I did some reflectors for some freshwater planted tanks a bit ago. I was making them to maximize the light getting to the tank with screw in spiral bulbs by directing light and minimizing restrike. The same principle applies to all light reflector/bulb combos. This MAY be useful to you if you can translate it to your system.
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Importance of a Good Reflector
by Tony Gomez
If you are going to put down some cold hard cash on a lighting system, you want to get your money's worth...right? The Key to maximizing your lighting is with a well designed reflector. A good reflector is composed of two things: 1) A highly reflective material 2) A proper shape.
Being the cheap guy that I am, I wanted to do a DIY light setup using a DIY reflector and some inexpensive spiral compact bulbs that I found at homedepot (2x 19watt 6500K). The first challenge was to come up with a reflector geometry that solved the problem with large cross section bulbs--restrike (reflected light bouncing back onto the bulb). I solved this problem by using "spider reflector" geometry. The math to solve for the geometry is simple. The angle of incidence= the angle of reflectance.

Using this, I optimized (could be better, but this is plenty good) a reflector design that is SPECIFIC to my bulb diameter. I also designed it such that I get a good spread of light into the tank and not a focused spot.


The next Challenge wasn't really a big challenge. I needed a highly reflective material so I purchased some polished aluminum sheeting from www.mcmaster.com. This isn't as good as specular aluminum, but it was good enough.
After building the reflector (I had access to a metal folder, so making the angles wasn't hard) I wanted to show myself that my time was not wasted, so I shot a series of comparison shots. Unfortunately, I did not use Aluminum foil in the comparison photo shoot, but I assure you that white paint is much better than aluminum foil. AF works better as a diffuser than a reflector. Mylar sheeting, however is a good reflector.
Guide to the pictures below:
Top picture is to the side of the tank
Bottom picture is in the center of the tank
From Left to right:
DIY reflector with side panels
DIY Reflector
High brightness white paper reflector (a proxy for paint)
No reflector
No hood or reflector

Hopefully the images speak for themselves.
I know some of you won't want to do a DIY reflector to save money, so I will plug a light source. www.ahsupply.com has IMO the best reflector design for those who can handle a screw driver. I personally own 3 of their kits.
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