Three views of the same flasks of fluorescent rhodamine dye. At the far right is a picture of how the flasks look under regular room lights. In the middle, the scene is illuminated by a UV-emitting flashlight (otherwise known as a blacklight). Under this strong, high-energy illumination, the fluorescence from the dye is much more evident. Finally, in the picture at the left, I’m illuminating with the UV flashlight, but using a filter in front of the camera to get rid of the light from the UV flashlight, so only the fluorescence remains.