Difference between surface and substrate in temp with uth

[kitedemon]

You can't, temp guns only read surface temperatures.

To the OP:

The UTH you have on the cool side is 100% pointless. UTH's do not increase the temperature of the air inside the cage. You need to use a heat lamp or CHE to increase air temperatures.

Your temps are all fine, but you need to get something to measure air temps.

I would add any lamp will increase air temps I use fluorescent lights and led strings to do so.

UTh and other radiant heat sources only heat things not air they can raise a small amount but it is very limited.