Advice??

Hi! I have a 48 inch length tank for my beardie. Should I buy a tube light that’s 48 inches long?

And if I did buy a 48 inch tube light, would it work?

This is what is recommended on the forum for UVB -- it is up to you how long you want the light a 36" would work as well --- here is the info --
Which UVB light should I use?
The best UVB light is a ReptiSun 10.0 fluorescent tube HO (Or Arcardia 12% in the UK). Compact or coil bulbs do not emit the proper amount of UVB light for a bearded dragon, and should not be used. Other brands, such as the Zilla Desert Series and ReptiGlo have been known to cause eye problems and other health issues with bearded dragons, and should be avoided. The reason that some UVB lights (Zilla, ReptiGlo, coils/compacts, ect.) are considered dangerous is because the wavelength of UVB that they emit is shorter and more intense than the wavelength of the "safe" lights (ReptiSun, Arcadia).
UVB lights should be replaced every 6 months. The T5’s are a strong bulb and only need to be replaced once a year – the T 8 every 6 months--- where as the T 8 are not as strong—they need to be placed inside the tank the T 5 10.0 bulb approx 10-11 inches from basking spot – the T 8 approx 6-8 inches from basking spot—the cover needs to be off the bulb for full effect of the UVB rays-- just make sure its a 10.0 not a 5.0 HO
Karrie

You want there to be some areas with low or no uvb so your dragon can escape them if it wants to the 36 would do fine. The 22 would work too. If you're using the t5 HO bulb.

-Brandon