Since I didn’t leave Taiwan for CNY I had to haul my classroom fish home… A siamese fighting fish from a summer program 2 years ago that just won’t expire. Carl (the fish) is in his little plastic aquarium box on my desk in my den. My house doesn’t get too much light after 4pm especially at the back where my den is. I’m a bit worried about Carl because he spends a lot of the time in the dark. I don’t want to leave the lights on when I’m not home and it doesn’t matter where I put his aquarium box because my house is pretty dim for most of the day. So when I come home, Carl is just floating (not upside down) in the corner of the tank. Is he sleeping? He’s not moving. Is it because he’s not getting enough light? Is this bad for him/her? Do fish need a certain amount of hours of light to live?
Ner, he’ll be fine. My Thai fighting fish, Sashimi (God rest his soul) floated about a lot as well.
One thing could be lack of oxygen. Change some of his water and that will perk him up.
Plants or algae in the water presumably need light to produce oxygen. Not sure how much though.
A very small amount. They need only about 10% of the direct sunlight “average” plants require (no such thing as average plant but you can guess my meaning as a rough guide). However because they usually create a thick layer on top of the water, the algae underneath can recieve virtually no sunlight. You should thin out the algae on the top, to stop it blocking any light to other algae. So every week or so thin out any alage floating on the top. Algae also need other stuff like CO2 but as it sounds like you have a load of dead algae then that isn’t an issue. 
Speaking of Thai fighting fish (betta) I have now got some Formosan fighting fish. They look completely different, but are quite interesting and not as aggressive.
To answer your question: no, fish don’t need much light to survive.
But if you want to see your fish behave more naturally, you could improve its surroundings, by adding a little circulation, more light, a slightly larger tank, and/or more plants.
The fact that you frequently see yours sitting still in the corner implies that it’s in a less-than-perfect environment.
funnily enough, they enjoy company. mine freaks out when i leave her over the weekend.
thye don’t really need much light as they are quite at home in muddy rice paddies and ponds. but they do get bored.