SE vs DE UV protection issues

[rtwodtwo99]

I was told that SE lights do not need protection from UV. Is that correct? I'm debating between SE and DE. I'm replacing my canopy and I'm placing a glass to remove and or clean under the lights to protect them from the waterand from UV.


I would like to know what is the proper distance the glass should be from the MH? What is the MIN and MAX distance the glass should be from the bulb. I'm going to use 2 x 250 W MH.
Any ideas were I can find some info? Thank You!

[tangwang]

Double ended bulbs need to be shielded with UV glas. Mogul base bulbs are already shielded. Do a bit of reading on the various differences between the two, and decide which one will suit your needs better...


matt

[pavster]

It depends on what kind of UV you are talking about. UV is lumped into three categories: UVC, UVB, and UVA. UVC is the killer stuff that is used in UV sterilizers, UVB and UVA are less harmful although they both cause sunburn and cancer in humans.

Glass is a good shield for UVC, poor for UVB, and useless for UVA.

An SE bulb has a glass envelope around its highly UVC/B/A emittant core; a DE bulb does not. You must shield a DE bulb to avoid major eye/skin/coral damage. In either case, you will still have a portion of UVA and UVB escaping the fixture. Some say this is good for corals; some say it's bad. It's not great for you, but light will pass through so much other stuff (water, aquarium glass/acrylic) that it's no concern.

Plastics are much better at shielding all UV, so if you want the ultimate filter, use Lexan or some such.

There is a fair amount of info re: all this on the web.

-pavel.

[pavster]

As far as the MAX and MIN distance, logic suggests that there is no such thing as MAX distance as long as no light escapes around the glass shield. As far as MIN distance, just look at dimensions of various DE pendants - they all have glass - probably as close as is safely possibly to reduce their manufacturing cost.

-pavel.

[45commando]

I'm just going back to my high school Biology here,but I thought glass was the BEST filter against UV rays?That is why you can sit all day in a glass made greenhouse & not get sunburn,you may die of heatstroke,but you won't have a suntan.I was taught that plastics allow UV rays through,but I'll stand corrected here.

[justin-branam]

as far as which is better i dont know. i do know however that if you use plastic as opposed to glass, it will get very hot and burn, giving it a yellow tint which will make your tank have a yellow tint on it. i use glass for mine.

[pavster]

You will in fact get sunburn in a glass greenhouse. The data I have seen showed that glass passes about 80% UVA, 40% UVB, and 0% UVC. Lexan is close to 0% for all three. The reason why plastic turns yellow over time is that it absorbs UV and becomes damaged by it.

Of course there might be glass specifically made to block all UV; I am not aware of such glass.

-pavel.

[artis]

The best recommendation is to read and satisfy yourself what's safe. Seems I recall that the DE fixtures tend to come in pendants or similar enclosure with UV resistant glass in place as part of a fixture.

The protective glass in SE bulbs comes as part of the bulb itself. These supposedly do not need additional UV shielding. Before using glass as a cover, you may want to read over advice the really experienced folks offer on the topic. You'll have some diminished light intensity and heating issues to consider. Some recommend egg crate as an alternative to glass.

[rtwodtwo99]

Thank you for your help.
So if I go wiith SE I will not need the protection. Wouldn't egg crate block a lot of the light?

[artis]

I find there is some minor shading if one's view is not directly under the MH bulb. My pardon if you are familiar with egg crate, but a brief description might help.

The term "egg crate" is a slang reference to a product used as a cover for florescent lights. Essentially its a plastic lattice of open squares, roughly .5" - 1.0" on a side. Thickness is about .5 inch or less. Directly under the light, there is no blockage at all and the light simply travels through open air. At angle, you do find some shadowing as a result of the thickness of the egg crate. I do not have sufficient experience to say whether that amount of shadowing is detrimental to livestock for a particular wattage. A more experienced reefer or few would need to advise on that.

I'd recommend doing a site search on egg crate. You should find a number of references and likely some pictures. I've bought several sheets at Lowes and it could be available from other locations as well.