CA1299450C - Method and apparatus for coating fluorescent lamp tubes - Google Patents

Abstract

METHOD AND APPARATUS
FOR COATING FLUORESCENT LAMP TUBES

ABSTRACT OF THE DISCLOSURE
Method and apparatus for electrostatically applying phosphor coatings to the interior surface of fluorescent lamp tubes includes equipment for applying an electrical charge of one polarity to the glass wall and electrical charge of the opposite polarity to the phosphor particles to cause the phosphor particles to adhere to the glass surface until the particles can be heated to bond them to the interior surface of the glass by lehring. By using electrostatic deposition the lehring may be done at a lower temperature than is required with conventional phosphor deposition using organic binders so that U-shaped fluorescent lamps do not experience distortion from the lehring temperature.

Description

o ~ 1 - LD 9325 METHOD ~ID APPARATUS
FOR COATING FLUO~ESCENT LAMP TUBES
__ _ BACKGROU~D OF THE I~7E~TIO~
_ _ _ 1. Field of the invention.
This invention relates to the manufacture of fluorescent lamps, and, more particularly, to a method and apparatus for applying a layer of particulate material to the in~ide of a fluorescent lamp bulb by electrostatic deposition.

2. Description of the prior art.
In the prior art techniques for manufacturing fluorescent lamps, phosphor coatings are typically applied a~ a suspension of particulate material in a slurry including an organic binder. The organic binder serve6 the function of holding the phosphor particle~
to the glass bulb ~urface during the manufacturing of the bulb. A~ter application of the phosphor coating, the bulb~ are lehred at a high temperature to vaporize the oryanic binder and bond the phosphor particle~ to the gla~ bulb ~urfaee and to other phosphor partiele~
to form a uniform, well-bonded eoating on the ~luoreseent lamp bulb. ~hie technique requires heating of the lamp bulb to a temperature which would eause the lamp gla~s to ~often. To prevent distortion of the pluoreseent lamp bulb, straight line fluoreseent lamps are eonventionally rotated during the lehring process ~o that the gravitational effects are averaged and the lamp maintains a straight shape.

~9~5~

U-shaped fluorescent lamps having both ~ets of lamp terminals at the same end of the lamp raise a difficulty with respect to lamp coating and lehring which is not experienced in manufacturing straight S fluorescent lamps. In prior art techniques of manufacturing U~haped fluorescent lamps, the phosphor coatings are typically applied as water suspensions containing organic polymer binders which act a~
di6per~ing agent~ to provide ~mooth coating appearance. After the coatings have been applied, the binders must be removed prior to sealing of the lamp and filling with the typical fluorescent lamp atmospheres, because the organic materials of the binder are incompatible with the fluorescent lamp atmosphere and tend to cause darkening and 10~6 of lamp efficacy in lumens per watt over the life of the lamp.
The binders typically are removed by baking at elevated temperatures, i.e. lehring, for a sufficient time to vaporize the binders. When folded fluorescent lamp tubes are subjected to lehring temperatures typically u~ed for lehring lamps coated with water-based organic binder coatings (600-630C), the glass can soften resulting in distortion of the glass tube due to gravity. It is impractical to roll the folded tube during the lehring proce6s to average gravitational effects, and, therefore, lehring must occur at lower temperature~. However, lower temperature lehriny significantly lowers lamp efficacy and maintenance due to the incomplete removal of the organic binder material~. In one prior art technique for manufacturing U-shaped fluorescent lamp~ a tin oxide ~tarting ~trip is applied to an interior ~urface of the fluorescent lamp extending generally from one electrode around the bend of the lamp to the opposite electrode ~2~
_ 3 _ LD 9325 in order to assi~t in starting of the lamp. If this coating is applied prior to lamp bending, difficulties are e~perienced in maintaining electrical continuity of the starter strip following bending of the gla~s tube due to the strain on the glass and therefore on the ~tarting strip during bending. Thexefore, the starting strip is typically applied after the glass tube has been bent into the desired U-shape. A difficulty experienced when using tin oxide as the starting strip results from the use of an in~ulating barrier coating on the tin oxide coating to overcome the poor adherence of phosphors to tin oxide and the tendency of the tin oxide to darken with exposure to the atmosphere inside the fluorescent lamp. To improve adherence of pho~phor materials to the tin oxide coating, certain types of borates, e.g. calcium borate, are included within the binder material. Removal of the binders from the lamp following deposition of the phosphors requires a ~till higher lehring temperature when additional borate additives are used, which increases the risk of sag in the U-shaped lamps. To overcome these limitations in the manufacturing of U-~haped fluore~cent lamps, a technique of applying phoRphor coatings and bonding the coatings to the lamp glass without requiring high temperature lehring iB required.

