Whether or not betta fish need light, is actually a pretty simple question to answer, yet also a fairly complex one. This is really a two sided question, because betta fish do need light, but they also do not need it. First and foremost, betta fish are tropical fish, and tropical places are warm and have lots of sun light, so yes, betta fish do want light, they like it, and they definitely need it during the day time.
So, Do Betta Fish Need Light?
To explain this a little better, they are actually kind of like humans in the sense that they like to have regular sleeping patterns. This means that they like to have light during the day when they are awake, and they like to have darkness for the night time when they want to sleep. This post covers where Betta fish live originally & naturally.
That being said, your best option, and the best thing for your betta fish, is to turn on your aquarium light in the morning and then turn it off at night before you go to bed. This is so that your betta fish can have a stress free environment with a lot of light and regularity.
Moreover, you do want your aquarium to be as close to the real thing as possible and you want it to resemble the betta fish’s environment without question and that means having light. Remember that direct sunlight is not the most ideal thing for your betta fish because too much sunlight can cause excessive algae growth, which can in turn suck all of the oxygen right out of the water.
If you do have a UV light, you will also probably need a UV sterilizer to prevent algae growth (more on removing algae here). The best way to go is with a generic aquarium light, or even one with day and night time settings. It's also important to get the right kind of Betta fish tank.