Without it when there's concealment (even just some wimpy fog, or dim light) you can't usually sneak attack, as you can't quite make out the cracks and gabs in the armor, the or exactly where "between the ribs" is on a naked dude. Low-light vision, under the right circumstances, would allow him to sneak attack, as would blind sight but the latter is a monster feature, thus for biological and mechanical reasons is impossible (or hard?) to get.
I understand blind-fight is having a good sense of where that enemy is. If I know where the torso is, I know where his heart is. Anecdotal/personal evidence: A martial artist friend of mine can, while blind folded, hit really hard towards an object and stop right in front of it, which is probably just being extremely mindful about where you are.
Question: Now how does blind-fight work? In dim light, would blind-fight allow the rogue to keep sneak attacking?
Best Answer
No, Blind-Fight does not allow you to sneak attack a target in dim light.
Sneak attack says (emphasis mine):
In order to perform a sneak attack on a target with concealment, then, you must have an ability that negates the concealment. Blind-Fight does not do this:
Blind-Fight doesn't negate or remove concealment, it only gives you another chance to connect when you miss because of concealment. Fictionally, Blind-Fight doesn't represent being able to see better; rather, it represents having tuned your other senses, your focus of attention, and your knowledge of fighting toward being able to predict where your opponent is going to be even when you can't see them. Since sneak attack doesn't simply need you to know where your opponent is, but has the tougher requirement that you can see them well and that they not have any concealment, Blind-Sight is doesn't help meet the requirements.
Low-light vision can be of some help. Low-light vision allows you to see twice as far as a normal human in each type of light condition, so you can be twice as far from the light source before your target gets the concealment of dim lighting. But once low-light vision's benefit is factored in and it's found that the target does have dim light concealment from the rogue, low-light vision does nothing more for our hypothetical rogue – it doesn't make dim light any less concealing.
Blindsight is a monster ability that represents echolocation or being able to sense via vibrations. Blindsight would negate concealment due to lighting conditions, allowing a rogue to sneak attack, but how a rogue is going to acquire blindsight is a bit of a trick.