Appl icat ions οί H i g h - V o l t a g e Fluorescent Tubing

J U L I A N A . McDERMOTT ASSOCIATE AIEE

H IGH-VOLTAGE fluores­cent tubing is the logical

development of the simple cold-cathode low-pressure dis­charge tube. Transformers, glass, and wiring methods have not materially changed bu t the fluorescent coating has been added to the inside walls of the tubing. Advances have been made, however, in the techniques of use, and the inherent characteristics of the light source offer wide possibilities for future exploitation.

CHARACTERISTICS

Electrical. High-voltage tubing is operated with a transformer having constant current characteristics ob­tained through the use of a magnetic shunt . From 1,500 to 15,000 volts may be used. Tubes are connected in series. Under the proper conditions more than 100 feet of tubing may be connected in series and operated from a single transformer.

Tube currents range from 8 to 250 milliamperes. De­vices have been developed and are gradually coming into use tha t will increase the safety where high voltages and currents are used. These include spark-gap thermal re­lays which shunt out defective tubes or cut off the current, and magnetic devices operating on the transformer which interrupt the primary circuit instantaneously when an open circuit occurs in the secondary.

Dimming is accomplished by voltage control, either by primary taps or by primary resistance methods. Those tubes employing mercury are best adapted for this purpose because of the lesser tendency toward flickering with lower voltage and current values. There are limits through which certain types of tubes may be dimmed and careful consideration must be given as to electrodes and processing for any particular service.

Tubes may be obtained having wat tages of from 1 y 2 to 17 watts per foot over-all.

Shape and Size. Tubes having outside diameters of from one-half inch to one inch may be obtained commer­cially. Lengths generally are limited to 12 feet on account of difficulties in handling and processing. However, it is recognized t ha t longer lengths are desirable, because the electrode losses are considerable and the efficiency of longer tubes would be higher. Tubes may be bent to sharp curves or other irregular shapes.

Color. A wide range of colors is available, including numerous whites, green and blue which result from mer-JULIAN A. MCDERMOTT is with the engineering division of the bureau of archi­tecture, Public Works Department , City of N e w York, Ν . Y.; he formerly was chief engineer, Claude N e o n Lights, Inc., Long Island City, Ν . Y .

cury-vapor discharges with mixed argon- and neon-carry­ing gases, and salmon, rose, and pink which result from neon - gaseous discharges. Those tubes employing mer­cury are subject to serious de­preciation in cold weather, bu t a green tube and a white one have been developed which operate at fair efficiency and

which do not employ mercury. Properly processed tubing should have no start ing difficulty in cold weather and should show no dark spots or discoloration during its life.

Efficiencies and Life. Tubes of this type can be made t h a t will operate for very long periods. Many records are available of installations operating for 16,000 hours or more without the replacement of any sections.

Efficiencies are somewhat difficult to establish because of the great variation among tubes obtained from different sources. A number of manufacturers are merchandising

Figure 1 . Plastics and high-voltage fluorescent tubing were combined to provide an effective sign for the Florida building

at the N e w York W o r l d s Fair

Advances in application of high-voltage fluores­cent tubing are making it increasingly useful not only as a sole light source but also as a comple­ment to other sources. Presented here is the scheduled conference discussion on the subject given at the A I E E 1 9 4 1 winter convention, sup­plementing other scheduled discussions from the technical session and conference on fluores­cent lighting which appeared in the June issue.

McDermott—High-Voltage Fluorescent Tubing JULY 1941 327

is manufactured for the specific purpose of illumination, where longer lengths of tubes are used, and where auxiliary equipment designed for this specific purpose is included.

For most illumination calculations the average values mentioned will suffice, bu t where greater accuracy is es­sential a s tudy must be made to determine the most desir­able values for the length of tubing, gas mixture and pres­sure, life of electrode material, tube diameter, coating material, and processing.

APPLICATIONS

The more general uses to which high-voltage fluorescent tubes have been pu t include advertising, illumination, photography, and specialty purposes such as aviation signals and colorimetry.

