Weird UV Question >Well, perhaps it is not so weird.  Hopefully it will help many. I have a Coralife Turbo-Twist 3X (9W) UV Sterilizer.  It uses a Philips PL-S 9W UV-C bulb (also has TUV on the box). Aquarium suppliers charge between $25 and $35 for replacement bulbs. I did a Google search on Philips pl-s 9W and found a supplier that sells them for $3.50 apiece!!!!! >>Egads! >But then I did more research.  Turns out Philips makes 5 versions, the only difference being the Kelvin rating (27K, 35K, 41K and 50K).  Nowhere on the bulb box, on the bulb, or in the Turbo-Twist documentation is there any mention of Kelvin rating. >>Not uncommon on bulbs not designed for such specific applications. >So the question -- does anyone know which version this unit uses, and does it matter (I presume it matters a lot but my physics is in my distant past!) >>BOY!  I sure don't, and I've never used a U.V. sterilizer, either.  I would contact the manufacturer to get specific information.  By doing that, you will satisfy one of two questions: 1)determining pertinent wavelength & manufacturer information or 2)determining why these bulbs may not be offered for sale or are otherwise unsuitable for this use.   >Thanks! If these bulbs are usable I'll be happy to send the link to the supplier!  Joel >>Please do let us know anything you find out.  More knowledge is definitely BETTER.  Good luck!  Marina Re: Weird UV Question >Well, two things happened between my note and your reply.  First, I contacted a bunch of folks as you suggested.  Second, I remembered my college physics (I started out in astrophysics before becoming an expert in Russian Politics).  The first proved useless for the most part.  Even the manufacturer had no answer.   >>Hrm. >But then my physics reminded me that these bulbs are emitting in the ultraviolet, not visible range.  So they will not have a Kelvin rating.  The bulbs mentioned in the post and that list for just a few dollars are in opaque (mostly) white tubes that filter out much of the UV light.  In a weird twist of capitalism, that SHOULD cost MORE, but they sell for a pittance. >>AHA!  That makes sense...and I'll just admit right here that I've had no such physics education.  I can tell you that the tubes used for U.V. bulbs are made of quartz, though.  IIRC!   >The bulbs in UV sterilizers, however, are in clear tubes and emit at wavelengths that make them germicidal, sterilization devices.  They are primarily used in the medical profession and in other select applications, such as ours.  This is what makes them cost more.  Other than the outer tubing, there is little that distinguishes the $35 from the $3.50.   >>Again, IIRC, U.V. wavelengths will be on the order of something like 400nm-320nm. >Fortunately, I did find a supplier that sells them for $15.  It is: http://www.worldwidespecialtylamp.com/phil3.asp >>Great! >Thanks, Joel >>Thank YOU, Joel.  Lots of folks will be happy to spend so much less on these bulbs.  Marina