1. Erythemal:  which is commonly called UVB.  UVB light is found in the middle wavelength region of the UV spectrum and generally has a peak response at 312 nanometers.  The principal use of UVB lamps has been medically for the treatment of skin diseases.  There is some commercial use in the aging/degradation cycles for products.

1. Bactericidal:  which is commonly called UVC.  UVC light is found in the shorter wavelength region of the UV spectrum and generally has a peak response at 253.7 nanometers.  Its primary use is for the destruction of bacteria and other micro-organisms in air, liquid or on surfaces.

1. Ozone:  ozone is a gaseous allotrope of oxygen and is generated photochemically through ultraviolet lamps.  There are other ways to generate ozone such as corona discharge; however, for our purposes, we will talk about photochemical produced ozone.  It is produced as a gas at 185 nanometers in the UV spectrum.  Its principal use has been as an oxidizing agent and as an effective sterilant.

   2.  THE MYSTERIOUS INVISIBLE UNIVERSE CALLED MICROBIOLOGY

 Most everyone finds it hard to comprehend the diminutiveness of the microbiological world.  Telling someone there are lurking, unseen tiny monsters ready to do harm sometimes seems incredulous.  Yet, “out of sight, out of mind” is no excuse for tolerance of bacterical and other microbial contamination.  So, let’s explore this mysterious imperceptible abode of microbes. Microbiology is the world of unseen life; it’s a world of teeming microbial life comprising bacteria, mold spores, yeast and viruses.  Each of these tiny live organisms is a microbe, yet each is very different from one another. They can be located and identified by sophisticated microscopes, and upon measurement we find these microbes are very, very small, generally about 1/25,000^th of an inch. They reproduce at phenomenal rates.  For instance, if bacteria reproduction was left alone, we could be inundated.  Assuming a generation period of one bacterium of thirty minutes (these microbes reproduce by one cell dividing every 20 to 30 minutes) you could expect a bacterial mass weighing 10,000 tons in 36 hours!  Fortunately, environmental inhibitions and other factors control microbial epidemic activity, and we are not faced with this uncontrolled growth activity.  Nevertheless, some of these little “critters” play a very destructive role in contaminating air, liquids and product surfaces.  Means must be provided to control this contamination, and ultraviolet germicidal lamps provide the tools for control.  Later on in this booklet, there will be further discussion of microbial contamination. 

 3.  ULTRAVIOLET GERMICIDAL LIGHT…LETHAL; FATAL; DEADLY AND FINAL

 The killing of microbes is necessary in many situations.  For instance, the manufacturers of foods, pharmaceuticals and drinks are very aware of the legal and economic hazards of product contamination.  Microbial contamination creates a hazard in these industries, and it is simply not limited to these locations.  It is everywhere.  So, how to kill them? The destruction of micro-organisms is accomplished with the UVC rays directly striking them.  The kill ratio of course is dependent on time of exposure and the intensity of the UVC ray.  Thus, micro-organisms that come in direct contact can be readily destroyed.  However, if the micro-organism, whether it be bacteria or mold spores, is hidden below the surface, or if the microbe is not in the direct path of the rays, they will not be destroyed.  If any of these conditions prevail, alternative means such as the use of photo-chemically generated ozone can be used.  

 DESTRUCTION OF MICRO-ORGANISMS

 The killing of bacteria, viruses and other micro-organisms by ultraviolet is dramatized in these photographs, made through a microscope which magnified the paramecia 200 times.  Normal paramecium (A), after 30 seconds of treatment becomes distended (B), continues to swell by the weakening of the cell walls (C), and finally dies of internal explosion which bursts its outer skin (D).  

