DIY Effective Reflector - The Planted Tank Forum
 
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post #1 of 13 (permalink) Old 02-20-2014, 08:22 AM Thread Starter
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DIY Effective Reflector

I am trying to build an effective yet cheap reflector for my 10 Gallon tank that has 4 anubias plants and some java moss in it. I decided to go for LEDs on my larger tank but the economics of it don't add up for the smaller tank.

I intend to use consumer CFL lights. I have read a lot of conflicting opinions on whether horizontal or vertical reflectors are better for the job. I intend to use the straight tubes CFLs and it seems that horizontal reflectors are better for these. (The alternative is using spiral CFLs and vertical reflectors are reported to be better for these ones.)

As my tank already has a hood, I intend to place the reflector and lighting in the space provided in the hood for lighting (see attempted drawing).

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My idea was to use an empty plastic bottle of soda (large 2 litre ones), cut the bottom and top so that I am left with a symmetrical semi circle, cut along one side of it, cover one semicircle with aluminum foil and use the other transparent side to spread the light (like a lens of sorts). An alternative is to cut the bottom part and shorten it sightly for a narrower/wider angle (not sure).

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Any advice on reflective material would be appreciated. Also whether I should have a "optic lens" is a matter I am not sure about. Any advice would be appreciated.
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post #2 of 13 (permalink) Old 02-20-2014, 02:58 PM
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i think your design is probably the opposite of efficient. the circular reflector would do a poor job reflecting light, and the soda bottle plastic would certainly do a terrible job of spreading the light.

Some folks on the forum have done a lot of research on lighting and reflectors. white paint appears to work very well for reflecting light, and going with a reflector with some bends seems to increase the amount of light reflected to downward.

i can't find the threads at the moment, but hopefully someone else, like Hoppy, can chime in and set you on the right path.


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post #3 of 13 (permalink) Old 02-20-2014, 03:46 PM
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One recent thread that I remember - https://www.plantedtank.net/forums/sh...449&highlight=

This may, or may not, be of interest.
www.reflector-design.com
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post #4 of 13 (permalink) Old 02-20-2014, 03:58 PM
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Here is a simplistic, but very effective way to judge a reflector: Look at a bulb, which is mounted in your light fixture. Do you see just the bulb, or do you have to look carefully to pick out the real bulb from the reflections of the bulb from the reflector? Each reflection of a bulb is the same as another bulb, as far as how much light you are getting is concerned. Think about it. When you see a reflection of the bulb you are seeing light from another surface of the bulb, so it is light that would not be present if you didn't have the reflector.

If you have a reflector which shows you a full image of the bulb on each side of the bulb, that would be the same as having 2 more bulbs installed, and no reflector. (Not quite the same, but just assume it is the same.) And, if you see two full reflections of the bulb, on each side of the real bulb (not partial reflections, but full reflections) that is the same as having 4 additional bulbs installed.

So, the ideal reflector is one that lets you see multiple reflections of the bulb alongside the real bulb.

I did some testing with a simple sheet aluminum reflector shaped like \_/, with the bulb in the middle. I bent the side "flaps" so I could see 3 bulbs instead of just one, a reflection on each side of the bulb. This reflector doubled the PAR I measured with that light. I did this with more than one type of bulb, too.

Look at the AH Supply reflector:


This is shaped to give 2 reflections of the bulb on each side of the bulb (but only partial reflections because of the dual tube type of bulb) It is one of the best reflectors you can buy.

So, to make a good DIY reflector, just use aluminum flashing material - thin aluminum sheet, which is shiny. Bend it, using a couple of boards and a clamp or two, to a \_/ shape, adjust the angles of the bends so when you look at the bulb, you see 3 bulbs, not just one, and you have a good reflector. Polish that aluminum as well as you can so it has a mirror finish, and you have a better reflector.

Hoppy
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post #5 of 13 (permalink) Old 02-20-2014, 11:17 PM
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If you're light source was a point/line infinitely thin, a parabola with the light source at the focus would be the best shape for a reflector.

Unfortunately, our options for lighting aren't very thin, let alone infinitely thin, so if you were just using a straight parabola, a lot of the light would just get reflected back into the bulb...

Greystoke did a pretty thorough posting about reflector shape a while back:

https://www.plantedtank.net/forums/sh...ight=reflector

Easiest would probably just spraypaint the inside of the hood white with krylon fusion.

For just a 10 gallon, you'll get plenty of light from CFLs, enough that you probably don't even need a reflector (although using one would allow you to go with smaller bulbs maybe...).

My first planted tank was a 10 gallon that I stuck CFLs in, and I coated the inside of the hood with aluminum tape. It worked pretty well, but if I were to do it again, I'd use white spraypaint.
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post #6 of 13 (permalink) Old 02-21-2014, 12:22 AM
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Quote:
Originally Posted by lochaber View Post
If you're light source was a point/line infinitely thin, a parabola with the light source at the focus would be the best shape for a reflector.

Unfortunately, our options for lighting aren't very thin, let alone infinitely thin, so if you were just using a straight parabola, a lot of the light would just get reflected back into the bulb...
It isn't necessarily true that, even for a point light source, a parabolic reflector would be the best choice. If the goal is to produce a parallel beam of light, which can travel long distances without great loss in intensity, a parabola is the best choice for a point source of light. But, if you want to capture as much of the emitted light as you can, and get it well distributed over a relatively close surface, a set of flat reflectors may be a better choice. For our real world situation, with large area light sources, we want to capture as much of the light from those sources as we can, and direct it to the substrate of the tank, as evenly distributed as possible. That seems to always lead the designer to a set of flat reflectors - see the AH Supply reflector, for example.

