Henry Hatch

I have a 20 gallon tank with a cheapo light fixture that has a white plastic reflector. I'm planning to line the fixture with 2mm thick mylar. What is the best way to attach the mylar ? Should I use tape or glue ? I'm concerned about melting adhesive or having it catch fire. If this works I may try it on a fixture with an aluminum reflector, but I don't want the reflector to be ruined if I decide to take out the mylar.

Henry

cah925

I used a spray enamel for use on metal or wood that I bought from Home Depot. Spray on a lot the first time so you don't have to fix it later. Lay the mylar down and use a credit card or sqeegee to push the air out. I let mine dry overnight, but the instructions say 10-15 minutes. After that, just cut off the excess and install the light. I used this on 2 shop lights about 3 months ago and so far it has worked great.

SPC

I used Mylar with a VHO hood 7 or 8 years ago. If I remember corectly I used a double sided high temperature tape that I purchased from a heat and air supplier. I do remember, however, that the mylar began to fall apart at about the 2 year mark.

Steve

dansbdk

You can also try a spray adhesive available anywhere.
And the Mylar can be removed, and repositioned before the adhesive completely dries if you make a mistake! it's non-flamable after it drys, and the adhesive can be removed with GooGone, if you decide you don't like the Mylar!
Good luck!
Dan in Va

pinantanjohn

Actually it sounds counterintuitive and I didn't believe it when I heard it, but flat white paint is better for reflectors than mylar, especially close to the bulb. I used to grow plants hydroponically indoors under sodium lights and I tried everything including mylar. I got the best growth and most even lighting with flat white paint. Mylar can create "hot spots" in the growing area and can focus a lot of energy right back into the lamp with a reflector that wraps around the bulb. Not really dangerous with flouros but can kill HID's really fast.
To get the most "bang for the buck", try white paint.

Peace...
John

hoppycalif

Whether white paint is a better reflector or not depends on what you are trying to do with the reflector. White paint gives diffuse reflection - it reflects each "ray" of light in all directions, not just one. You can't aim a white painted reflector to direct the light into the tank. Much of the light will be reflected sideways, to strike the reflector in another location, where much will again be reflected sideways, etc. If the reflector is just the flat surface behind the light bulbs, white paint is probably better than mylar. But, if the reflector is a curved reflector behind each bulb, intended to redirect that light striking it towards the water, mylar is much better. Note that the expensive T5 fixtures all use polished aluminum reflectors, not white paint.

dgphelps

I've seen a few DIY projects using mirrors behind the bulbs... Any thoughts on that as opposed to mylar, aluminum or white paint?

hoppycalif

Since I posted my comment above I have done some testing and, to my surprise, good bright white paint is a very good reflector. Plain aluminum foil is also a good reflector. Mylar isn't as good as either of those. Glass mirrors, with the aluminizing on the back surface of the glass would be worse than all of the three above. Glass mirrors are very good for reflecting a true image of what you want to see, but not good at all at reflecting almost all of the incident light on the mirror. Front surface mirrors, like are used in astronomy telescopes, would be excellent reflectors, but protecting the very thin coating of aluminum without reducing the amount of light reflected would be a problem.

Any new light fixture I make I will probably use the brightest, most glaring white paint I can get as the reflective surface.

xdoomsongx

I use plain aluminum foil on the fixtures that I would like to get a little extra from. I stick it on with double sided tape. I have one tank that I have had this on for the past two years with no problems. I am not growing plants in said tank mind you, just wanted it to be a bit brighter. I have been very pleased with the results. The last DIY fixture I made I used high gloss white paint, and it is almost painful to look in the fixture with the light on, I think it works very well for reflection, but as of now, I have not gotten a chance to plant the tank. Look forward to seeing how it does.

hoppycalif

Here is some interesting information I found by an hour of googling:
www.usu.edu/cpl/PDF/Barium_Sulfate.pdf, which discusses making a high reflectivity white paint by mixing barium sulfate into latex paint. A cheap source of barium sulfate powder is http://www.sciencestuff.com/prod/Chem-Rgnts/C1296. I have bookmarked this site in case I decide to make a new light fixture sometime.