While it works well as a screen saver, there is also an included mini-app which is nice for low-light situations you might find yourself in. I like the white text on black effect, which is really great when sitting and reading in the dark as I do sometimes to keep the light from disturbing anyone (like a sleeping baby or wife).
What is Black Light? Well, basically it inverts the color on your system. It allows a fair amount of customization in the settings for exactly how it does this, how frequently, etc. In short, it makes your screen look like the light source is a black light (with options to randomly shift the colors). The effect is pretty cool, especially if, like me, you are on the computer a lot at night in low light and don’t like screen savers that make the screen real bright. [Apple-X.net]