 4. UVC PENETRATION CAPABILITIES

 Penetrating, permeating, entering, perforating; no matter the description, it is an important function, and one that deserves careful consideration in designing UVC systems. UVC rays do not have great penetration ability on most substances.  Obviously, in the case of air, it has a very effective killing range.  Penetration is ineffective on such substances as meat, cloth, food, glass and other such “solid” materials. Consequently, air and surface irradiation are principal functions of UVC light.  On the other hand, the bactericidal treatment of a liquid is very effective depending, of course, on the conditions imposed by the liquid, the methods of handling it and the effective transmission of the UVC germicidal energy into the liquid.  In the case of disinfection techniques of granular materials and powdered solids, the theory is practically the same as for high absorptive liquids.  Actively stirring and agitating the surface of such materials is necessary to ensure an effective depth of agitation.  Equipment must be capably designed and operated to provide for the minimum UVC germicidal transmission. Section 11 discusses the use of an alternative method using ozone generated by UVC lamps.  Ozone, as a gas, has the ability to reach those hard to expose nooks and crannies.  It is an important alternative. 

 5. SKIN AND EYE PROTECTION

 Overexposure to UVC rays can cause a painful and irritating condition on skin surfaces and eyes of individuals.  The exposure time to cause such a condition varies with the sensitivity of each individual and also the length of exposure and intensity of the UVC source. The condition is temporary, and there are no known harmful physiological effects from the UVC rays except reddening of the skin and irritation of the eyes.  The condition is transitory and usually disappears within a day or two.  Plant life may also be damaged by direct or reflected exposure to UVC rays.  Transient dyes and colors may fade from prolonged exposure.The effects of overexposure to UVC must be dealt with in initial design considerations.  Safety features should be incorporated, lessening or eliminating the hazards of UV overexposure.  Personal protection can be achieved through the use of goggles, shields, gowns and other protective measures. 

 6. UVC TUBES – THE SOURCE OF ULTRAVIOLET

 Generally, there are three types of ultraviolet germicidal tubes; namely, the hot cathode germicidal tube, the cold cathode germicidal tube and the slim line germicidal tube.  They each have their salient points, and selection for a particular design must take into consideration the cognizant factors such as cost, tube life, intensity, temperature factors, environmental conditions, tube size and a host of other design elements. 

1. Hot Cathode Germicidal Tube

 Hot cathode tubes have the same electrical characteristics of a standard preheat type fluorescent tube.  They operate on typical preheat (starter type) circuits such as quick start or trigger start.  Tungsten filament electrodes located at the ends of the tube are coated with emission material and these electrodes govern tube life.  Tube life is somewhat nebulous because of certain factors.  The number of “on and off” cycles play a significant role in tube life.  In addition, the tube burning cycle is affected dramatically if operated in cold ambient temperatures such as cooling rooms, refrigerators, etc.  Hot cathode lamps are frequently hard to start at low temperatures. 

1. Cold Cathode Germicidal Tubes

 Cold cathode lamps do not have tungsten filaments for electrodes.  Instead, they are fitted with a firm solid cylindrical electrode at each end of the lamp. No starters are required since the lamp is started by means of high voltage input.  Interestingly enough, the cold cathode tube electrodes rarely wear out.  Thus, tube life is governed by the UVC transmission capability of the tube glass.  (Refer to Section 8 of this bulletin for more information.)  This type tube works excellently in cold atmospheres, and the high voltage starting features virtually assure instant starting even in freezing conditions. 

1. Slim Line Germicidal Tube

 Slim line germicidal tubes have similar electrical characteristics to slim line fluorescent lamps.  Like the cold cathode tube, it does not require a starter and uses high voltage for starting.  An interesting feature of this lamp is that it starts cold by the high voltage shock but operates with the electrodes hot.  Tube life is governed by the life of the electrodes.  The most popular of the slim line germicidal tubes is the G36T6 series.  It’s possible to operate the G36T6 at four different current levels of 120, 200, 300 or 420 milliamperes.  This allows four different UVC outputs. 

