Inks, both visible and invisible, that fluoresce under black lights.

Printing inks that both emit and reflect light. Generally, these inks are brighter and more opaque than traditional inks. Using one or more fluorescent inks can actually brighten a printed image - especially four-colour process printing on uncoated stock. On the down side, fluorescent inks are not colourfast and will fade in bright light and sunlight over time. They can also have a negative effect on dot gain and trapping, making the printing less sharp and without as much detail.