I’m new to this so I’ll just pop what I was told here by very helpful members and other threads I found searching here
The 14% one has only ( as far as I am aware) been tested in really tall vivs thoroughly but a lot of testing has been done of the 12% so you’ll found a lot of info in old threads here on the 12% about uvb at a given distance and 30-35cm is the ideal tube to basking length to reach the 200microW mentioned above
The best way someone explained it to me is that they need 200 microW at their basking spot. A t8 at 6”-8” is around that and then it dwindles to low or nothing or next to nothing at the floor of a 60 cm tall Viv. A t5 12% Arcadia is high microW at 6” so too high as basking area for a beardie - way more than the t8s microW amount at same distance. It reaches the 200 microW at 12” so you need basking spot there (30cm from tube)
Then the floor of the viv still has a reasonable amount of uvb unlike the t8 floor amount. Hence why you need areas away from it in the cool end
The recommended length of a t5 is half the length of viv and do not exceed 3/4s the length of viv
I’m going for half the length in my 120cm long viv
And def do not have both ( your t8 and a t5) thats waaay to much uvb
I hope I regugitated the right info forward from the lengthy conversations I was lucky to get teaching me how to do the best for Marlow’s lighting