Advertising. The widest field of use has been for signs Figure 2. The use of curved tubes produces interesting and where high-voltage tubing has been substi tuted for red

satisfactory decorative fixtures neon, helium-white, and blue and green mercury tubing. The tendency is for this type of tubing to supersede all the previous tubes used for advertising. I t is more efficient,

coated-glass tubing. This is fabricated into sections and has a greater visibility, and is more resistant to the effect processed by thousands of manufacturers who have con- of cold weather than the ordinary mercury blues and siderable variation in procedure and in general little engi- greens; it is more efficient than the helium type of tube ; neering control. The result is t ha t the products differ and many municipalities are giving consideration to pro-considerably in characteristics. hibiting the use of red neon and green tubing for signs be-

The tubing used for sign work must be so coated with cause of interference with traffic signals, fluorescent powder tha t adherence is maintained although The high light output of this tubing has permitted the sharp bends are made in the glass. This generally is not wider use of translucencies and plastics to obtain more conducive to obtaining maximum efficiency. The wattage effective advertising displays. A typical installation was consumed in any section of tubing is the total of the elec- the "Flor ida" display a t the New York World's Fair trode losses plus the column consumption; hence the (figure 1). Four deep blue tubes were arranged behind longer lengths of tubing are most efficient. The size of laminated plastic sheets forming the name. The daytime tubing in greatest use is 15 millimeters in diameter and is effect was tha t of a solid block of letters, so t h a t the archi-employed with transformers rated a t 60 milliamperes tectural features of the building were not impaired. At short-circuited and operating normally a t 48 milliamperes. night the deep blue color offered a striking contrast to the The over-all average wattage of mercury tubing operating incandescent flood lights. Other such uses include the under this condition is 7 wat ts per foot.

Tests on samples 3 feet in length gave the following efficiencies:

Lumens Per Watt

W a r m w h i t e 28 Cold wh i t e 26 Yellow wh i t e 32

Efficiencies were established after 200 hours of operation. At tha t t ime the initial drop in intensity had taken place. Samples of many white shades had indicated an additional drop in intensity of 30 to 40 per cent up to 5,000 hours. After this life is obtained the depreciation curves usually flatten out, showing only a small variation. Test samples indicated a total loss of 50 to 60 per cent over 12,000 hours.

I t must be repeated again that these are average values for good tubing manufactured essentially for sign pur­poses, and operated with transformers manufactured for t ha t purpose. Higher Figure 3 . Fluorescent tubing is used for ceiling coves and showcase lighting efficiencies are available where tubing in this haberdashery

328 McDermott—High-Voltage Fluorescent Tubing ELECTRICAL ENGINEERING

Figure 4 . Cove lighting and staircase illumination in this lol of high-voltage tubing

edge-lighting of letters formed of t ransparent plastics or glass, and the lighting of silhouette block letters mounted on walls.

Considerable application has been found for these fluo­rescent tubes in portable signs having interchangeable letters. A high-frequency vacuum-tube oscillator is used instead of the transformer, and the tubes may be operated in multiple. Connections are made to the tubes through metallic plates of suitable capacity mounted in the bases of the letter holders. In this way extreme flexibility is ob­tained.

Illumination. Fixtures employing high-voltage tubes have begun to appear on the market . Generally these take decorative forms. Bent tubes may be made into an infinite variety of pat terns.

In figure 2 the elementary forms of concentric rings are adapted to custom-built fixtures. Numerous installations have been made where the tubes, usually of various colors, are incorporated in fixtures or are mounted on the ceiling to form a decorative pat tern . Generally a number of colors is included so tha t both mercury and neon dis­charges are obtained. In this way a more complete spec­t rum range is obtained and the effect of the resultant color on fabrics or food is satisfactory.

The use of combinations of colors to get the most accept­able light for the examination of clothing is shown in figure 3. Three white tubes and one neon gold tube were lo­cated around the ceiling cove to provide a high level of general illumination in the sales area. In addition tubes one-half inch in diameter were located along the front edge of the showcases and in vertical bars on the wall cases

to provide inconspicuous bu t effective background illumi­nation.

The use of tubes for a specific illumination problem where space is a t a premium is well illustrated in the lobby installation shown in figure 4 . Small - diameter tubing illuminates the stair from its position under the hand rails. The cove above is illuminated with a tube shaped to fit the wall curvature. Turnbacks are made in the lengths ol tubing so tha t all shadows from connections are eliminated.

A high-intensity installa­tion is shown in the exposition building (figure 5). Tubes 12 feet in length formed a huge grid on the ceiling and pro­duced 35 foot-candles on the floor. Floor displays are emphasized by incandescent

f illustrate the flexibil ity d o w n l i g h t s r e C e s s e d into the ceiling. Tubes operated at 120 milliamperes were installed so t h a t joints between sec­

tions were unnoticeable. Where long lengths can be used this type of installation is extremely effective and efficient.

Probably the most effective and exciting uses to which high-voltage tubing has been pu t are those in which a number of colored tubes are installed in coves for back­ground illumination and incandescent spotlights are used to emphasize objects of special interest. Wi th this me­dium the designer can a t last "paint with l ight" and the whole feeling of a room can be changed by the snap of a switch. A number of such installations have been made in showrooms, night clubs, and stores, using red, green, blue, and orchid tubes. Usually the tubes are operated a t about 3 wat ts per foot and the cost of operation and re­placement is small.

