This is actually the HDR function from trueBloom. It uses a simple cubic curve centered on the HDR value to give the appearance of dynamic lighting ranges of light. The actual range visible is different inside and outside, and can be tweaked by the user.
This shader adjusts the range you can see. It's a bit hard to see from screenshots, but you can see where the sky is bright when you're looking at the land. The adjustment is visible ingame.
Screens:
http://s4.photobucket.com/albums/y145/peachykeen000/enhdr/
http://i4.photobucket.com/albums/y145/peachykeen000/enhdr/enHDR0.jpg
http://i4.photobucket.com/albums/y145/peachykeen000/enhdr/enHDR1.jpg
http://i4.photobucket.com/albums/y145/peachykeen000/enhdr/enHDR2.jpg
http://i4.photobucket.com/albums/y145/peachykeen000/enhdr/enHDR3.jpg
http://i4.photobucket.com/albums/y145/peachykeen000/enhdr/enHDR4.jpg
http://i4.photobucket.com/albums/y145/peachykeen000/enhdr/enHDR5.jpg
http://i4.photobucket.com/albums/y145/peachykeen000/enhdr/enHDR6.jpg
Temporary Download:
http://www.mediafire.com/?doymon1yzhj
To use all the features of this shader, you need the enhanced MGE dll found here:
http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7548
Select whichever version corresponds to your build of MGE.
If you choose not to use the enhanced dll, the shader will fall back to always using the outside HDR setting.
Also, the trueBloom shader includes HDR already, as do many of the shaders that come with MGE. Don't use multiple hdr shaders, it'll make things look really weird.
This can be used with ENB's bloom if you use that, but again, disable the ENB hdr or things will become too extreme.