[Ninong]

A couple of points: Does anyone know whether regular tempered glass absorbs ANY amount of UV radiation? I have read that it does but I cannot find the reference and I am not sure one way or the other.

I have also read that the HQI DE lamps put out a "certain amount" of UV-C, a "certain amount" of UV-B and a substantial amount of UV-A.

It is my understanding that "any amount" of UV-C can be deadly, exposure to UV-B can be damaging long term and UV-A, in general, is no big deal.

It is also my understanding that no UV-C reaches Earth's surface as it is all absorbed by the atomosphere. Therefore, exposure to unshielded HQI DE lamps cannot be compared to exposure to the sun.

Ninong

[Ninong]

Originally posted by PerryinCA:
I remember Richard Harker....or was is Dana Riddle?....anyway, one of them posted the UV levels of tropical sunlight vs. that of a couple MH lamps a long while back on hte compuserve board, and the sun completely put the others to shame.

"However, under certain conditions (high wattage, reflector material with high UV reflectance, etc.), it is possible for UV-A radiation levels at the bottom of an aquarium to exceed UV found at the ocean’s surface."--Dana Riddle

Originally posted by PerryinCA:
Although the HQI puts out small amounts of UV-C, I doubt that it'd be enough to do alot of damage.

"The third UV category consists of wavelengths between 200 and 280 nm and is referred to as UV-C. The Earth’s atmosphere absorbs UV-C produced by the sun and therefore is not found naturally. However, UV-C can be produced by artificial means."--Dana Riddle

Originally posted by Ltspd:
...that has no other properties for UV reduction than standard glass. The temparing only covers the heat issue. I think...

"Transmission Properties (Percentage) of Regular Soda-Lime Glass 3/16" thickness: PAR=91%, UV-A=73%, UV-B=3%"--Dana Riddle

That is interesting because he also tested what he called "Unknown Plastic" of 3/16" thickness from a Giesemann fixture and got these measurements: PAR=92%, UV-A=85%, UV-B=35%.

What I find interesting is the fact that the regular glass transmitted approximately the same percentage of PAR, but the regular glass was a little better at absorbing UV-A (73% vs. 85%), and the really interesting figure is the fact that regular glass transmitted only 3% of UV-B vs. 35% for the 3/16" thick "Unknown Plastic."

So, based on Dana Riddle's testing, it appears that regular glass does absorb about 27% of UV-A and 97% of UV-B. He didn't test for UV-C. Perhaps that is why AB-Aqualine uses regular glass in their fixtures. This regular glass is then tempered so that it will be more heat resistant.

Ninong

Ref for above: http://www.aquarium-design.com/reef/uvlighting.html

P.S. -- Another material that Dana tested was AtoHaus UF-3** 3/16" thick. This has special UV-absorbing properties. It transmitted 90% PAR, only 5% UV-A, and less than 1% UV-B.

[Ltspd]

Ninong,

Like I need another mission, I contacte Ushio this afternoon in regards to what the bulbs emitt. I was told, that both the double ended and the mogual aquarium bulbs emit UV rays. I asked for a spec sheet either emailed or faxed. Hopefully I will get something. I will also contact Schott once again and get some real data that I can lay my hands on.

I have a spec sheet on glass right here in front of me. Its been faxed to me, the last time we discussed this issue. Its hard to read, but I found this link which has the same info. Its based on 1/4" which is less pass thru light (1%) and more UV absorbtion (3%)

http://www.viracon.com/info/performa...le&glasstype=2


Here is a link on tempering.
http://www.glassonweb.com/glassmanua...x/tempered.htm

That may also have some good info on specs.

[Ninong]

Paul,

The last time we discussed UV radiation and whether or not UV-absorbing shielding was a good idea or not, I took the position that it was "a good idea" with all metal halide lamps and a "requirement" with double-ended lamps. I pointed out the recommendations of several authors that agreed with that conclusion. I even referenced the same Dana Riddle article that measured UV radiation transmitted by VHO fluorescent lamps and mogul base metal halide lamps with protective glass outer envelopes. Mr. Riddle's recommendation, based on his testing, is that all metal halide lamps put out a certain amount of UV radiation and therefore, all metal halide lamps should be shielded with an additional UV-absorbing shield of some kind.

