How do I find out what size bulb I need?

[Fo0]

Hello,

Do they make different size diameter T-8 Bulbs? I bought a new bulb thinking I needed a T-8 but wasn't sure and it seems to be about 7/8 inch. My old light I am looking to replace is bigger (about 1 1/8 inch). It is about 14 years old. I attached some pictures. The top and bigger one is the size I need. Thank You.

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[BettieL]

The larger light looks more like a t-12 light especially if its 14 years old I would bet on it being a t-12.

[Fo0]

i've read that t-12 is 1.5 inch diameter. It also said that t-8 is supposed to be 1" in diameter which is closer to what I need. But I dont know why my t-8 is smaller than 1 inch? do they make different size t-8? Thanks

[prostreet69camaro]

Looks like a T-8. I have an aquarium w/ light that is 20 years old with a T-8 light.

[jijome]

How to assure that the bulb is T-8