Don't know if this was in Unreal, but you can choose whether a light affects the world, actors, or both.
There are now 3 Special Light categories for a total of four. These correspond with the SpecialLit1/2/3 check boxes that are now in the Surface Properties menu.
bNegativeLight: This one is fantastic. It makes the light 'negative'. It's great for creating shadows and such, and it's also great when used subtle to break up the hue and brightness of a large texture surface. Note that it is 'negative' in all sense, and the Hue will be backwards from what you're used to. So if your room is lit with a hue hovering around 140, and you put a negative light on there, you'll need to tweak the negative lights hue a bit to find what value makes it cast darkness of the same bluish hue as the room. An interesting side-effect of negative lights that I didn't have time to exploit is that they will override an area's Ambient light and can therefore create a 'dark' area darker than anywhere else in the zone.
There are some caveats: you probably want to avoid doing anything too major or critical with negative lights, as they will look different on different video/machine configurations. Also, if the player jacks up their screen brightness, areas that you've "super-blasted" with negative lights will stick out and look weird - those parts will appear strangely "too dark". But as long as you stick to the subtler side with them, the possibilities are quite great, particularly combined with the various strobe and cloud cast-type effects and such built into Unreal.
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