Just like the title says. I have paintings on the wall that are completely in shadow, even though I've placed lights next to them (I'm not convinced Lights actually generate light). Even if lights generate light, there are no ceiling hooks in the basement so there's no way to brighten up the area.

Please raise the ambient light by a whole bunch, thanks.

My recommendations would be

1) Zakuulan Standing Floor Lamps--These come from Star Fortresses and fit on small, medium narrow, and medium hooks so are pretty versatile. They do give off light at a nice level of brightness, and the affected area is a good size.

2) Luminous Sconce: Yellow--These give off a fairly bright light, though I think the size of the affected area isn't huge. But they go on small wall hooks, which means that they can go between the windows in the two underwater side rooms, and even, if you like, on the ceiling hook in those rooms, which is actually a small wall hook. They are apparently in the Corporate Retreat Decoration Bundle, but they were also in an older pack, and you may find them sporadically on the GTN.

TOR Decorating has a list of lights that actually give off light (may not be complete): https://tord.mmo-fashion.com/category/database/database-themes/miscellaneous/casts-light-yes/

but I think for your situation--trying to brighten the dark Manaan underwater rooms--the above might be good options.

I actually kinda like the dim default lighting, I've had fun using luminescent decorations down there such as the plant decos from the Rakghoul event. However, I really wish there were some larger ceiling hooks in the side rooms. Mireleni above has some great suggestions -- I use those same floor lamps myself, actually -- but I was trying to make a lab room and the lack of ceiling hooks to decently light it was such a design killer.

It would be awesome if SWTOR borrowed a feature from FFXIV housing: the ability to set the overall lighting level for your house (you can choose a level from 1-5, dark to really bright). It isn't perfect, but really helps customize and set the tone of your place.