So you get the icon light, half and half, dark, if you are hidden. But how do you know what light conditions you are in when you are not hidden? There are a lot of items that provide bonuses when obscured...does that imply that you are never obscured unless you are hidden in half dark or full dark?
Bonuses when obscured work without hiding. Obscured and hidden are separate things, being obscured makes it easier to hide!
Buffs like Covert Critical on the Dark Justiciar Helmet (which is the important one I'm assuming) actually show as a buff next to your character as soon as they are standing in dim light (lightly obscured, half sun icon). So you'll know if it's active by looking there.