How much light strength lost through acrylic

[mark0933]

OK, as the title says, how much light strength will I lose through 3/4" acrylic. Disregard heat issues, if I run a 400W MH what does it compare to vs an unobstructed view? I know you lose a lot of UV with a glass top, but never seen any data on through an acrylic panel.

Mark

[areze]

never seen a test on that. assuming the acrylic is clean, and you keep it from hazing from the heat. it should be relatively minimal as acrylic is 99.9% optically clear.

[dball711]

I have tested lumens with and with out acrylic shield with mixed results, 0 to 5% reduction with an acrylic shield. Depending on the acrylic (many different qualities available) I believe the light (lumens) reduction is minimal at best.

[mark0933]

Thank you both for replies, so if I am not worried about the heat and can mount the reflector high enough, then if I put 400W MH over the 36" tank most if not all will get to the bottom of the tank.

Mark

[gene@icecap]

Gentlemen:

I would advise against using acrylic with anything Metal Halide. The softening point for acylic is 99C and the melting point is 150C, in addition acylic is deisigned to filter out UV to prevent yellowing, this will inhibit growth. The tranmission loss rate is greater than 8% for sheet that is standard lighting sheet (the type found in a 2x4 ceiling fixture in an office or nominal .100") and losses increase as thickness does.

Use glass as it has better transmission and is easier to clean and can not melt...

Best!!

[painkiller1009]

Heres a link to Melevsreef were he puts a piece of 1/4in acrylic over a tank and measures par.
Melecsreef.com (http://www.melevsreef.com/par_readings.html)

[mark0933]

<a href=showthread.php?s=&postid=13449195#post13449195 target=_blank>Originally posted</a> by gene@icecap
Gentlemen:

I would advise against using acrylic with anything Metal Halide. The softening point for acylic is 99C and the melting point is 150C, in addition acylic is deisigned to filter out UV to prevent yellowing, this will inhibit growth. The tranmission loss rate is greater than 8% for sheet that is standard lighting sheet (the type found in a 2x4 ceiling fixture in an office or nominal .100") and losses increase as thickness does.

Use glass as it has better transmission and is easier to clean and can not melt...

Best!!

OK, I am not planning on using acrylic as the shield directly under the bulb, as I know it will melt (even I am not that stupid).

I also can't change the brace to glass as you suggested , my tank has a complete cover with access holes cut out of it (but still has about a 12" brace down the middle in both directions)

Mark

[mark0933]

This is what I am dealing with:

http://i101.photobucket.com/albums/m75/mark0933/P9280250.jpg

Mark

[gene@icecap]

Metal Halide is a point source (lighting type) so if the reflectors and lamps are directed through the openings, they will work perfectly and you should have no issues. I would encourage 12 inches space above the acrylic to allow for venting and perhaps a couple of fans to encourage movement. At that height using unshielded "spider type" reflectors would work very well. That is what Dr. Joshi uses over his tank with our ballasts.

[Untamed12]

Yup....you have four holes and perfect spot to put four MH lights. Don't put any MH over any of the acrylic braces. Just don't.