My father(tenured professor and research scientist) insists that the 12K's I have on my tank are harmfully sending out ultraviolet light. I don't believe anything without proof. Is there any spectral analysis of these bulbs online that show their output over the lower end of the spectrum? Do the 12K's put out a significant portion of ultra violet? How about the 20K? Thanks.
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12K, 20K MH and Ultraviolet Radiation
- Thread starter dendronepthya
- Start date
UV protected bulbs use a quartz sleeve to absorb the UV and so it's true that these bulbs do have a dual envelope. However, most dual envelope bulbs do not have a quartz sleeve and so offer no UV protection.
The "true" manufaturer of the bulb will be able to answer your question. Send them an email.
Generally the packaging for the bulb will be marked as "UV-P" if the bulb has UV protection. Interestingly though, this is not a guaranteed test. For example, the BLV 10K bulb HIT-DE 250 (double-ended FC2 mount) has packaging that says it is UV-P although the manufacturer has confirmed to me that it does not have UV-P (I was "sun burned" by one of these bulbs and so queried with the manufacturer why this had happened - they went so far as to say that it's well known that all bulbs used in the aquarium industry need UV protection).
The options for getting rid of the UV are:
1. lexan - a polycarbonate (plastic). It's very strong but does scratch easily. It will deform if it gets too hot. All of the clear lexan sheets available block UV.
2. acryllic - much the same comments as for lexan - Hamilton uses this (so they said when I asked).
3. Toughened glass with either a laminate or a chemical coating.
The "true" manufaturer of the bulb will be able to answer your question. Send them an email.
Generally the packaging for the bulb will be marked as "UV-P" if the bulb has UV protection. Interestingly though, this is not a guaranteed test. For example, the BLV 10K bulb HIT-DE 250 (double-ended FC2 mount) has packaging that says it is UV-P although the manufacturer has confirmed to me that it does not have UV-P (I was "sun burned" by one of these bulbs and so queried with the manufacturer why this had happened - they went so far as to say that it's well known that all bulbs used in the aquarium industry need UV protection).
The options for getting rid of the UV are:
1. lexan - a polycarbonate (plastic). It's very strong but does scratch easily. It will deform if it gets too hot. All of the clear lexan sheets available block UV.
2. acryllic - much the same comments as for lexan - Hamilton uses this (so they said when I asked).
3. Toughened glass with either a laminate or a chemical coating.
Your 12K and/or 20K Metal Halide are not significant UV sources if they are the single-ended (Mogul socket) type.
Here's the full scoop:
<UL TYPE=SQUARE><LI> The inner envelope of all MH lamps is quartz. This is so it can withstand the high temperatures and has little to do with UV.
<LI>Quartz is transperant to most UV. This is why quartz sleeves are used in UV sterilizers. Quartz transmits UV between 180nm and 400nm. 400nm is roughly where visible light begins.
<LI> Sunburn and cellular damage is caused by both short wave UV (below 180nm) and by long wave UV (350nm - 400nm).
<LI> Of these, the short wave is by far the most damaging.
<LI> The UV protected quartz Teapot refers to has a cutoff around 220nm to filter the short wave UV. Most MH bulbs don't use this, nor do they need to.
<LI> The outer envelope (the part you can touch) is glass. Most glass is opaque to UV, the exception being glass with a high quartz content (90% +), which is not used in MH lamps.
<LI> On a single ended MH bulb, the glass outer envelope is an effective UV shield.
<LI> There is no UV shield built-in to HQI lamps, since they consist of just the inner quartz envelope. These lamps must be used with a glass shield in the fixture.
</UL>
Here's the full scoop:
<UL TYPE=SQUARE><LI> The inner envelope of all MH lamps is quartz. This is so it can withstand the high temperatures and has little to do with UV.
<LI>Quartz is transperant to most UV. This is why quartz sleeves are used in UV sterilizers. Quartz transmits UV between 180nm and 400nm. 400nm is roughly where visible light begins.
<LI> Sunburn and cellular damage is caused by both short wave UV (below 180nm) and by long wave UV (350nm - 400nm).
<LI> Of these, the short wave is by far the most damaging.
<LI> The UV protected quartz Teapot refers to has a cutoff around 220nm to filter the short wave UV. Most MH bulbs don't use this, nor do they need to.
<LI> The outer envelope (the part you can touch) is glass. Most glass is opaque to UV, the exception being glass with a high quartz content (90% +), which is not used in MH lamps.
<LI> On a single ended MH bulb, the glass outer envelope is an effective UV shield.
<LI> There is no UV shield built-in to HQI lamps, since they consist of just the inner quartz envelope. These lamps must be used with a glass shield in the fixture.
</UL>
You all may want to try a search on this topic. It has been controversial on this board in the past. One of the main issues over which people seem to differ is whether to cover the tank at all. Personally, I did some research and found that (a) unshielded aquarium lights do put at least some of the more harmful-wavelength UV into the tank and (b) plexiglass "G" sheet (the cheap stuff) is a better shield than glass and does just as good a job of shielding as the more expensive polymers. My plexiglass cover hasn't warped with my VHOs 1" above it. I have no experience to offer with MH. A few months ago, someone posted a link to an article in which the UV and UV shielding issues were researched and discussed. There is also a company that will custom-cut sheets of plastics disscussed in the messages above and send them to you. The link for that company should also turn up with a search. Good luck.
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