This is deeply impressive and a run I had never even considered trying before. I play with cheats on, so I wonder how far one can get with cheatsrelated on but without using lights. I'll have to give it a go and report back sometime.
It's actually less impressive than it seems. I don't play with cheats enabled but I do use the botnet mod that shows how each choice effects stats. Using that and some trial and error revealed a few things that aren't readily obvious to the player. Let's do a breakdown on a few of the girls for example.
Monica, Mrs. Wilson, Sophia, Kayla, and Ward are all pretty much down to bone out of the box.
Nadir, Rio, and Heather seem like they need work but it's a lot less than you'd think. For example you can ignore Heather entirely until late in the game at which point you basically just step in when she's fighting with Kyle. Nadir you just listen to her marital problems, go to dinner at her home, and deal with the husband (either way) and you're good.
That leaves what I would call the "deceptively difficult" options: Mrs. Maywood, Brittany, Mrs. Hill, and Karen. I used to think that these women in particular would require a lot of stat/light manipulation but they don't. You basically just need to be past a certain stat threshold and you're done. Karen for example. Just ignore her completely until you meet the stat requirements and then go get a snack with her once you have the option to. And boom you get the option to confess your love to her or whatever. Basically the same with Mrs. Maywood and Brittany. If you know the stat trigger and the appropriate time it's a done deal.
Obviously that's not the full list of love interests but it's most of the main ones. At this point I'm just seeing how many others I can wedge into a low-light or no-light run.
I think Nikki and Sydney are available without lights too. Not sure about Suzue, that might require an orange light but not sure. Ive never ignored the orange light to see what happens.
Yeah didn't check Nikki beyond getting her number so far. And Sydney seems easy too. My current save is a no-light run and I made it through the bunker with Suzie. Doing that nets you decent progress so it may be do-able.