question about measuring bulbs

I need to replace the bulb in one of my fixtures. I am sure if I should measure from prong to prong? Or just the actual bulb part? When I measure from prong to prong its 18" and the bulb alone is 17". Its a t8 bulb. Just want to make sure I buy the right thing, as I am more than likely buying online. Thanks in advance.

 

By standards, it should be known as a T8 18" (450mm) Tube. Does your current tube have any markings to identify it?

If it is a standard 18" tube, it will most likely be 15W.

Flourescent tubes are generally always a common size, with common power ratings.

 

yes its 15w, which is why I want to replace it so I can grow plants. But having a heck of a time finding anything in more w's than that for the size that isn't t5

 

I doubt you'll find 18" T8s greater than 15W - it's an industry (lighting) standard.

The other thing to consider is the ballast in the fixture. The ballast supplies the power to the tube, and wil be set to a certain wattage based on the length of the fixture.

 

yeah I ended up just buying a t5 fixture. its not super high light but atleast its ~1.8w per gallon

 

Watts per gallon is kind of an old rule when it comes to lighting now.

Did you get T5 NO (Normal Output) or T5 HO (High Output) - refer to this thread for the lighting chart



This will give you an idea of whether or not you have high/medium/low lighting