If you remember, several members disagreed with my take on that topic and posted the question to Eric Borneman. I gave up "discussing" the point with Eric in his forum after he finally agreed that it was probably a good idea to use a shield for HQI DE lamps to protect them from splashing water. He never did agree that it was necessary from a UV radiation standpoint.

It may be that several members on this board still hold that same opinion: That it is not really necessary to shield HQI DE lamps. Obviously Perry thinks that and if I am reading your posts correctly, I believe that you feel that the only reason for shielding HQI DE lamps is to protect them from splashing.

Ninong

[Ninong]

Originally posted by Ltspd:
Like I need another mission, I contacte Ushio this afternoon in regards to what the bulbs emitt. I was told, that both the double ended and the mogual aquarium bulbs emit UV rays.

Paul, this is nothing new. We discussed this ad nauseam in the last UV thread. The only difference, as I pointed out previously, is that the double-ended lamps actually produce a small amount of UV-C vs. none for mogul base metal halides and more UV-B vs. mogul base lamps. You can find all of the measurements in the same Dana Riddle article that I linked above and which I linked in my posts in the earlier UV shielding thread. I doubt that many people bothered to read the entire article. I also posted references to several other sources who recommended shielding ALL metal halide lamps. That is a position that is not common practice in the hobby from what I can tell based on the various bulletin board members' tanks.

We don't have to reinvent the wheel. You, and many others, discussed with Eric Borneman whether HQI DE lamps required shielding and Eric originally said "no they do not." That seemed to satisfy most of the people in that thread. I pushed the point with Eric and he finally posted "sigh..." and agreed that it was probably a good idea to use a shield but only to prevent splashing water from causing the lamps to explode.

Ninong

[Ltspd]

NO I agree 110% that they ALL need some form of shield. The problem I have is that everyone is refering to the special UV glass used on purchased fixtures. That special UV glass is nothing more than tempared float glass. The same glass I am using on my DIY setup and the same glass I saw in person at a trip to a reef shop a hour or so away. Its the same fixture you are using.

I am just trying to prove or disprove the myth of the UV rays from these and standard bulbs. IMO, it would be money well spent on some research from someone of noted authority such as Sanjay. If I could find the equipement to test bulbs for the 3 types of UV I would, and post them for all to see.

This got started due to the comment that was made about this is what happens without the UV shield, and both you and I know it had nothing to do with UV, but mere stupidity on the user.

I agreed with Eric on the lack of UV protection requied for corals. As he pointed out, if I remember correctly, is that they are not shielded from UV in the wild. What makes our tanks diffrent for the same speicies. Now, we need to take precautions to provide safe viewing and working means for ourselves.

[Ninong]

Paul,

OK, at least you and I both now know that regular tempered glass does absorb 27% of UV-A and 97% of UV-B based on Dana Riddle's testing. Evidentally some manufacturers do use "special" UV-absorbing shielding such as AtoHaus UF-3 plastic, but AB-Aqualine uses UV-absorbing regular tempered glass... nothing special about that but it does absorb most of the UV radiation.

Ninong

P.S. -- And it goes without saying that I am still convinced that unshielded HQI DE lamps would do considerable damage to corals in aquaria, especially those corals that are found at depths below 10 meters.

[Ltspd]

Originally posted by Ninong

P.S. -- And it goes without saying that I am still convinced that unshielded HQI DE lamps would do considerable damage to corals in aquaria, especially those corals that are found at depths below 10 meters.

Why only these bulbs? Would not the assumption be made for ALL bulbs? Its my understanding that a lot of standard mogul socket bulbs do not have the borasilicate coating. Or atleast I have been led to beleive that from Ushio.

[Ninong]

Because regular mogul base lamps have an outer glass envelope that does absorb some UV radiation. My understanding is that this glass is a special borosilicate glass, not that it has any special coatings. In fact, Ushio calls it "UV-absorbing quartz glass." (And the last time you talked to someone at Ushio, he was not familiar with his company's website.)

In any case, all of the literature that warns about the HQI DE lamps points out that they transmit more UV radiation than mogul base lamps that have outer glass envelopes. Also, many authors make a point of the fact that HQI DE lamps transmit a certain amount of UV-C vs. no UV-C for mogul base lamps.

That's why. Also, all of the manufacturers of HQI DE lamps warn that they should never be operated without a "protective" shield in place. And the manufacturer of my fixture, AB-Aqualine, warns that the fixture must never be operated without the "protective shield" in place.

