# best parabolic reflectors for T8 bulbs



## fishstein (Dec 12, 2005)

I'm looking for some good parabolic reflectors to install in my DIY hood. Can anyone recommend good ones for individual bulbs? My bulbs are 48". Currently I have white latex paint on the inside of the oak-stained wood hood of my tank, which works quite well. Good curved reflectors for each bulb, whether polished aluminum or white gloss, would help push even more light into the tank without adding more bulbs (I still have room for more bulbs, but I'm quite sure reflectors will increase my brightness to where I want it).

Thanks,

Fishstein


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## SnakeIce (May 9, 2005)

The only reflectors I've come across are for t5, which hardly helps those that don't use that size bulb. 

Have you thought about useing a graphing machine to come up with a parabolic shape in the family of y=x^2? To find a focal length that will work with the diameter bulbs you have use this to find the scalar to put in front of the x^2, 1/(focal length)^2. The further you put the bulb away from the bottom of the parabola the more efficient it will, but it will also take up more horizontal space. The focal length is the distance from the bottom of the parabola to the center of the bulb that is the spot that best directs the light in the direction you desire. Change the focal length and the shape of the parabola changes to maintain a shape that will direct the most light downward.

Once you have the graph use them to make supports with a jig saw or band saw that would hold the thin panel bent to the shape of the parabola. Then a veneer of highly reflective material would finish that diy job off.

y=(1/(focal length)^2)x^2


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## Laith (Sep 4, 2004)

www.ahsupply.com apparently has some of the best reflectors available:

http://ahsupply.com/mcart/index.cgi?code=3&cat=9

See if they fit your needs. I've never used them (I'm not in the US) but have only heard great things about them.


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## yoshikuni (Sep 19, 2005)

i dont mean to jack your thread fishstein, but snakeice, what kind of t5 reflectors do you have? and where did you get them?

i'm looking for some good t5 reflectors myself.


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## SnakeIce (May 9, 2005)

I don't have any parabolic reflectors at the moment, I've just had lots of time in the last 5 years I've been dreaming about the 75 gallon tank to look at various lighting options.

Sunlight supply has a reflector in their product list that looks to be parabolic.
http://www.sunlightsupply.com/aquarium/products/lighting_components.shtml#mag_rep_ballasts

Tec lights t5 retrofits come with a reflector and I think they can be bought separately.


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## hoppycalif (Apr 7, 2005)

Parabolic reflectors really aren't needed for this application, nor will they work well to give a parallel beam into the tank. Since all bulbs have considerable thickness, and are coated with phosphors which do the radiating, they are no where near a line source of light. Much easier to design and build is a reflector consisting of flat surfaces, much as AHS reflectors are. The goal is to catch the light from the back half of the bulb and re-direct it towards the tank, without it striking the bulb. You can check its effectiveness by looking at the reflector with the bulb installed and see if you see all surfaces of the bulb. Any light entering the tank at an angle even close to 90 degrees will be effective. A bigger problem is how to get a great reflective surface, one that reflects 90% of the light that hits it. Highly polished aluminum will do that, and very good quality aluminized mylar will come close.


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## fishstein (Dec 12, 2005)

Thanks very much for the good suggestions. I should have specified any good reflector. It needn't be parabolic. IMHO AH Supply have the best reflectors I've seen so far. I may adapt their 22" reflectors. 

2 22" reflectors may work better than a single 48" for me because I have a support beam running over the lights right in the middle of my hood which wouldn't allow easy installation of a single 48" long reflector. I very much believe in and enjoy DIY but I have very little free time these days to devote to a DIY project.


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## ruki (Jul 4, 2006)

of couple of thoughts

*PC bulbs and parabolic reflectors*
AHSupply uses Power Compact lamps for most (all?) of their reflectors. Parabolic reflectors make little sense for a non-linear bulbs. PC curve back against themselves and have light emitted from one side of the bend back across the gap and into the other side. This wastes light and warms the tube a bit. Generally a sucky situation for a reflector.

*Linear bulbs and parabolic reflectors*
With a linear tube, a pure parabolic reflector will still send some of the light back at the tube, wasting light and warming the tube again. Smaller tubs are better ( T5 vs T8 ) since they are smaller target, but still this wastes light.

Optimally, you want to have a parabolic shape for most of the reflector, except for the part directly above the bulb, that part as an inverted V shape. I believe this approach is what makes the TekLight reflector better than most.

Another thing consider is a light enclosure that acts as a heat sink for the bulb and/or ballast. That way you don't need to waste energy powering a fan to cool the fixture. The TekLight also does this.

TekLights are pricey, but a good DIYer should be able to make something similar with access to metal bending tools.


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## fsnow55 (Jul 30, 2006)

This might be silly, I don't know... How 'bout just flat mirrors pasted at the back? esp. since mirrors reflect light well. I have the same setup (white painted hood) and have the same problem (4 T8s for a 100g tank).


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## ruki (Jul 4, 2006)

fsnow55 said:


> This might be silly, I don't know... How 'bout just flat mirrors pasted at the back? esp. since mirrors reflect light well. I have the same setup (white painted hood) and have the same problem (4 T8s for a 100g tank).


That will work somewhat, but won't be optimal for sending light down into the tank. Do the angle of incidence thing with a cross section and see how much light gets sent straight down versus back at the tube. It takes time to come up with something close to optimal, so it might just good enough for practical purposes though.


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## hoppycalif (Apr 7, 2005)

With a piece of paper, straight edge and a protractor you can do a ray tracing experiment to design a good reflector shape made of flat mirrors. You only need to do it for half of the bulb/reflector. Just remember that a light ray will reflect off at the same angle that it strikes the mirror. And, assume all of the light is emitted at a right angle to the surface of the bulb. I have spent many hours playing with this!!


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