goals are simple to maintain, long life bulbs and low replacement costs. lets just say T8 bulbs to make it all simple.
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post #2 of 18 (permalink) Old 03-03-2009, 12:25 AM
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AHsupply reflectors are good. check em out ahsupply.com
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post #3 of 18 (permalink) Old 03-03-2009, 12:44 AM Thread Starter
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have looked at them, they would work well on a standard layout tank, this layout will be oddly shaped and prevents me from using standard sized reflectors
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post #4 of 18 (permalink) Old 03-03-2009, 01:18 AM
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Why couldn't you use mirror, like if you were doing a DIY canopy?
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post #5 of 18 (permalink) Old 03-03-2009, 02:54 AM
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Flourescent light bulbs are a glowing cylinder of light, not a line source of light, so there is no optimum reflector for them, and no mathematical formula for designing one. I think it is best to just do a simple line drawing of the bulb cross section (a circle), and start putting flat planes around it and ray tracing to see how they reflect. (Light reflects off a shiny mirror surface at the same angle from the vertical as it hits the reflector, so ray tracing isn't difficult. But, rays come from all over the surface of the bulb, not its centerline. Make the reflector so the bulb is up inside it far enough that you can't see the bulb or bulbs when you look up at it at the tank rim locations. That stops most of the light spillage. Then, just have fun playing with various configurations on paper. See http://tinyurl.com/dy2th4 for one possible configuration.

Don't use mirrors. Glass mirrors reflect a small percentage of the light that strikes them. You want a surface that will reflect 90% of the light, like really white paint, or shiny aluminum.

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post #6 of 18 (permalink) Old 03-03-2009, 12:40 PM Thread Starter
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mirrors i was aware of, also was very surprised about the white paint, Aluminum foil is my current thought, maybe laid onto the inner surface of something like a 4" or greater pvc cut in half, then that half cut in half and seperated by approx the width of the bulb?

So up inside the arc enough to prevent light spillage, no magic numbers/values to watch or start at.

sounds like simple trial and error will be the order of the day
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post #7 of 18 (permalink) Old 03-03-2009, 01:28 PM
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Quote:
Originally Posted by Florida_Larry View Post
have looked at them, they would work well on a standard layout tank, this layout will be oddly shaped and prevents me from using standard sized reflectors
If you plan to use standard size bulbs, what's to keep you from using standard size reflectors? Or just cut them down if need be.


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post #8 of 18 (permalink) Old 03-05-2009, 03:40 AM Thread Starter
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If you plan to use standard size bulbs, what's to keep you from using standard size reflectors? Or just cut them down if need be.
The shape
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post #9 of 18 (permalink) Old 03-05-2009, 04:20 AM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
Flourescent light bulbs are a glowing cylinder of light, not a line source of light, so there is no optimum reflector for them, and no mathematical formula for designing one. I think it is best to just do a simple line drawing of the bulb cross section (a circle), and start putting flat planes around it and ray tracing to see how they reflect. (Light reflects off a shiny mirror surface at the same angle from the vertical as it hits the reflector, so ray tracing isn't difficult. But, rays come from all over the surface of the bulb, not its centerline. Make the reflector so the bulb is up inside it far enough that you can't see the bulb or bulbs when you look up at it at the tank rim locations. That stops most of the light spillage. Then, just have fun playing with various configurations on paper. See http://tinyurl.com/dy2th4 for one possible configuration.

Don't use mirrors. Glass mirrors reflect a small percentage of the light that strikes them. You want a surface that will reflect 90% of the light, like really white paint, or shiny aluminum.
I had read your posts re: the white paint, aluminum and mirrored surfaces, very enlightening to say the least, i did as suggested and found some ray tracing software. The results after a bit of fiddling was impressive, the light source needs to sit far higher into the reflector than i had originally imagined, and also found by placing a 45* angled point at exactly the 0* point re strike was nearly totally elated on my limited layout.

