Here is the shot you are talking about I presume.
They simply removed the light source in this shot.
Holy crap you just don't wanna believe anyone besides yourself do you lol, that's one of the things DF highlighted, that in the PC version characters are unnaturally illuminated..
in the original edition, there was definitely a sense that Geralt and company were somewhat unnaturally illuminated in order to make them pop out of darker surroundings; the difference now is that they appear to sit much more comfortably within the environments, with the addition - where necessary - of appropriately placed light sources.
DF are saying they ADDED light sources where necessary, to balance out the characters and make them fit better within the environments, so they don't stick out as brightly lit moving things lol.
here let me make it a bit easier for you .. look at this shot, it highlights both versions better points :
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Here you can clearly see the PC version has higher resolution textures, and better anti aliasing, but the lighting sticks out like a sore thumb, the dragon and all three characters in the foreground are so brightly lit ..
where as the 360 version has more refined lighting, the sunlight is brightening the dragon in the right places, and his back side that's in the shade is not unnaturally illuminated, same for the character models, they're "blending in" so much better into the environment. Doesn't take a fanboy or a tech expert to notice this difference.