You know you make an excellent point... hmm... let me run it by my wife... I'm sure she wouldnt have a problem with it  

Not that you need a nicer tank...

From Sarnacks link above:

Only reference I have right now is original "Korallrevs akvariet" by Foss� & Nilsen, vol 1. On page 46 there is a table that references OSRAM databook and it clearly shows that HQI lamps produce all types of UV radiation (A-C).

HQI 250W (at 1000 lumens):
UV-C 29 mW/m2
UV-B 108 mW/m2
UV-A 900 mW/m2

And from the http://www.srrb.noaa.gov/UV/ - http://www.srrb.noaa.gov/UV/  website:

UV wavelengths, particularly

those associated with UVB, are able to efficiently break DNA bonds. While UV,

particularly UVA, can assist in repairing DNA damage, the primary effect of UV appears

to be damaging to both DNA and individual cells.

I'm pretty sure Sarnack is right.  Quartz glass is used due to the very high temperature generated at the arc (regular glass would melt).  I think you're a bit crazy to operate double ended MH bulbs without a piece of glass between the bulb and your eyes/skin/ect.  Just my opinion.

Marcus wrote: What's protecting the corals from this UV light?

This is a great question.  There are some very highly paid (we're talking millions here) people who are trying to find this out.  It is big big for cancer.  I don't have many answers but I do know some.  One thing is that the UV light actually does NOT penetrate as far as blue light.  Hard to believe but true.  The other item to note is that the water greatly absorbs (or disperses) the UV and is what protects the corals.  Also, corals near the surface slime coat themselves for protection.

But the big answer (again hard to believe) is that nothing is protecting the corals.  That is why they die.  Many coral experts think that corals would be growing at astonishing rates if there wasn't UV light.  It is hypothesised, and somewhat tested, that many corals are limited on how high up the water column they can grow simply because they are limited by UV. 

I think any liquid (if I remember correctly) will shield UV.  That is why a piece of glass is so important, it uses its liquid properties to shield UV and I'm convinced it works.

Adam

Marcus wrote: Adam, so you are saying that an acro that is 4" below the surface of the water will NOT be affected by UV because the water will protect it?

Oh no, just the opposite, I think it will be highly affected, which is why they don't naturally grow (well some do) that close to the water surface.  I think UV naturally is a huge threat to corals.  However at something like 30 feet, yes that water will have protected it.  Where inbetween 4" and 30' do I think it makes the cut off.... I don't know.  I'll guess at 10 feet. 

Hmm, I wonder how much UV our halides give off, compared to natural sunlight, and for how many hours per day, and stuff like that.

Adam

wrong thread

Jon and Sarnack, so if I buy a piece of tempered 1/8" "safety glass", it'll shield the UV-B&C?

I think it would be sufficient.  The outer tube on a single socketed bulb is thinner then that and it supposedly works.

Sarnak, you're right on some stuff and wrong on a few others.

Annealling is what you discribed as tempering.

Tempering glass is done by slowly heating the glass up to annealing temperatures, where the glass just begins to get soft.  Then rapidly cooling just the outside by blasting cool air across the surface.  Then allow the rest to slowly cool.  This process leaves the surface in compression and interior in tension.

Pyrex, corning-ware, corelle, vicor, ect are all regular old soda lime glass that have some of the soda atoms either displaced or replaced with other atoms such as boron (Pyrex), potassium (Corelle), titanium dioxide (corning ware) and others.

You might be thinking about safety glass with a film incorporated into the glass.

Enough glass talk...

Marcus, all glass, tempered or not, will filter out UV.  The thicker the glass the more it will filter.  The fact that single ended MH bulbs have 1/16" glass outer bulbs seems to indicated that they (the manufacturers) feel that is sufficient.  The only glass that I'm aware of that is transparent to UV is quartz.  That is why many UV sterilizers have a quartz sleeve for the UV bulb to fit into.  UV radiation is a serious thing, if it were me, I would try to confirm this info with a bulb manufacture such as Philips or Panasonic.

jfinch wrote: And all glass other then quartz will filter harmful UV (B&C and most of the shorter wavelength A) as far as I know.

Jon,

I haven't studied p-waves and s-waves for a long time but I think you're correct.  I believe the difference is because quartz is actually a solid, unlike glass.

Adam

Wow Adam, you're stretching my memory thin.  I'm not really sure why quartz glass is transparent to UV.  But I think there's a difference between quartz mineral (crystal) and quartz glass (non crystal).  I'd like to know myself, maybe you could ask one of those smarty pants professers where you work?

Sarnack, I was just reading about doping of metal oxides on quartz glass to reduce it's UV transparency for use in HID light bulbs (the arc tube).  So you're right, metals are added to quartz glass to reduce it's UV transparency!

Marcus, I think it's the shape of the prizm that's important, not what it's made out of.  I think most are made from leaded glass because it has better optical qualities.

jfinch wrote: Wow Adam, you're stretching my memory thin.  I'm not really sure why quartz glass is transparent to UV.  But I think there's a difference between quartz mineral (crystal) and quartz glass (non crystal).

Yeah I was thinking that as well.  However, I think it is because the glass is a liquid, but the quartz glass is still a solid, even if it is not in a crystaline form. I'm stretching my memory here as well.

Adam

15 yrs ago, I never thought I'd need to remember anything from 2nd semester Physical Chemistry... Now I wish I'd have payed more attention .

Dave, you should post more!

This has been an informative thread for me!

jfinch wrote: Dave, you should post more!

I agree, everytime Dave posts something, I enjoy it.

Adam