Simplified thermodynamic system.
If Each ball=40J
Then without the Green box the Blue box would receive and emit 150J/sec and working back from S.B, emitted E=T^4, has a temp of ~ 196KWith the Green box returning and extra 10J/sec to the Blue box as back radiation it emits 160J/sec and has a temp of 200K.
The Green box receiving and emitting 40J/sec has a temp of ~141K
For the context and further explanation please see the full post.