Narration

When visible light is replaced by an ultraviolet light source, the glass casts a dark shadow on the fluorescent background, because glass absorbs ultraviolet light. Ozone coming out of the tube also casts a shadow. Whenever the valve is turned on, a cloud of ozone comes out of the end of the tube and its shadow can be seen. Absorption of ultraviolet light by the ozone is the same process that occurs in the stratosphere, where ozone absorbs ultraviolet light coming in from the sun. Without this ability of ozone to absorb some of the ultraviolet light, life on earth would be considerably different.