As many of you know, I have long asserted that trollish darksense perceives darkness as an element. That is, it is not sonar. So, darksense could take a circuitous route from one patch of darkness, around a patch of light, to another patch of darkness. It's true IMG.
In any case, it appears that some folks in the real work have similar views of darkness:
https://www.msu.edu/user/dynicrai/physics/dark.htm
This started all kinds of Glorantha ideas for me, so I thought I would pass it along. One Gloranthan fact that I would add to it is that darkness is always hungry, which is why dark-suckers (like candles) are consumed as they burn.
Chris