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In Diablo I, Light Radius was actually fairly useless, as whilst it allowed the player to see longer distances, it also meant monsters could see the player more easily as well. As such, it was to your advantage to have a lower light radius.
In Diablo II, Light Radius wasn't much more useful as most of the game occured in well lit above ground areas, and no one really cared about it much. Generally it was just a worthless weapon modifier.