I have always been told that it is best to keep ink in a dark, cool place with the cap screwed on as tightly as possible. I don't know how long it would take or how much sun light would be on the ink but I have heard of people saying their ink faded. It is important to close the bottle as tightly as possible to prevent the water in the ink from evaporating leaving you with an unusable colored slush. Taking all of the possible precautions, the ink should be able to last quite a while. I know of people who use ink that is 40 or more years old. If some ink has evaporated, it is sometimes possible to add water and get back useable ink.
If you use the ink quickly (finish the bottle within a year) it probably doesn't matter, but if you want to use the bottle for a long time you might want to put the ink out of sunlight to be safe.
Sadly none of this is actual facts but only things that I have been advised of through others.
-Jesse