Whether your in a dungeon or it just happens to be nighttime light is an important thing to have. That is it is important if you have anyone that actually needs it. Humans do, that's for sure but if you don't have anyone that needs it to see what good is it?
First there is the fact that most of the see in the dark type ability's don't let you see certain things. Darkvision only shows black and white so its fine if you want to read but one puzzle dealing with colors and your stumped without a light source. Infra-vision is fine if you only want to see living creatures that put off heat in a way that distinguishes it from the background but a number of nasty things don't and if you want to read anything your out of luck. So even if you don't "need" light a group should always have some kind of light source. I know that if I had a group that tried to go without any I would have all kinds of "fun" with them.
Next on the list of reasons you need a light source is that you can use it for things other then light. A torch is a club that also deals fire damage. Oil is fun to throw on monsters and burn them along with the fact that an oil slick will slow any pursuers when you run. Even the old trick with putting a continual light spell on something is quite useful because you can drop it down holes and such to see how deep they are and if anything important is at the bottom. Just make sure you attached it to a rope or something if you want it back. Along with all this there are a number of monsters you will want a fire source when you fight them. After all it would be quite annoying to finally kill the troll and not have any fire available, at that point even just a lit torch would be nice.
Finally it is better safe then sorry. What happens if the party gets polymorphed into humans? What about if you find an important NPC you need to protect who can not see in the dark? All this and more can happen and as I said above if you played under me would happen. Think your infra-vision is all that you need? Well then I think that my traps should be nigh impossible to find but are marked with writing in common telling you exactly where they are and how to avoid them. Better yet lets have some undead attack you. Going all darkvison? Guess you can't see the color of that fungus on the wall that might only be scenery. I am not saying that I would be a jerk about it, but if you really decide to not bring even a single light source and I find out I will have some fun with you. If between the whole party you can't afford some flint and steel along with a couple torches then that is just pitiful.