Ozone vacuum-ultraviolet (VUV) ozone generators, employ a light source that generates a narrow-band ultraviolet light, a subset of that produced by the Sun. The Sun's UV sustains the ozone layer in the stratosphere of Earth. UV ozone generators use ambient air for ozone production, no air prep systems are used (air dryer or oxygen concentrator), therefore these generators tend to be less expensive. However UV ozone generators usually produce ozone with a concentration of about 0.5% or lower which limits the potential ozone production rate. Another disadvantage of this method is that it requires the ambient air (oxygen) to be exposed
The empire on which the sun never sets at the present time." In 1821, the "Caledonian Mercury" wrote of the British Empire, "On her dominions the sun never sets; before his evening rays leave the spires of Quebec, his morning beams have shone three hours on Port Jackson, and while sinking from the waters of Lake Superior, his eye opens upon the Mouth of the Ganges." Daniel Webster famously expressed a similar idea in 1834: "A power which has dotted over the surface of the whole globe with her possessions and military posts, whose morning drumbeat, following the sun and keeping company with the hours, circles the earth