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 slimline 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.

a. 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 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 plays 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.

b.  Cold Cathode Germicidal Tube

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.

c.  Slimline Germicidal Tube

Slimline germicidal tubes have similar electrical characteristics to slimline 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 slimline 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.

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:

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

b.  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.

c.  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.

d.  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 5,000 hours to 17,500 hours.

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.

High Output Ultraviolet Lamps

 These High Output Ultraviolet Lamps are unique in that they provide the highest amount of UV intensity available. 

They are  less sensitive to temperature variations and offer  minimal intensity loss over a wide range of temperature variances.

The following specifications detail one particular lamp. Other sizes available.

Lamp Characteristics

UV Output

 UV output is based on lamps measured after 100 hours of operation under lab conditions. These values are subject to wide variations under application/ field conditions.

  Protective Teflon Sleeves
  Germicidal UVC lamps must be fabricated from specialized quartz rather than ordinary glass, due to ultraviolet radiation (2537 angstroms) not being able to pass through most substances. Among the few that can be penetrated are quartz, from which all UVC lamps are composed, and certain plastics, such as Teflon.

Teflon can be extruded to form flexible non- seamed tubing of less than 1mm thickness and the inside diameter can be tailored to fit most UVC lamps (Slimline, cold cathode, and GPH preheat).

Such a sleeve will:
1. Contain the pieces in case of lamp breakage
2. Allow 90- 95% of the UVC germicidal energy to go through
3. Be resistant to lamp operating temperatures
4. Remain flexible and easy to clean

Available in different lengths to fit all UVC lamps, Fuller Teflon Sleeves have a Part No. of 6005/ Lamp P. N. 

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Fuller Ultraviolet Corporation
9416 Gulfstream Rd.
Frankfort, IL. 60423
Ph. 815-469-3301 Fax 815-469-1438
e-mail fulleruvcorp@mindspring.com