SUMMARY OF T~IE INVENTION
~ n ob~ect o~ the present invention iB to provide a method and apparatus or applying phosphor coatings to the interior surfaces of fluorescent lamp tubes without requiring the use of binder materials who~e removal from the lamp requires high temperature lehring. A more specific object of the presentinvention i~ to provide an electrostatic coating technique for applying pho~phor layers to the interior surfaces of a U-~haped fluorescent lamp.
Accordingly, the present invention includes an electro~tatic coating apparatus having one electrode positioned outside the glass tube and at a predetermined position relative to a pair of ~econd electrodes placed in~ide the glass tube during the coating process, each of the ~econd electrodes having a nozzle attached thereto with passages therethrough for the aelivery of phosphor coating material to the interior of the glass envelope and a tip for forming a corona; and connections to a high voltage d-c electrical power supply for applying ~oltage of a first polarity to the first electrode and voltage of a second polarity to the second electrodes; such that a field is created between the electrode tips which causes the glass tube to become electrically charged with one polarity and the particles of phosphor material to become oppositely charged, ~o that the phosphor particles are attracted to the interior surface of the glass tube and adhere thereto.

BRIEF DESCRIPTION OF THE DRAWINGS
Further objects and advantage3 of the present invention together with its organization, method of operation, and be~t mode contemplated may be~t be understood by re~erence to the following de~cription taken in conjunction with the accompanying drawings in which:
E'IG~ 1 is a ~chematic elevation view of a fluore~cent lamp coating apparatus according to the present invention;

FIG. 2 i~ a ~chematic elevation view, partly in section, of an apparatu~ according to the preRent 5~
~ 5 - LD 9325 invention for applying coatings to the interior surface of fluore~cent lamp tubes;
FIG. 3 is a ~chematic partial cross-sectional view of a nozzle for the coating apparatus of the present invention, anlarged to illustrate details thereof;
FIG. 4 is an elevational view, partly in section, of an alternative embodiment of the coating apparatus of the present invention;
FIG. 5 is a greatly enlarged schematic view illuetrating the fluorescent particles electrostatically bonded to the surface of a fluorescent lamp tube;
FIG. 6 is a greatly enlarged schematic view of a glass tube wall illustrating the completed bonding of phosphor particles to a lamp glass surface according to the present invention; and FIG. 7 is a block diagram illustrating the phosphor depo~ition method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIME~TS
A~ shown schematically in FIG. l, the apparatus of the pre~ent invention comprises equipment for coating the interior surface of a ~luorescent lamp glass tube while the tube iB suspended in a suitable holding device (not shown). ~he coating apparatus includes a high voltage electrode lO and a pair of phosphor supply tubes 26, 28 secured to a movement mechanism 25 for moving the electrode lO and supply tubes 26, 28 relative to the glass tube 20 at a controllable, con~tant rate. ~he movement mechani~m may include hydraulic, compre~sed air or electric motor means 27 to provide the controlled movement. The electrode lO and ~upply tubes 26, 28 are secured to suitable holders 23 for movement together during pho~phor deposition. As shown in more detail in 5~

