Measuring bulbs...

[thomasina]

I have a 20g high tank. I want to replace the fluorescent blub. I measured the old one glass end to glass end and thought it was an 18 inch. Ordered it, and its an inch to short. How do you, and what do measure to get the right bulb? end of the glass or to the end of the two little metal thingies?
(mechanically challenge here)

 

[Laser]

The 20 high tank should use an 18 inch tube. Did you order the correct diameter? You probably have a t8 fixture instead of a t5. Perhaps they sent you a wrong bulb?

 

[thomasina]

The 20 high tank should use an 18 inch tube. Did you order the correct diameter? You probably have a t8 fixture instead of a t5. Perhaps they sent you a wrong bulb?

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It says on the package that it is 18 inch but its an inch short. I got it at Amazon and in the process of returning it. Diameter? That is around, does that make a difference in length?
It is also a T5, which is what I want and this is the only one I could find in 18 inch. I just don't understand how they measure it though.

 

[thomasina]

Check this out??

 

[armymp327]

what type of light fixture do you have? you have to order the right bulbs for the corresponding fixture, for example only T-5 bulbs will fit in a T5 fixture (or ballast) that 18 inch bulb is either T-8 or even T-12 (probably T-8)

the smaller bulb is a T-5 bulb because it has a smaller diameter but more power. but also requires a high powered ballast that only a T-5 fixture will have