lighting How do you measure lights?

[PepperZ]

Some of my grow lights died. 
 
https://www.1000bulbs.com/product/89108/SUN-901589.html These are essentially the same specs for the lighting system.
 
There are other brands listed too. I don't know if I should be getting 45.2 inch or 46 inch because I'm not sure how they measure the bulb size. Do they only measure the actual bulb or do they include the half inch prongs as well?  
 
Thanks lol.

 

[alkhall]

54 Watt T5HO lamps are the same length, regardless of manufacturer.
 
I use the Spectralux 901618 myself.

 

[bucdout57]

Good to know. I just ordered a new light set from Amazon for this coming season . Thanks for the question and answer.