FIG. 2~ a high voltage electrode 10 co~pri6ing conductive rod 12 and conductive tip member 14 i8 disposed 60 that the points 16, 18 at the respective ends of the conductive member 14 are in close proximity to the glass tube 20 but are not in contact therewith.
The rod 12 is connected via a ~uitable conductor shown 6chematically as 22 to a high voltage d-c power supply 24. The present apparatus further includes supply tubes 25 and 28 for receiving via tubee ~5, 27, respectively, a mixture of dry air and powder from a powder supply hopper 29 of conventional design, such as a fluidized bed, and conveying the mi~ture of dry air and powder to the interior 30 of the glass tube 20 for coating the interior surface 32 thereof. The nozzles 34 are both of a similar co~struction, one of which is shown enlarged in FIG. 3. The tube 26 is connected to a nozzle 34 for example by threads 38. The nozzle 34 includes a plurality of paesages 39 cut through the closed end wall 47 at a predetermined angle with respect to the nozzle centerline 40 to concentrate the phosphor powder in the corona region 42 surrounding tip 44. The angle ~ is determined experimentally to provide optimum powder flow from the nozzle past the tip 44 and through the corona region 42 into the interior of the glass tube for deposition upon the surface 32, 6hown in FIG. 2. The angle ~ determines the distance of travel of the phosphor particles before deposition on the glas~ surface. The pa8sages 39 are typically 50-100 mil~ in diameter, sub~tantially larger than the particle size of the phosphor being deposited. The passages 39 may be cut with a slight spiral to cause the phosphor particles to swirl as they pass over the tip. The tube 26 may be a copper tube having a plastic coating to prevent erosion of the tubing by fluorescent phosphor particles supplied to _ 7 _ LD 9325 the interior of the lamp, or alternatively the tube 26 may be a stainless steel tube requiring no inner lining. The tip 34 is preferably of ~tainle6s ~teel.
The rod 12 and tip member 14 are preferably of copper or other ~uitable conductive material. Although the conductive member 14 is shown to be in the plane of the U-shaped glass tube 20, the rod 12 and tip member 14 may be offset, e.g., above the plane of the paper as shown in FIG. 2 but in a plane generally parallel to the plane including the re3pective centerlines 40 of the tips 44, so that it may be positioned nearer the top 21 of the bend in the glas~ tube 20. By using the offset position, the tip member 14 may be positioned to ensure deposition of phosphor powder over the entire suxface of the curve in the lamp if required for particular phosphors.
An alternative embodiment is illustrated schematically in FIG. 4 for the application of phosphor coatinys to a different type of U-shaped fluorescent lamp. The lamp tube 50 is a glass fluorescent tube used in twin-tube lamps of the type sold by the General Electric Company under the trademark MOD-U~LINE~ having a sharp U-bend and smaller diameter, typically T-5, than the lamp shown in FIG. 2. For coating a lamp of this configuration the central rod 52 has a tip 54 attached thereto generally aligned with the axi~ 56 of the rod 52. The pair of ~upply tubes 58 and 60 are configured to have bend~ 62, 64 and 66, 68, respectively, to po~ition the supply tubes properly for ingertion into the legs 74, 76 of the U-shaped lamp tube 50. The supply tubes have nozzles 70, 72 of a con~truction similar to nozzle 34, described above, but of smaller diameter connected respectively thereto.
The materials of the rod 52 and the supply tubes 58 and 60 and the nozzle 70 and 72 are as described above with 5~

respect to the ~mbodiment of FIG. 2~ The rod 52 and tip 54 could be offset from the plane of the glass tube 50, rather than being in ~he plane of the tube 50, so ~hat the tip 54 could be positioned adjacent the U-6haped bend rather than within the ~-shaped bend.
The tip 54 could be provided by turning the tip member 14 perpendicular to the plane of the glass tube and positioning one of the tips 16 or 18 in close pro~imity to the bend of the tube 50 of FIG. 2.
The present invention provides a method of phosphor deposition as shown in the block diagram of FIG. 7, as follows: the glass fluore6cent tube is bent into the U-shaped configuration while heated. While the glass tube is still hot, it i8 loaded into a suitable lamp holding mechanism for deposition of the phosphor coating6. Alternatively, the bulbs may be allowed to cool and then be reheated. The heating removes moisture from the surface of the glass tubes and thereby reduces 6urface conductivity, which would interfere with the application of charge to the glass surface. The supply tubes 26 and 28 are inserted into the legs of the U-~haped lamp, and the electrode tips 16 and 18 are positioned adjacent the glass tube wall and slightly above and generally adjacent the position of the ~ips of the nozzles. The 8upply ~ubes 26 and 28 are connected to electrical ground. The power ~upply 24 connected to the rod 12 ~upplies a D.C. voltage in the range of 20 to 50 kv. The exact settirtg for a particular deposition i8 establiehed by raising the voltage to a level at w~lich breakdown occur~ in air and then reducing the voltage level slightly to avoid arcing. q~tis ~pacing i~ typically in the range of about 0.50 inch to about 2.00 inches. A supply of dry air or other suitable gas i8 provided to the pho~phor feed hopper to entrain particulate matter in a ~tream _ g _ LD 9325 flowing vertically upward through the tubes 26, 28 into the bight of the glass tube. The phosphor particles are charged as they pass through the corona region 42 The phosphor particle 6ize is typically 3.0 to 15.0 microns plus or minus 15 percent, which is standard for fluor~scent phosphor particle size. The passages 39 are thus much larger in diameter than the particles and do not significantly affect particle velocity through the nozzles. Typically the phosphor particles travel about four to six inches beyond the openings 45 before contacting the glass tube wall. The powder supply nozzles and the electrode member 14 are moved vertically downward at a rate determined by the desired thickness of deposition upon the interior surface of the glass wall, e.g., at about 5 inches per second for coating the T-12 or approximately 1.5 inch diameter tube ~hown in the FIG. 2 embodiment. Alternatively, the glass tube could be moved while the powder supply tubes and the electrode are kept fixed. If it is desired to deposit a second layer of pho~phor coating onto the interior surface of the lamp glass, a 6econd step of electrostatic deposition may be employed by moving the nozzels and electrode 10 bacX to their beginning positions and repeating the procedure de8cribed above. If a different phosphor is to be used for the ~econd deposition, the appropriate supply hopper would be connected to tube~ 25, 27 prior to insertion of the tubes 25, 27 into the lamp tube.
Following electro~tatic deposition of phosphors the coated bulb is cooled in air. Whether one layer or two or ~ore layer~ have been depo~ited, the phoephor coating i~ humidified by blowing satuxated air into the interior of the tube 80 that moisture is picked up on the surface~ of the particulate phosphor material.