Ninong

P.S. -- You know, all of this is explained in detail in Dana Riddle's article on UV radiation. He gives the exact transmission measurements for UV radiation of mogul base metal halide lamps. He also gives several references from the scientific literature documenting the harmful effects of excessive UV radiation on certain corals.

[Ninong]

Hey, while we're on the subject of metal halides, I just checked Richard Harker's "Nipple Nonsense" thread: http://reefcentral.com/vbulletin/sho...threadid=60888 and it looks like no one is responding to the questions I raised in my post two days ago. Looks like I kinda killed the thread.

Ninong

P.S. -- Why don't you go over there and bump it up.

[Ltspd]

Hey I am at my quota for thread bumping this week. The last thread bumping has cost me 200 and a headache,

[bowfront]

Originally posted by Ltspd
NO
This got started due to the comment that was made about this is what happens without the UV shield, and both you and I know it had nothing to do with UV, but mere stupidity on the user.

What exactly do you mean that it had nothing to do with UV? The poster placed an unshielded HQI DE pendant over his tank for 3 hours and successfully fried a fish. I never implied the problems in his tank were due to a temperature spike. I firmly believe that UV exposure killed the fish and would have continued to kill his corals if left unchecked. I've read other horror stories on RC with the same scenario. I've also read this thread where Eric Borneman goes way out on a limb with you guys. I respect his work but don't buy into any of his arguments there. Let's say that you could acclimate aquarium corals to UV exposure levels equal to an unshielded DE bulb what's the sense? Is additional UV needed to successfully grow high light corals? You tell me. Even if it helps is it worth the extra health concerns to the normal reef keeper? Don't get me wrong I respect all of the basically pioneer work that you have done with DIY HQI lighting. I think threads like this one cover a number of bases and that's a good thing for everyone. Ninong you make some strong points as usual.

[Ltspd]

bowfront, please dont take it the wrong way. I get sort of bent when all these folks think that that pc of glass between them and the double ended bulbs are some sort of magic bean that is doing all kinds of protection. Its not, and as both Ninong and I agree upon, you need this pc of glass shiled for all mh bulbs.

I think this same situation would have happened with a Iwaskai 250w bulb or any 250w bulb in the same location. Once again stupidity or lack of knowledge played the role.

Please understand that this is my personal opinion based on my research and investigations, its your opinion based on your research in regards to the UV issues. Please feel free to share some of your data as you uncover it so we can all benifit from all the stuff we uncover. I plan on calling Schott once again and seeing if I can get good data faxed or emailed to me to share.

[Ltspd]

Originally posted by Ninong
P.S. -- You know, all of this is explained in detail in Dana Riddle's article on UV radiation. He gives the exact transmission measurements for UV radiation of mogul base metal halide lamps. He also gives several references from the scientific literature documenting the harmful effects of excessive UV radiation on certain corals.

You know I had this article printed out, but it was from over 1 year ago. I remember some of the data and information but need to re-read again. I brought it into the office today, things should be quiet and I can re-read it later in the morning. If I remember this article is about 5 years old correct? Any new data out there?

[Ninong]

Paul,

I'm not sure when Dana wrote that UV article. I can't seem to find his website right now. Anyway, here are links to a few other articles he wrote that came up when I ran a search on Riddle Aquatic Laboratories: http://search.msn.com/results.asp?q=...thr=&x=31&y=13

Ninong

[Ltspd]

Some thoughts on the article:

To recap what we already know.

UV-A is the least harmful to us.

UV-B is our concern

UV-C is absorbed by earth, but what in out tank absorbs this? if any?

Now, the authors graphs show only UV-A, the least of our concern. He does supply UV-B on 3 bulbs, Iwasaki, coralife, Radium all standard outer cased bulbs. Each bulb allows around the 60% of UV-B, and 80=% of UV-A.

The AB 10kk, 175w bulbs are tested and the levels are measured in their approipate outputs. What level of UV-B is acceptable? In microeinstien's. We are told that we have outputs of UV-B but is that level bad? If I remember this was brought up in a old discussion and I dont remember if it was answered.

No double ended bulbs were tested? We are told they produce more UV's. I wonder if this is becasue they dont have the outer casing

The author tells us that Mirrored reflectors are the best/worst for reflective quality of UV's. One can assume its also good for the stuff we want.