The small-diameter tubes are also useful where projec­tion is desirable and they may be incorporated in optical systems where fluorescent tubes of larger diameter would be ineffective. This method has been used for high-bay factory illumination and for high-cove indirect-lighting systems where Alzak parabolic reflectors were used in the cove.

All the installations mentioned were designed before the revision of the National Electrical Code in November 1940. New regulations were established in t ha t issue of the code whereby the space requirements for electrodes were increased and the installation conditions were in gen­eral made more stringent. Although revisions of this code have been discussed, i t is effective a t this t ime and the greatest consideration must be given to all designs to as­sure agreement with its requirements.

Photography. A considerable use has been found for

JULY 1 9 4 1 McDermott—High-Voltage Fluorescent Tubing 329

for the production of near-ultraviolet light. The possible specialized uses are evidently many and await only the familiarity of designers with the available features.

TRENDS

The trend of this whole field has been forward. However, the industry in the United States owes a large debt to French research and for the pres­ent t ha t is ended. The manufactur­ing methods generally being followed a t present are purely those of a craft. I t has not been practicable to intro­duce machine-production methods, and without these the uni t costs are relatively high. Reports from South America and Australia indicate in-

r _ A I . . . ι · ! creasing application of this type of F.gure 5 Architecture and lighting were strikingly co-ordinated in this ex- e q u i p m e n t j d e s p i t e w a r t i m e c o n d i t i o n s . position building illuminated by a huge grid of high-voltage fluorescent tubing J t s p l a c e ^ a d v e r t i s i n g i s s e c u r e b u t

whether widespread advances will con­tinue in other fields of applications de-

high-voltage fluorescent tubes for enlarging and similar pends upon whether the manufacturers can adapt them-applications in photography. Usually the tubes are aged selves to the conditions facing them and compete against so tha t the operation takes place on the flat pa r t of the de- or more fully complement other light sources. Re-preciation curve The result is t ha t effects can be du- search and development are prime requisites to the solution plicated accurately at subsequent dates. Blue tubes are of this problem and the effect of such efforts is already be-used because of their high actinic value. Frequently the ing felt. Special tubes, processed to give satisfactory ef-units are equipped with dimmers so tha t the photographic fects upon foodstuffs and meat products have been used speed is variable. in refrigerator display cases in considerable quantit ies.

Specialty Uses. Among the many specialized applica- Protective devices t ha t eliminate the dangers of shock and tions to which high-voltage fluorescent tubes have been damage inherent in high-voltage systems have been devel-adapted are battery-operated aviation and marine signal oped and may expand tremendously the applications of systems, colorimeters for chemical determination, and units this lighting medium.

Low-Vol tage Cords Eliminate Shocks

USE of extension cords with special 50-watt t rans­formers to reduce the supply voltage to six volts,

by the Public Service Electric and Gas Company of New Jersey, has eliminated the electric-shock hazard in the use of portable hand lamps in damp locations, accord­ing to a recent number of Public Utilities Safety issued by the National Safety Council, which reported as follows:

' 'There seems to be a belief among workmen t h a t 110 volts is not harmful and can produce fatal shock only in cases where a man has a weak hear t . This is not t rue . Tests have been conducted which show t h a t when an electrical circuit is completed through a wet contact , any voltage in excess of 12 volts is dangerous.

"Realizing the hazard t h a t existed when work was per­formed in wet or d a m p locations t h a t provided a perfect ground for the 110-volt circuit should extension lamps become defective, the electric generation depar tmen t of the Public Service Electric and Gas Company in 1928 de­

cided to have one of the local manufacturers design and develop a 110- to 32-volt 50-watt transformer. During t h a t year, 1928, all 110-volt extension cords were replaced with the new 32-volt transformer.

" I n 1939, however, as a result of further experimenta­tion, this transformer was rebuil t so t h a t its secondary voltage was reduced to 6 volts, which is recognized as an absolutely safe minimum. I t is now possible to procure 6-volt lamps with the s tandard base. Low-voltage t rans­formers of this kind are being used extensively about the proper ty to eliminate the electric shock hazard.

"Cases of electric shock and accidents resulting in falls from shock are recalled which, a l though in themselves were not serious, indicated the potential hazard t h a t was continuously present. The use of the lower voltage has completely eliminated the hazard, inasmuch as there has not been a single case of electric shock reported since the transformers have been in use ."

330 McDermott—High-Voltage Fluorescent Tubing ELECTRICAL ENGINEERING