What was this effect? Darkening certain walls

[Marscaleb]

I recall reading about an often overlooked effect Doom did in its rendering.  If a wall was facing directly north or south, it would make it slightly darker, and if it were facing directly east/west, it would make it slightly brighter.  (Or maybe I have it backwards?)

 

I think I read about it on the Doom wiki, but I don't recall what the effect was called, so I don't know how to find it.

 

Can anyone elucidate me here?  I'm trying to look up some specifics about how this worked.

[Plerb]

https://doomwiki.org/wiki/Fake_contrast

[Edward850]

https://doomwiki.org/wiki/Fake_contrast

And it's quite well known, in the sense that it's particular behavior has been known to be debated amongst mappers at times.

 

Edit: darn you @Plerb!

Edited March 13, 2024 by Edward850

[Plerb]

Haha :p

[Marscaleb]

Thank you Plerb, this is just what I was looking for!

 

And clearly no thanks should be given to Edward850, since he wasn't first to reply.  Instead you get this!.