the curtains are closed in the UV ROOM, outside light is excluded
except for that coming through a glass panel overhead. In the room
are various plastic objects that have fluorescent colors. The glass
above allows UV light to pass through, while blocking visible light,
causing the objects to glow. The UV light seen here is always around
when the sun is up, but normally is not noticed because the visible
light is so bright that it drowns it out.