Following humidification the lamp is lehxed to reMove the water introduced into the lamp by humidification and to bond the phosphor particles to the gla~s ~urface and to other particles in the phosphor coatings, so that the phosph~r layers will be securely bonded to the lamp interior surface after manufacture.
During phosphor deposition the glass tube is maintained at a temperature r~nge from about 150C to about 500C at which it i5 electrically conductive, la so that a current flow of approximately 2.5 milliamperes flows through the rod 12 and from the tips 16 and 18 through the glass of the lamp tube and the phosphor particles in the interior of the glas~ to the respective tips 44 of the nozzles 34. The powder being blown through the respective supply tubes into the glass bulb picks up a negative charge as it passes the corona point. The current flowing through the glass wall causes the glass to accumulate a positive charge.
As shown greatly enlarged in FIG. 5, the glass wall 20 accumulates a positive charge, shown at 80, and the phosphor particles 82 exhibit a negative charge.
Because the glass tube is isolated from the electrical system and from electrical ground, the positive charge is retained, and therefore the particulate phosphor is caused to adhere to the glass sur~ace. This retained charge will dissipate over time, but if properly isolated will retain adequate charge or a period of approximately 12 hours, 80 that the particulate phosphor can be bonded to the gla~s surface while it is still being held in place by the electrical attraction. The charge on the powder in the coating is retained because of the low conductivity of the powder. This allows sufficient time for the humidification and lehring of the coated lamp. A6 shown grea~ly enlarged in FIG. 6, a second layer 83 of ~ LD 9325 phosphor particles 84 of substantially different size than the particles 82 is deposited over the first layer 31. Humidification c~uses the layers 81, 83 of phosphor particles to be densified due to the fact that moisture on the surfaces of the individual particles causes the phosphor particles to shift slightly relati~e to each other to reduce spaces between particles and become more closely packed to the surface of the glass by the mutual attraction of the electrostatic charge. This improves the uniforrnity of the phosphor coatings on the lamp glass. The particulate layers will be maintained generally separate along a line shown at 86 at a position generally corresponding to the thickness of the first particulate layer 81 from the surface of the glass wall. Upon lehring the particles of phosphor are bound together to the glass surface to form uniform, bonded layers as shown in FIG. 6.
A lower lehring temperature may be employed following the electrostatic depoæition according to the present invention than is employed in prior art slurry deposition, because no organic binder containing carbon materials is used to initially bond the phosphor coatings to the glass. The lower lehring temperature, 475C to 600C, which would be inadequate to burn out organic binder materials, i8 adequate to cause phosphor bonding and removal of water but is not high enough to cause softening of the glass. Therefore, the sag which i~ experienced at high temperature lehring is avoided for U-shaped lamps rnade according to the present inVelltiOII, 80 that no di~tortion of lamp shape is caused by the lehring ~tep. An additional advantage of the pxesent invention i8 that only a limited amount of moisture is used in the humidifying of the lamps, thereby reducing the quantity of water which must be removed by lehring, so that the time required for lehring iB less than that required by prior art techniques even though the lehring temperature i6 lower.
The electrostatic deposition process of the present invention is not adversely affected by the pre~ence of a ~tarting strip on the interior surface of the glass tube. For example, on lamps with the tin oxide starting stripe described above deposited on the interior of the U-shaped glass tube, the present invention performs phosphor deposition with no reduction of adherence of the phosphor to the starting stripe or insulating barrier layer. Further, the present invention facilitates deposition of phosphor mixtures which may include several particle sizes, because no gravitational separation would occur and the electrostatic bonding of phosphor particles to the glass surface would not be affected by particle size~
Phosphors which are difficult to keep in suspension or are incompatible with an organic binder are readily applied by the electrostatic deposition process of the present invention because of the elimination of the binder.
It will be appreciated by those skilled in the art that the pre~ent system of electrostatic deposition of phosphors for fluorescent lamps eliminates the need for organic binders in phosphor deposition with the resultant savings of material and energy consumption while fluorescent lamp production can be completed in less time.