 7. DECIPHERING UVC EMISSION TERMINOLOGY

 There is certain nomenclature used in designing UVC systems, and knowledge of these terms will make your understanding much more complete and effective.  First of all, the UVC light source is emitted from a cylindrical tube with varying diameters, usually ranging from ½” diameter to 1” diameter.  These tubes can be selected from a variety of sources.  Refer to Section 6 for the types available. The emission intensity of a UVC germicidal light tube is usually expressed in a term called “microwatts per square centimeter” (mw/cm²), and this creates an aura of uncertainty to those not used to such a term.  So what does this actually mean?  Well, the maximum intensity provided by a single tube is at its surface.  So, if we calculate the surface area of the UVC lamp and only use that area which effectively emits UVC rays, we have established the “Effective Emitting Area”.  Simple mathematics shows that the surface area of a cylindrical tube is D L.  Expressed in another way, the following pictorial representation shows a cylindrical UVC tube being “unfolded” so that all of its surface area is in a plane.  This is known as the Effective Emitting Area:  Now if we envision effective emitting area as having a screen with squares 1 centimeter in size, the picture becomes clearer.  Each of these cm² areas now, for measurement purposes, emits a UVC lamp intensity measured in microwatts…thus, the term microwatts/ cm². UVC light decreasingly varies as the distance from the light gets greater.  There are some involved design considerations for calculation of true intensities at various distances.  For instance, many UV designers only consider the fact that intensity inversely varies as to the distance from the tube axis to the irradiated surface.  This is true, but only partially since as the distance goes past a point called “effective length”, there is a transition or change in the way the UVC intensity varies with distance.  These considerations must be used in UVC design to provide an effective system. In actual practice, it is possible to not only significantly increase the emitted UVC radiation by the use of well designed reflectors, but to control or contain the rays.  This is an especially important safety feature.

 8. UVC TUBE LIFE A surprising phenomena occurs when a UVC lamp is lit.  The phenomena is that you simply do not know by visual inspection if the lamp is operating satisfactorily.  A number of important factors are involved here: 

1. First, UVC energy is invisible to the naked eye.

1. Even though a tube may appear to be operating satisfactorily because it maintains a blue visible glow, the ultraviolet emission may be greatly decreased.  The blue visible glow is actually part of the visible spectrum.

1. Another feature of the tube is that after a significant amount of operating time, the glass can solarize.  This solarization prevents the ultraviolet from being emitted through the glass tube.

1. UVC tube life has a normal depreciation cycle.  During the first 100 hours of operation, the depreciation is rapid, and as a result, tubes are given an initial 100 hour rating.  Depending on the type of tube, rated life can vary from 5000 hours to 17,500 hours.

 Although the UVC tube has an effective operating life (see tube chart for details), it is of utmost importance that lamp maintenance be monitored with a UVC meter.  These types of meters are readily available for direct measurement or with remote sensing and monitoring capabilities. 

  9. CLEANING Metering of UVC intensity output is, of course, a most practical method to ensure proper output.  One of the major problems with UVC tubes is the possible effect of dust or dirt on the tube.  Depending on the environmental conditions, UVC tubes should be cleaned periodically.  This can be accomplished by manually wiping the tube with a commercially available tube cleaner or with a clean cloth dampened with alcohol (or ammonia) and water to maintain maximum ultraviolet output.  In liquid irradiation systems, specially designed wiper systems (either manual or automatic) are available.  The frequency of cleaning will vary with the conditions surrounding the design and environmental conditions.  The most important consideration is that design dictates and maintenance functions must be very explicit.  The importance of removing deposits of foreign materials on tubes cannot be overstated.  This type of deposit can appreciably reduce the transmission of the potent UVC rays. 

