UVB reading on a T8 5.0 bulb without screen or lid

[new-tegu-care]

I am currently building a new enclosure and installed a T8 5.0 UVB bulb inside without any blockage. I was wondering if anyone knew the Fergerson scale without the lid or screen in place on this linear t8 5.0. I don't have enough funds to buy a reader but I also don't want to put my tegu at risk for improper care of lighting. so if anyone out there knows anyone at a reptile store with a reader or has one personally, it would greatly be appreciated to get the correct distance reading of 2.6 UVB.