I am impressed looks like a simple 6" arc with a 45* point directly above the bulb will fit the bill nicely. Surface of the bulb from the surface of the reflector will be approx 1/2" per my crude settings, will do a new layout and try and get the values closer, but dont really think that is necessary, Not looking for nth% degree accuracy here, just fully functional

Looks like so far costs are 40.00 for 2 electronic ballasts, 3.79 * 3 for the three bulb fixtures and 5.00 for 5' of 6" PVC pipe.

so i have 1 15w OD * 1.4, 1 15w NO, and 1 18W NO.

so the next question is how would you calculate WPG on a tank shaped like a diamond.

The 18W runs the full 24" side 1, 4" off the side
1 15W runs the remained of side 2 4" off the side

The OD 15w runs parallel to the front 4" off the front

I ( may be incorrect here ) used the following method, please someone chime in if this is in error, or you know of a better method.

Light 1 ( 18W ) covers an area 8 x 24 x 24
8*24*24=4608 cubic in volume /238 ( 1 gal covers approx 238CI )= 19 gal less volume taken by gravel etc of 10% 19.0 -1.9=17.1
so assuming a standard fudge factor on T8's of 1.4 * 18w = 25w/17 gal = 1.47 WPG

Light 2 ( 15w ) covers an area 8 x 18 x 24
8*18*24 = 14.5 gal less 10% = 13 gal Light output = 15w*1.4= 21w/13g = 1.6 WPG

Light 3 ( 15W OD ) covers an area 18 x 24 x 6 ( this is also the least plant populated area of the tank )

18*24*6=10.8g less 10%= 9.8g
15w [email protected] 1.4= 29.4W/9.8g= 3WPG

so left side = 1.47 WPG
right side = 1.6 WPG
Center = 3.0 WPG
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post #10 of 18 (permalink) Old 03-05-2009, 04:25 PM
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3M makes a very reflective tape. It's so sticky it will stick to anything. It's about 2 inches wide so you can put it on any light fixture. I use it and it seems to work well.

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post #11 of 18 (permalink) Old 03-05-2009, 07:37 PM
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Forget about watts per gallon, and think about the distance from the bulb/reflector down to the substrate. That is the most important dimension. Unfortunately I don't know how much intensity you get from any of those bulbs at any distance from the bulb. But, I suspect that you will have low light, even with the reflectors, because of the 24 inch height of the tank.

If you use T5HO bulbs you will probably have enough light to grow almost any plant.

Hoppy
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post #12 of 18 (permalink) Old 03-05-2009, 08:29 PM
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http://www.naturallighting.com/web/shop.php?crn=809

Hoppy suggested Miro 4 to me. Reflects way more light than the aluminum tape. I got the 48 x 9.5 sheet. It was a little tough to shape, but I did it by hand on a square edge of my breakfast bar. Cutting it was easy, used a pair of kitchen shears. Also a good place for T5 ballasts. Reefgeek has cheaper T5 ends.

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post #13 of 18 (permalink) Old 03-05-2009, 09:53 PM
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Reefgeek has cheaper T5 ends.
Since you mentioned end caps: Unless you plan on dipping your fixture into your tank, skip the ridiculously expensive waterproof end caps (don't forget the mounting brackets!). Just buy regular T5 end caps. A few retailers carry them, but I think DIYReef has the best price on t5 end caps.
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post #14 of 18 (permalink) Old 03-05-2009, 10:57 PM Thread Starter
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Quote:
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Forget about watts per gallon, and think about the distance from the bulb/reflector down to the substrate. That is the most important dimension. Unfortunately I don't know how much intensity you get from any of those bulbs at any distance from the bulb. But, I suspect that you will have low light, even with the reflectors, because of the 24 inch height of the tank.

If you use T5HO bulbs you will probably have enough light to grow almost any plant.
true, depth alone may in fact require i make that shift.
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post #15 of 18 (permalink) Old 03-06-2009, 03:50 AM
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You have gotten a lot of great advice here, but thought I would throw this out there. The program found at the link below was designed for solar collectors, but I think it could work for our purposes as a reflector instead.

This is taking the light and concentrating it on that focal point, but my thought is, why couldn't it work the other direction and reflect light out from the focal point?

I am no physicist studying light particles, nor do I understand everything regarding light and photons, and all that makes them up, but it seemed like a sound idea. I will let the group be the judge.

http://mscir.tripod.com/parabola/

Have a good one!
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