Return the bulb - use the 5.0 for now distance 6-8 inches no obstruction - I always have spare uvb's for just that and replacement plus when the pandemic hit I couldn't get the Arcadia's I was using so I went to the reptisun bulbs- they interchange for your fixtureGood to hear about humidity thank you. New issue is I don’t think my 10.0 UVB is working properly. The 5.0 is brighter.
Low exposure in both these photos so you can see the issue.
View attachment 72366
^ 5.0 UVB working well.
View attachment 72365
^ 10.0 UVB seems “dead” in the center. The center also has kind of a wavy flicker..