In D2 LoD, light radius meaningfully increased your vision in very dark areas like the Den of Evil and Underground Passage. Even just +1 light radius made a noticeable difference.
In D2R, it basically has no effect because it is a very, very tiny increase in brightness on the edge of your default light radius. You can easily see this by switching between legacy and D2R graphics and taking an item with light radius on and off.
This would be a nice bug to fix, because D2R is indeed very dark in some areas (not a complaint, well done to VV for preserving the darkness/feel of the original) and light radius would be very beneficial in these areas if it worked properly.