what is the effect of acrylic on light penetration?

[orionsmamma]

I just got a second set of lights, and they came with an acrylic "shield". I have not been using it on my current lights, but I get a ton of salt build up on them. The lights are sitting right on top of the tank, and the splash from my skimmer is what is causing it. It would be easier for me to clean it off of the shield, but I dont want to effect how much light is getting to my corals. The shield is super thin, mabey 1/8 of an inch.

TIA!

[javajaws]

Generally I think acrylic lets through 98-99% of light that passes through it. But it's not the chemical properties of acrylic that you have to worry about - it's that danged salt buildup and the long term clarity of the material from scratching, etc.

What kind of lights are these are what are you keeping livestock wise under them?

[bertoni]

I think the acrylic can take up to 10% of the light, but as stated previously, the buildup is worse. You can find more data by looking at sites that discuss StarFire tanks.

The downside of removing the shield is that the bulbs and their connections get the spray. I'd worry about the connections not necessarily being waterproof. I always keep an acrylic shield in place for this reason. Some manufacturers do use waterproof connectors, though. What kind of fixture do you have?

[WaterKeeper]

My guess is that you are using fluorescent as you have your lights right on the tank. Acrylic is fine for those as it does allow good light passage. It is a different story for some HQI double ended bulbs. The acrylic in that case not only lets light pass but UV radiation. It can be harmful to your tank and possibly your own eyes. If the bulbs you have are unshielded and emit UV use glass instead. It allows almost as much light to pass but blocks harmful UV. Check with the bulb manufacturer if you are unsure.

[orionsmamma]

I have 2 Jebo PC fixtures, that each hold 2 55 watt bulbs (for a total of 220 watts). I only have one of these fixtures on the tank, and recieved the second today. I am currently keeping a open brain coral, candy cane, torch and xenia.

As far as critters, I have a myriad of snails, 1 hawaiian feather duster, 1 cleaner shrimp, 2 peppermint shrimp, 1 LM blenny, 1 clown goby, 1 blue green chromis, many bristle worms and a zillion "pods" :D

The reason I want to use the shield is to prevent the salt from getting on the bulbs and reflectors. The reflector on the fixture that is on the tank now is starting to show signs of rust. It would be easier to clean the shield than the bulbs. I'm gonna throw them on there if they really do let most of the light in.

I do plan on getting a hood on the tank soon to eliminate this problem completely.

Thanks!
Donna

[bertoni]

I'd definitely add the plastic shield in your case. Rust on the reflector is bad, and you could be rusting the connectors for the bulbs, etc., as well. I've measured the light loss as less than 1/3 stop, in photographic terms, so I don't think it's significant in most cases.

If you really want more light, go MH or add more PC bulbs. :)

[WaterKeeper]

Originally posted by bertoni
Rust on the reflector is bad,
lol: John,

Don't you hate it when aluminum rusts.

[orionsmamma]

Originally posted by bertoni


If you really want more light, go MH or add more PC bulbs. :)

Thats what I'm trying to do :D

I only have a 30 gal tank right now. Soon, I plan on moving it over to a 40 breeder...I love the look of the shorter/wider tanks. 220 watts on a 30 is 7.3 watts per gallon, and on a 40 is 5.5 Isnt this fairly good?

[WaterKeeper]

It is about average. You can keep most critters with around 6 wpg, especially on a shallow tank. Some things like clams, some anemones and SPS coral need more in the range of 8 wpg or better.