We are told UV penetrates natural seawater in the wild.

Corals have means to protect themselves.

We are told that all bulbs produce bad UV, and the outer shell only weakens it's rays, they do not take it completly away.

We are also told that "green" glass (standard glass) allows 73% pass thru of UV-A and less than 1% of UV-B. Now, all the glass data I have generilizes the UV transmittance http://www.viracon.com/info/performa...stype=2&font=1

Now, does the standard tempared glass provide enough reduction? We dont know for sure with out further breakdown of the UV rays. One could say that it does, or according to the author's results.

Now, does this prove or disprove the thread on UV's and the guys 26g tank? Depends which side of the coin you look at. Yes, we all agree he needed the "shield", but IMO everybody needs the "shield" regardless of the bulb used. Did the UV's cause his fish to die? Could it have been the sudden shock of bright light? Here again we have our opinions.

I will still say this.

The glass under your store bought fixtures are nothing special. They are not the magic bean or kroptonite shield they are made out to be, the are a pc of tempared float glass in my opinion.

[Ninong]

Originally posted by Ltspd:

UV-A is the least harmful to us.

True. In fact, some UV-A is beneficial to all living things.

UV-B is our concern

True. Too much UV-B is harmful to all living things. It causes sunburn and skin cancer in H. sapiens for example.

UV-C is absorbed by earth, but what in out tank absorbs this? if any?

Nothing absorbs it in your tank. It's not supposed to be introduced into your tank in the first place. Any amount of UV-C is potentially deadly. UV-C irradiation is what makes UV sterilizers work. As far as I know, only double-ended metal halide lamps produce any amount of UV-C. You may want to research that further, but I have never seen UV-C measurements from mogul base metal halide lamps.

What level of UV-B is acceptable?

Depends. If you are talking about humans, excessive UV-B will cause sunburn and long term exposure to excessive UV-B will cause melanoma. Excessive UV-B could cause problems for certain corals but in nature most of them adapt to natural levels of UV-B over time. Remember, they are not exposed to UV-C in nature because all of it is absorbed by the atomosphere. Also, don't forget that it takes corals two to three weeks in nature to complete the adaptation process to sustained changes in light levels. They are already adapted to natural diurnal light cycles and modify their photosynethsis processes on a daily basis to adjust to differences between high noon light intensity and light intensity at other times of the day.

In microeinstien's.

You would have to look that up in the scientific literature. Dana Riddle gave several references in his article that you just printed out.

We are told that we have outputs of UV-B but is that level bad? If I remember this was brought up in a old discussion and I dont remember if it was answered.

Eric answered that question by saying that most corals are capable of adapting to varying natural light conditions in the wild. At one point he acknowledged that any amount of UV-C would be extremely detrimental to the inhabitants of the tank and the inhabitants of the house. Don't forget that Eric is talking about natural levels and Dana says that it is sometimes possible to exceed natural levels of UV radiation with high wattage metal halides and efficient reflectors.

No double ended bulbs were tested?

They are almost never tested in U.S. hobby literature because they are not in common use here.

We are told they produce more UV's. I wonder if this is becasue they dont have the outer casing

Of course it is, but it could also be due to other differences between double-ended and single-ended lamps.

The author tells us that Mirrored reflectors are the best/worst for reflective quality of UV's.

There are two ways of looking at the reflector issue: (1) A high quality reflector like a Spider-lite will concentrate and intensify the light, giving you the most bang for your lamp buck, and (2) Maybe a more diffuse reflector material, such as the dimpled aluminum or even a plain white reflector would be better in certain situations. You would not have as much intensity but you would not have to worry about any hot spots either.

One can assume its also good for the stuff we want.

Depends on what you want. If you put 400w 6500K Iwasaki lamps in a Spider-lite reflector over a tank that is only 20" tall (meaning the water column is maybe 15"), you will have no problems with SPS but you will have a hard time finding lower light areas in the tank. You would have to be very careful in acclimating some soft corals to such intense lighting.

We are told UV penetrates natural seawater in the wild.

Yes, but it doesn't penetrate at the same intensity as it gets deeper. That's why deeper corals cannot adapt to UV as readily as shallow water corals. Also, ultraviolet and violet wavelengths fall off rapidly as you get into deeper water. All you have left below 30 meters depth is blue and green (450-550nm).

