Maybe some way to see if a unit is considered illuminated or in darkness, though? In Piratez this can be very hard to tell because there are some really weak light sources (looking at you, Boomfruit), yet for spotting purposes the engine only distinguishes between "fully illuminated" and "in complete darkness".
I would vote for having an illumination indicator. The most useful way would be like the nightvision color change at the press of a button, but only for illuminated tiles that you can see. This is kind of counter intuitive as you should see illuminated tiles anyway, but that is not always the case depending on terrain. The problem here is not the light source but the palette of some terrains. See the attached picture. The selected girl, Lyrical Ox, is fully illuminated. The tile next to her is not. There is no graphic difference between the tiles, because the palette does not have enough colors to display it. The only way to know whether there is light on that tile or not is to look at the light source, guess what it's light radius is and then count tiles.
Counting tiles is not fun, but you have to do it from time to time. I do it in night missions, when I want to know if I'm far enough from the enemies or not. I would welcome an indicator for sight distance of enemies (if enemy is researched), because it would save me from counting tiles.
I have other distances that I sometimes would like to know (snapshot range for example). Maybe some kind of universal distance tool can be programmed to eliminate any form of tilecounting? Press button, then a popup window presents you some choices:
1. Show distance circle of [enter value] tiles around selected friendly unit
2. Show distance circle of [enter value] tiles around spotted enemy units
3. Show light radius of light sources
Another hotkey to display the last choice, so you don't always have to go through the choice menu.