Apparently nicotine is very sensitive to being degraded by sunlight(UV) so you’ll see warnings on bottles of ecig liquid to keep it in a dark place.
BUT the trend for tanks on ecigs is towards more clear glass, most tanks now totally expose the liquid to light. This is pretty annoying in a mild climate because year round half the time you use it you’re exposing it to sunlight.
Just how sensitive is nicotine? Should I paint most of the tanks with black nail polish or something?