Corals have means to protect themselves.

Within reason. They have protective pigments and they can adjust their photosynthetic processes by varying the population and even the size of their zooxanthellae. Actually the individual zooxanthella have the ability to enlarge the size of their PSU (photosynthesis units)--the protein-pigment complexes which absorb light energy and transfer it to the reaction centers of photosynthesis I and II. The average size of PSU in corals adapted to low light is 1.5 times greater than in corals living in normal light. The best example of that is the fact that some Acropora are capable of maintaining the same rate of photosynthesis over a range from 1 meter to 30 meters depth. The light at 1 meter is 85% of PARS (photosynthetically active ratiation at the surface) and the light at 30 meters is only 8.5% of PARS.

We are told that all bulbs produce bad UV, and the outer shell only weakens it's rays, they do not take it completly away.

That is the thrust of the argument made by Dana Riddle and others who recommend using an additional shield even for regular mogul base metal halide lamps that have a protective outer glass envelope. Others will argue that the amount of UV that gets through is not significant and that the corals will adapt just fine. I wouldn't use the word "bad" unless you are talking about excessive UV-B or any UV-C. You will have to decide for yourself if the amount of UV-B is actually excessive.

We are also told that "green" glass (standard glass) allows 73% pass thru of UV-A and less than 1% of UV-B.

Actually it allows 3% of UV-B. That 1% figure was for a special plastic. I don't see any problem whatsoever with allowing 73% of UV-A to pass through and 3% of UV-B is certainly of no concern either.

Now, does the standard tempared glass provide enough reduction? We dont know for sure with out further breakdown of the UV rays.

Standard tempered glass is regular glass that has been tempered. The tempered part just makes it stronger and more heat resistant. It should have the same transmittance properties as regular glass AFAIK. Based on Dana Riddle's measurement of regular glass, I would think that it would be fine.

Now, does this prove or disprove the thread on UV's and the guys 26g tank?

I didn't read that thread past his original post when he posted it and before anyone responded. I didn't want to respond to him at the time because there are too many issues involved here and I didn't feel like having to argue with the UV-doesn't-hurt-anything crowd. First, he put a brand new 250w metal halide lamp over a 26-gal tank with no attempt at any sort of acclimation--he positioned it only 9.5" above the water. He should have started out much higher. Second, he used a double-ended HQI lamp without a shield--something I believe should never be done because of the excessive levels of UV-B and a certain small amount of UV-C that these lamps put out. Third, the effects that he noticed in his tank were caused by more than one thing. The water heated up because of the infra red (not excessive UV-C) from a 250w metal halide lamp only 9.5" over such a small volume of water. The only point here is that any 250w metal halide lamp is likely to cause a 26-gal tank to operate at 3 degrees higher temperature than it previously ran without the 250w metal halide lamp. I'm surprised the increase in temperature wasn't greater. Then there is the fact that the detrimental effects on the tanks inhabitants were caused by both the exposure to excessive UV from the unshielded double-ended lamp and sudden exposure to high levels of infra red that they were not acclimated to. What he should have done was to use a glass shield with his new double-ended metal halide lamp and to start out with the lamp positioned 15" above the water (because it's such a small tank) and also he should have started out with only 4 hours/day photoperiod.

Depends which side of the coin you look at.

In his case, both sides of the coin were bad.

Yes, we all agree he needed the "shield", but IMO everybody needs the "shield" regardless of the bulb used.

I prefer to draw a distinction and say that one should always use some sort of shield with unprotected double-ended lamps (don't forget about that guy who claims he actually has some new Ushio UV-P DE lamps that have UV-absorbing quartz outer glass, so maybe he's OK without a shield) and that it is probably a good idea to use a shield with regular mogul base metal halide lamps.

Did the UV's cause his fish to die?

There were several factors that contributed to stress: Sudden change in their environment as far as intensity of light and water temperature--although I don't believe that alone would have done it, excessive UV radiation, sudden dramatic increase in infra red radiation compared to what they were used to. We know what he did wrong so we can assume that if he had done it properly the fish would have lived. Therefore we know that the various things that he did wrong caused the death of his fish.

The glass under your store bought fixtures are nothing special. They are not the magic bean or kroptonite shield they are made out to be, the are a pc of tempared float glass in my opinion.

