From Mods Repository Wiki
There are few commands to enable this mode and to modify its options.
To use this feature you have to modify your BAT file for compiling map, here is example:
flare -extra -sundiffusesamples 10 -visual -width 1024 -height 768 -fullscreen -dumpoptions ../../main/maps/mp/bx_dawn
You can also debug view in flare, to modify your flare settings go to:
"c:\program files\call of duty\tools\bin", and modify flare.cfg
You can add your own binds there. For more informations about avaiable commands read CFG file.
In this step im just showing how it looks when its enabled.