    The Ultraviolet Spectrum

 10. PRACTICAL USES OF UVC DEVICES

 Now, we finally get to the point where UVC can (and should) be used.  Obviously, not all microbial entities are pathogenic. There are many applications of ultraviolet germicidal tubes, and these applications may range from simple fixtures that direct UVC rays to a source of contamination to the more complicated UVC designs for specific applications.  The old adage which says “The Sky’s The Limit” is most apropos. In addition to the listed product possibilities, UVC is very applicable to other possibilities.  One area is animal protection.  Animals, like people, are quite susceptible to diseases transmitted by airborne microbial contamination.  UVC has been very successful in boarding rooms, laying houses, incubators, hatcheries, stables, pens, veterinaries and other such areas. Another area in which UVC is very appropriate is in personal protection.  UVC disinfection of air by means of room irradiation or air duct irradiation can protect personnel from possible infection due to airborne microbial infiltration.  This type of protection is applicable in numerous areas such as hospitals, clinics, medical and dental offices, clean rooms and just about any area where people congregate. There are numerous conditions which require or need non-chlorinated water for processing.  Some examples can include dairies, breweries, bottling plants and pharmaceutical houses.  There are many residential, commercial and industrial applications that need water (or other liquids) to be free of microbial contamination.  The use of ultraviolet germicidal liquid processors is most necessary.  Some other applications are shown in the following list. 

 GERMICIDAL APPLICATIONS

 11.   OZONE…THAT AWFUL WORD

 Ozone…you’ve heard it almost daily in the weather forecasts.  The average person thinks of it as a nasty substance, and that it is a major pollutant in our environmental involvement.  As usual, erroneous media reporting has cascaded the term “ozone” into a most unpleasant word.  So what is the real truth about this most remarkable substance.  What is it?  What isn’t it?  How does it work?  Does it work?  What does it do?  Let’s take a brief look at ozone. Ozone is a gaseous allotrope of oxygen, and it is known as a very strong oxidizing agent in addition to being an extremely effective sterilant.  It has been commonly used for many years as a water sterilant.  Many major cities use ozone for this purpose, amongst which include Moscow, Paris, Nice and, most recently, Los Angeles.  In fact, L.A. has the largest ozone generating plant in the world. Recently, ozone has been found to be extremely effective against microbial contamination of other materials.  Ozone has a unique advantage in that it is a gas and, as such, has the capability of reaching all those “nooks and crannies” to perform its microbial destruction in a most efficient manner. Ozone is efficiently generated by ultraviolet radiation having wavelengths below 200 nanometers and, most specifically, at 185 nanometers.  Ozone is excited by other UV radiation and is destroyed by ultraviolet emissions at 253.7 nanometers.  It is noteworthy that organic molecules are also excited by ultraviolet energy across the spectrum.  The most efficient design of UVC equipment uses a combination of wavelengths to achieve a balance between ozone generation, decomposition and molecular excitation. Ozone is a most useful tool by itself, and when used in conjunction with UVC, the overall decontamination process works synergistically. 

 12.   GERMICIDAL LAMPS

 Fuller germicidal lamps in standard designs use Vycor quartz and Corning 9823 glass or equivalent.  On special requests, lamps can be engineered to use ozone free quartz, Suprasil or other special glasses.  Germicidal lamps having quartz, Vycor 7912 or Suprasil glass tubes emit various amounts of ozone.  As a matter of interest, lamp bases can be furnished in standard plastic or ozone resistant ceramic on cold cathode and slim line lamps.  For full product line and description, refer to Fuller Lamps Bulletin 77. 

 13.   GERMICIDAL ULTRAVIOLET AND ITS INFLUENCE ON INFECTION Infection, a dreaded word, is actually the spread of disease-producing organisms called pathogens.  Pathogens live nearly anywhere in our everyday environment; air, water, surfaces and within the body in body fluids.  Obviously, there are certain locations and certain occupations that have a higher risk, and this is usually found in the medical and dental environment.  However, wherever people congregate, the chance of infectious transmission is highly significant. The use of germicidal devices to reduce or eliminate the threat of microbial transmission is an efficient, effective environmental method, whether the transmission is via airborne, waterborne or on surfaces.  Pathogens must enter the body for a person to become infected.  This transmission enters the body most commonly through cuts or scrapes in the skin or mucous membranes and also by direct transmission to mouth, eyes, nose or aspiration into the lungs.  Microbial contamination of food, water or other liquids also provides another causative pathway for infection. Fuller UV germicidal devices are designed to meet the threat of just about any type of microbial contamination in almost any environment.  We suggest contacting a Fuller trained engineer to discuss your particular problem.  

PREHEAT TYPE

COLD CATHODE TYPE

SLIMLINE

AMALGAM LAMPS