A "perfect" reflector, in the conventional sense, would cast an accurate image of the light source on the target for the light. In other words it would produce a very non-uniform distribution of the light. I think that is why you rarely ever see a parabolic reflector used on a high quality aquarium light.

Hoppy
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post #7 of 13 (permalink) Old 02-21-2014, 06:07 AM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
Here is a simplistic, but very effective way to judge a reflector: Look at a bulb, which is mounted in your light fixture. Do you see just the bulb, or do you have to look carefully to pick out the real bulb from the reflections of the bulb from the reflector? Each reflection of a bulb is the same as another bulb, as far as how much light you are getting is concerned. Think about it. When you see a reflection of the bulb you are seeing light from another surface of the bulb, so it is light that would not be present if you didn't have the reflector.

If you have a reflector which shows you a full image of the bulb on each side of the bulb, that would be the same as having 2 more bulbs installed, and no reflector. (Not quite the same, but just assume it is the same.) And, if you see two full reflections of the bulb, on each side of the real bulb (not partial reflections, but full reflections) that is the same as having 4 additional bulbs installed.

So, the ideal reflector is one that lets you see multiple reflections of the bulb alongside the real bulb.

I did some testing with a simple sheet aluminum reflector shaped like \_/, with the bulb in the middle. I bent the side "flaps" so I could see 3 bulbs instead of just one, a reflection on each side of the bulb. This reflector doubled the PAR I measured with that light. I did this with more than one type of bulb, too.

Look at the AH Supply reflector:


This is shaped to give 2 reflections of the bulb on each side of the bulb (but only partial reflections because of the dual tube type of bulb) It is one of the best reflectors you can buy.

So, to make a good DIY reflector, just use aluminum flashing material - thin aluminum sheet, which is shiny. Bend it, using a couple of boards and a clamp or two, to a \_/ shape, adjust the angles of the bends so when you look at the bulb, you see 3 bulbs, not just one, and you have a good reflector. Polish that aluminum as well as you can so it has a mirror finish, and you have a better reflector.
thank you for the insight and the suggested reflector shapes.

My problem is more with the amount of space I have under the hood and whether I can do the above designs in that space. They seem to need more space and or more height?

also, is the \_/shape better or the you mentioned from AH Supply? if the AH supply is better, why not attempt to make this? is there a specific angle to the edges that allows such efficiency which is not known hence the \_/ is easier?

Also, in the \_/ design, does the angles of the edges matter? How wide/narrow should the bends be?
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post #8 of 13 (permalink) Old 02-21-2014, 06:10 AM Thread Starter
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On a separate note, is this for horizontally laid out cfl tubes (according to the diagram it appears to be so)? I read somewhere that spiral CFLs are more efficient vertically but the tubular CFLs horizontally. Can anyone confirm?

Will these reflector designs work on vertically mounted CFLs as well? Do the angles need to be altered for vertical vs horizontal?
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post #9 of 13 (permalink) Old 02-21-2014, 02:51 PM
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I have read (on these forums) that aluminum foil doesn't do well as a reflector. You could try some Mylar from a hydroponics store, it is quite reflective and intended for maximizing light.
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post #10 of 13 (permalink) Old 02-21-2014, 02:57 PM
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For anubs and java you don't need to be nerding out with optimizing your reflectors. 2 13w CFL's would be more than plenty light for your setup/plants even with no reflectors.


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post #11 of 13 (permalink) Old 02-21-2014, 02:59 PM
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Quote:
Originally Posted by aquariumhobbyist View Post
thank you for the insight and the suggested reflector shapes.

My problem is more with the amount of space I have under the hood and whether I can do the above designs in that space. They seem to need more space and or more height?

also, is the \_/shape better or the you mentioned from AH Supply? if the AH supply is better, why not attempt to make this? is there a specific angle to the edges that allows such efficiency which is not known hence the \_/ is easier?

Also, in the \_/ design, does the angles of the edges matter? How wide/narrow should the bends be?
The AH Supply reflector shape is better, but for a DIY effort is is much harder to do, because you then need to adjust 4 angles until you get the best shape, while the \_/ design only requires adjusting 2 angles, which is very easy. See Greystoke's post, https://www.plantedtank.net/forums/sh...ight=reflector for a thorough discussion of how to arrive at the optimum design without all the experimenting.

I found that even with a limited space to fit a reflector, it is possible to get a big improvement with the \_/ shape, and for most DIY light improvements, we don't need to find the best possible shape, just something that achieves a good result.

Hoppy
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post #12 of 13 (permalink) Old 02-21-2014, 03:03 PM
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Quote:
Originally Posted by Zoombie View Post
I have read (on these forums) that aluminum foil doesn't do well as a reflector. You could try some Mylar from a hydroponics store, it is quite reflective and intended for maximizing light.
If you want to shave using your reflector, mylar is by far the best choice. But, if you just want to get more light from the bulb you are using, aluminum foil is at least as good as mylar, if not better. The mylar that reflects is aluminum coated mylar, so it still aluminum doing the reflecting. The mylar just keeps it flat, supports it, and makes it easy to work with. But, it also absorbs some of the reflected light, and many aluminum coated mylar materials have such a thin layer of aluminum that some light passes through instead of being reflected.

Hoppy
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post #13 of 13 (permalink) Old 02-21-2014, 11:52 PM
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Hoppy>

Thanks, I wasn't thinking that one through entirely.

I think I was thinking about reflectors used for flashlights, where you do want closer to a parallel beam.
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