Yes, it is tempered float glass. And according to Dana Riddle that works just fine. It absorbs 27% of UV-A and 97% of UV-B. What more could you want? No one ever said it was "special." The manufacturer certainly has never said that. It provides protection from splashing and, according to Dana Riddle's tests, provides more than ample UV absorption. (BTW, Delbeek & Sprung in TRA-1 recommend "tempered glass" shields for HQI DE lamps.)

Ninong

[PerryinCA]

After reviewing some info, it was Richard who posted that info. After re-learning some things, I agree with you guys on the HQI subject. Not entirely sold on the need for a shield with a mogul MH lamp, but I see it as a reasonable possibility.

Here are some quotes. Dana expressed permission to post his thoughts/findings on the boards.

Some hobbyists for various reasons insist on burning halide or mercury vapor lamps without shielding. I guess that I've beat this subject to death, but would like to state that some zooxanthellae do not possess any means of producing mycosporinelike amino acids. But never mind that - it seems that hobbyists in certain, and possibly isolated cases, should take some form of protection from lamp-produced UV.

mycosporinelike aminos are those which help coral survive in UV intensive environments.

Here is some more on the UV issue. The >> << questions posted by Tapio Haaparanta, the response by Dana Riddle.

>>If indeed some lamps put out several-times more UV-A than noon time tropical sun, that is a concern. You mentioned that "some" lamps do that. Isn't that the double-ended Osrams, though?<< No, although UV is quite high from the T-lamps (Osrams & ABs are the only ones we've tested), there was a "shielded" lamp that produced more UV. Please forgive me, my notes are packed and I don't recall exactly which lamp it was.


>>So, the bulbs put out less UV-B than the tropical sun. It seems to me that with exeption of the 11,000 bulb there should be no major concern for UV exposure, if we only look at the lamp outputs. At what distance did you measure the UV? Is the UV intensity still that high once the bulb is the usual 7-12" above the water level and how efficiently is the UV penetrating aquarium water compared to NSW?<< All lamps were tested with the lamps 9.5" inches
above the sensor. Using the inverse square law, we could calculate 44,000 æW UV-A and ~1,000 æW UVB when the lamps are 4 inches above the water! We've conducted UV transmission studies in aquaria. The glass walls tend to bounce UV around and focus it, especially near the corners. We've seen cases where UV levels actually rose with depth! Craig Bingman did some UV experiments a few years ago (I'm sure you recall those).

>>Standard reflectors are usually flat behind the bulb. Isn't the hotspot in those reflectors usually somewhere right underneath the bulb? Have you had a chance to see how parabolic reflectors disperse the hotspots, especially UV hotspots?<< Yes, UV "usually" is focused below or below and forward of the lamp. Parabolic reflectors, especially if they minimize lateral light distribution, are in the "very efficient" category.

>>I am interested because I recently built a new light hood on my 300 SPS tank and it has a parabolic reflector. Contrary to your advice, there is nothing between the bulbs and the water<g>. So far I have not overdosed any corals and I like the way the reflector spreads the light. The light hood has 4x400W 20,000K, 4x96W PC 6700K and 4x110W VHO actinics.<< Generally, PCs and VHOs are poor producers of UV (unless they are engineered for UV production).
Can't comment on the 20K lamps, although I would suspect the UV output is relatively low. As for overdosing, the results may not be immediately apparent. If photoinhibition occurs, and zooxanthellae do not translocate vitamins, amino acids, fats and various other things, then the coral must obtain these through feeding or by relying on energy stores or by cannibalization (is that a word?)_ Depending upon the animal's metabolism, this could happen rather quickly or could take months.

>>I am also wondering how the UV output might change when the lights age (especially the infamous 20K's). FWIW, I run them on HQI ballasts and I get about one years worth out of them, which I think is thanks to the ballast. Hey, maybe you should make a stopover in San Diego on your way to HI and take some measurements <g>.<< Again, I can't make much comment on the 20K lamps, although I suspect the UV output drops rapidly. PC and VHO outputs, in my
experience, degrade rather quickly over a 6 month period. Thanks for the invitation, I'll put you on the list_ since we're moving to Hawaii, there have been a surprising number of invitations_ funny how that works <G>.

