ULTRAVIOLET LIGHT — GERSHENFELD 213 



partments was costly and not practical. To keep the heat directly 

 from the material being treated, the generators had to be placed at 

 relatively long distances from them, resulting in a marked decrease 

 in the effectiveness of the shorter and highly germicidal radiations. 

 In other types of generators, there was a large output of high con- 

 centrations of ozone and nitrous oxide, which were objectionable, as 

 they affected humans and inanimate objects being treated. The 

 newly introduced equipment or so-called ultraviolet lamps have 

 evolved from a careful segregation of different wave lengths and 

 the elimination of other short-wave radiations that are valueless as 

 bactericidal agents and even undesirable. 



By a simple and rapid method for measuring ultraviolet radia- 

 tion, a better understanding of the action of short waves on germs 

 has become possible. In fact it was found that radiations or short 

 waves generated at the 2537 Angstrom unit region of the spectrmn 

 possessed the greatest sterilizing or germicidal power. The intro- 

 duction of this new equipment with an effective ultraviolet lamp and 

 the practical application of selective bactericidal ultraviolet waves 

 or radiations developed into a process known by many as the rent- 

 schlerizing process or rentschlerization. These terms are taking their 

 place today with the term "pasteurization" named after Pasteur, a 

 process in which moist heat is used to render disease-producing bac- 

 teria innocuous. 



ULTRAVIOLET LAMPS 



Many of you are familiar with or have seen sun lamps or so- 

 called health lamps. These sun lamps generate waves or radiations 

 which vary in length from 2800 to 3200 Angstrom units. Accordingly 

 they supply only long ultraviolet waves and practically of the same 

 intensity as we get from sunlight under ordinary conditions. In fact 

 the glass used in sun-lamp bulbs will not allow the passage of radia- 

 tions of wave length shorter than 2800 Angstrom units. Sun lamps 

 therefore do not transmit ultraviolet radiations which are germicidal. 



The effective ultraviolet lamps used today to generate radiations 

 of value for the destruction of bacteria depend upon a carefully 

 planned type of vapor source, emitting controlled and selective bac- 

 tericidal ultraviolet radiations. They consume a minimum amount 

 of power and radiate a minimum amount of heat energy. They are 

 almost identical in operation with the fluorescent lamp, except that 

 fluorescent powder is absent. As the current flows from electrode to 

 electrode through mercury vapor (to which other gases are frequently 

 added) , very little visible light is produced, but most of the output of 

 its energy is concentrated at the 2537 Angstrom region of the spec- 

 trum. At least 80 percent of the radiant energy is crowded into ultra- 

 violet radiation at this region which provides the most effective germi- 



