UVB light length?

[TrebleClef]

I was wondering what the appropriate length would be for a UVB light for my tank. I have a 40 gallon breeder right now, and the current lights that I have are housed in a Zoo Med double domed light fixture. One side has the basking bulb in it and the other side has the UVB. I now know that the "coiled" UVB isn't good, so I went off of the suggestions of others on this site and recently bought a Reptisun 10.0 tube UVB...however my question is what length should I have bought for my tank size? The light I bought is 24" in length. I thought I had chosen the 18" version of the light when I purchased it on Amazon, but somehow I must have mistakenly chosen the 24" version. I'm wondering if it isn't too long for my tank (which is 38 x 18 x 18). I mean I know it will obviously fit in the tank - I just wasn't sure if the UVB light should cover that much area or if you want to have part of the tank that doesn't get any UVB. Not sure that I'm asking this in a way that makes any sense.

 

[erikadickson]

That should be the perfect length! I believe it should cover at least 2/3 of the tank.

 

[TrebleClef]

Thank you ericadickson! I appreciate your reply

I don't know if it makes a difference, but the exact bulb I bought is the one in the link below. A Zoo Med Reptisun 10.0 High Output UVB Fluorescent Bulb 17 watt, 24". I wasn't sure whether it being "high output" was overkill or not. I've seen other bulbs on Amazon which are identical to this, Zoo Med Reptisun 10.0 etc, only they are not listed as being "high output".

http://www.amazon.com/gp/product/B0009YHSWK?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

 

[erikadickson]

Sounds like you've got yourself a very good bulb! Reptisun t5 10.0 HO are very highly recommended bulbs

 

[Taterbug]

The Amazon listings are really confusing, pay attention to the wattage on the product photo to know what your buying.
The 24" 20W bulb you have linked is a T8, it's still a good bulb but just so you are aware and have the correct fixture for it. The two types have very different setup requirements as far as distance goes. This illustrates the relative strength of a few different bulbs in different types of fixtures. https://sites.google.com/site/thelizardmadness/lighting-guides

For reference.
The T5 is a 22" 24W bulb. http://www.amazon.com/Zoo-Med-ReptiSun-Output-34w22in/dp/B00AQU8HAO/ref=sr_1_3?s=pet-supplies&ie=UTF8&qid=1441325613&sr=1-3&keywords=Reptisun+T5 The easiest way to tell is the packaging, the T5 bulbs show the bulb in a little window and the T8 are packed in a box.