The environment light effects are controlled by the sirensettings in the carcols, in particular the lightFalloff and cone settings. Some people prefer more extreme values to get reflections on the car body or even in the lightbar, however this has the downside that the reflections will be visible inside and underneath the car as well. Others like me prefer more simple settings with weaker reflections that don't make the shortcomings of the game so obvious, I use the following settings for example:
XML
<lightFalloffMax value="150" />
<lightFalloffExponent value="150" />
<lightInnerConeAngle value="15" />
<lightOuterConeAngle value="50" />
You'll probably need to play around with your settings to find the ones you like the most, the easiest way to do that is in-game with LiveLights.