This hdr.fx file disables the brightness auto-adjustment effect that occurred when using the HDR lighting feature in the D3D10 renderer (ClassicLighting = False).
The brightness would dynamically darken in the presence of bright lights, but would take up to 30 seconds to readjust, apparently for attempted realism.
This created real problems during gameplay whenever bright flashes or many light sources were viewed at once, e.g. from explosions.
The preview image shows the lasting effect of looking at several flares before and after the fix. The game would become unreasonably dark before, but renders without issue after the fix.

To install, drop the hdr.fx file into "Deus Ex\System\d3d10drv\", backing up the original as desired.
Be sure to have ClassicLighting set to false in gmdx.ini and the Direct3D 10 renderer selected in the Kentie's launcher configuration options to enable HDR lighting in the first place.

All credit goes to Veronika, who gave me permission to upload this addon. All I did was add a preview image and this readme file.

-RoSoDude