Unless you have access to a Solarmeter 6.2 or 6.5 , and can test the output of your source can reset the basking spot to UV source distance to get a higher level of UV ( applying the inverse square law ) or by trial and error , T8 and compacts have a useful life of 6 months , most T5ho tubes have a useful life of 12 months (Arcadia Reptile GUARANTEE at least 1 year ,
https://www.arcadiareptile.com/d3-dragon-lamp/).
Inverse Square Law (very briefly)
The math of the physics
and
and
If you know someone who has a Solarmeter 6.2 (UVB microW flux meter) and you can measure the UVB flux at the basking spot and it's over 60 microW / sq.cm , you still have some useful life in the tube if you can move the basking higher to get the new level of flux to about 180 microW / sq.cm then you can extend the life of the T5 tube several months.
This is my approach with my UVB globes and will work with T8 and T5ho tubes.
Alternatively if you know someone who has a Solarmeter 6.5 ( UV-Index meter ) , measure the currently UV-index and if it's under 3 , see above , adjust the basking spot height until the new UV-Index = 6.