>>But I wonder how much would be emitted if the outer envelope would not be there.<< We checked German, American and Japanese metal halide glass _ it ransmits UV surprisingly well (~70% - again my notes are not in front of me). quarium Frontiers has had for months an UV article discussing 2 years' esearch and I haven't even had the courtesy of an "accept" or "reject". on't know who's mad at me there. I'm hesitant to discuss too much of the nfo in that article, since here is an "exclusive" agreement (if accepted, so guess I'm safe). Is my frustration showing <G>.


>>I agree that UV should be an issue if the common bulbs truly emit dangerous levels. Even if the levels are far less, than natural sunlight, the hotspot and reflector issue should be looked into. I have only had a few SPS corals that seemed to have trouble adjusting to my lights. They were not even in the brightest places and I think something else was wrong with them. Then again I insist on using the allegedly highly inefficient German Blue bulbs, so maybe that's why I have never had a light bleaching episode. The coral colors are cool though<G>. << UV and PAR distributions aren't always the same. Consider that UV can be focused by the glass walls_ I wish there were easy answers to this complicated subject.

OK...I just spent the better part of two hours reading on the forums in compuserve, and am trying to take in all the info. There is sooooo much there, much than I could/would want to copy and paste, especially as I feel as more can be learned if the threads are read in entirety . I honestly see it as a great overall resource for technical, scientific and anectdotal information in regards to lighting (both natural and electrical). Dana, Richard and too many others to name have done some interesting things and much of it can be found there. Utilizing the search function there will bring about many hours worth of reading on everything from ballast/lamp par readings to coral coloration. You will recognize many of the names there as well.

-Perry

re-archiving the thread to update with the added information present

[bowfront]

Personally I don’t understand why anyone would want to increase the level of UV in their aquarium. Dana Riddle in Ultraviolet Radiation and Aquarium Lighting, states that “UV (or UV in synergy with high PAR, temperature, etc.) is known to inhibit photosynthesis.” He offers various references to substantiate this claim and then goes on to say “It should be sufficient to say that ultraviolet radiation is potentially harmful to natural and captive ecosystems.” Aren’t we all striving for maximum photosynthesis through high PAR light sources? Actually it may be beneficial to shield all MH bulbs since Dana’s research shows that the glass envelope on at least some mogul bulbs block less than 40% of UV-B emission. Regardless of what you want to call it based on Dana’s research a simple piece of 3/16” glass seems to do a pretty good job of blocking UV-A and UV-B while still transmitting 91% of PAR. AutoHaus UF-3 looks like it would work even better since it blocks more than 99% of UV-B with a PAR reduction of 10%. Unfortunately, there still seems to be little available data on the UV emission level from HQI de bulbs. If anyone has a link to such research could you please post it.

[Ninong]

Originally posted by bowfront:

Unfortunately, there still seems to be little available data on the UV emission level from HQI de bulbs. If anyone has a link to such research could you please post it.

There is the December 1999 Aquarium Frontiers article by Dr. Sanjay Joshi http://www.animalnetwork.com/fish2/a.../2/default.asp that tested 250w metal halide lamps. The 10,000K double-ended HQI lamp in that test was a Ushio and it was tested without any kind of shield.

His measuring instrument was calibrated to register between 310-800nm. Light visible to the human eye is from 380-780nm. Below 380nm is Ultraviolet and above 780nm is Infra Red. PAR is considered to be 400-700nm. UV-A is 320-400nm, UV-B is 280-320nm and UV-C is 200-280nm.

In the following chart, the aqua colored line that peaks so high in the violet band is the Ushio 10,000K HQI DE lamp. You will see a small amount of UV-B between 310-320nm and a considerable amount of UV-A from 320-400nm. We don't know from this test what the measurement is below 310nm because the calibration stopped at 310nm.





Selected quotes from TRA-1 by Delbeek & Sprung, p. 196:

"HQI lighting produces UV light which can be harmful to those corals that lack appropriate UV shielding pigments (Mohan, 1990)."

"Because of the heat generated by HQI metal halide bulbs, only tempered glass should be used for the lens."

"Do not be concerned if small amounts of UV-A spectra are still transmitted by a particular bulb, since the majority of zooxanthellae containing invertebrates require it to maintain their UV blocking pigments and fluorescent colours."

And from p. 186, "Neither ultraviolet nor infrared are visible to the human eye, but they have important physiological affects on coral reefs, as we describe in this chapter and in chapter 3."