Williams FireSights are one of the new kind of pistol sights, which are using fiber optics, to produce a very strong dot image. The dots are very visible, even in bright sunlight (actually, the qualities of the fiber optic make the dots brighter, in strronger lighting conditions), but I am not sure as to how visible the are in near darkness. Of course, they should be totally invisible in absolute darkness, in contrast to the tritium sights, but this is only an academic issue, as you do not need your sights, when you can not identify your target. Since the manufacturer's pictures did not show the dots properly, here is another picture for you.

This picture is taken by my good friend Tom Cortese, after he installed these sights on his own M-1911. Thanks Tom.