From time to time someone puts one of their posters up where it gets a lot of sun, and after a while the poster fades. This can also happen under some fluorescent lighting, especially when the poster is very close to the light. Ultraviolet light is the culprit, it fades lots of things over time, including the inks that have been traditionally used in large format printing.
Much of the newer equipment on the market has what are called UV inks, meaning they are designed not to fade in sunlight. They are good for 5 years or more indoors. A lot of what we print uses UV inks these days, but not always. That’s because we have several generations of equipment here, and frankly, we like the color results we get from some of the older equipment. And, when we get very busy, we may run your print on an older machine to get it out the door the same day. Which I guess is a way of saying that when push comes to shove, we worry more about getting your poster to you on time.
If you plan to put your poster where it will get direct sunlight, ask for UV inks in the special instructions of your online order. It adds a little to the cost, but your print won’t fade.