The sun sets at 4:11 this afternoon - for several months of the year the choice is between caching in the dark or not at all. Sometimes even during summer months, I find I have run out of daylight when there is still a good cache nearby*, or that I'm driving near a cache after sunset, and I decide to give it a try. Having said that, I have never actually gone out well-prepared (i.e. carrying a flashlight) and have generally relied on night-vision for getting to the cache location, and the backlight of my GPS (it's surprisingly powerful) for finding, logging and trading.
This has been a surprisingly successful strategy, and has added one or two points of difficulty to forest caches, as well as providing the unusual experience of wandering about in the forest at night. I have been told that I "wasted" one of the best caches in Ireland by doing it in the dark, but I have no regrets - it was quite a spooky and memorable experience to be so far from the road in the pitch dark, with deer crashing around nearby. Even the sound of a pigeon taking flight from a nearby tree can set your heart thumping, and I was once terrified by two dogs that came running past me at full speed.
* It's worth explaining that the density of caches in most of Ireland is far lower than seems to be the case in similarly populated areas of the US, so it's well worth taking extra trouble to find one, and "nearby" in this context could mean 20 miles away by road.