Claims (28)

1. An apparatus for applying phosphor coatings to U-shaped fluorescent lamp tubes while said lamp tubes are disposed in suitable holding means comprising:
power supply means for supplying a high voltage d-c potential;
electrode means connected to said power supply means for applying a high voltage d-c potential in close proximity to a U shaped fluorescent lamp tube;
particulate material supply means for supplying a continuous flow of particulate material;
particulate material deposition means connected to said particulate material supply means for providing said particulate material into the interior of said lamp tube and for applying an electrical charge to said particulate material and dispersing said particulate material into said interior of said lamp tube; and means for moving said electrode means and said particulate material deposition means relative to said lamp tube.

2. The invention of claim 1 wherein said particulate material deposition means comprises:
first and second hollow, conductive feed tube means disposed generally parallel to each other for receiving said continuous flow of said particulate material and supplying, respectively, first and second continuous streams of said particulate material to the interior of the respective legs of said lamp tube; and first and second nozzle means connected, respectively, to said first and second feed tube means for passing said first and second continuous streams, respectively, through respective first and second corona regions as said particles pass out of said respective nozzle means to cause the particles of said first and second continuous streams to become electrically charged with a first polarity.

3. The invention of claim 2 wherein:
each of said feed tube means comprises a hollow, electrically conductive tube means connected to electrical ground.

4. The invention of claim 3 wherein each of said first and second nozzle means comprises:
a hollow generally circular cylindrical body open at one end thereof and having at the opposite and thereof an end wall having a conductive tip projecting therefrom and a plurality of passages therethrough for directing the flow of particulate material over said conductive tip.

5. The invention of claim 4 wherein said electrode means comprises:
a conductive rod disposed generally between and parallel to said first and second feed tube means; and a conductive tip member attached to said conductive rod and disposed generally between said first and second feed tube means.

6. The invention of claim 5 wherein said conductive tip member comprises:
a elongated conductive member being tapered to a point at each respective end thereof attached to said conductive rod and disposed perpendicular thereto and extending generally parallel to a plane including the centerlines of both of said first and second nozzle means.

7. The invention of claim 6 wherein:
said passage pass through said end wall at a predetermined angle relative to the center line of said body such that particles of said stream of particulate material are directed toward a corona point upon emerging from said passages; and said conductive tip comprises a conical projection from said end wall having an angle of taper approximately equal to said predetermined angle.

8. The invention of claim 7 wherein:
said nozzle means and said feed tube means are constructed of stainless steel.

9. The invention of claim 5 wherein said conductive tip member comprises:
a straight conductive member attached to said conductive rod and disposed generally in axial alignment therewith so that the tip thereof is disposed between the tips of said nozzle means.

10. The invention of claim 5 wherein said conductive tip member comprises:
a straight conductive member attached to said conductive rod and disposed generally perpendicular thereto and generally perpendicular to a plane which includes the centerlines of both of said nozzles means.

11. The invention of claim 7 wherein said power supply means comprises:
a controllable d-c power supply means for providing a d-c output in the range of 20,000 to 50,000 volts.

12. A method of depositing a phosphor coating on the interior surface of U-shaped fluorescent lamp tubes comprising the steps of:
supplying particulate phosphor material to the interior of a fluorescent lamp tube via a pair of phosphor supply tubes disposed inside a U-shaped glass lamp tube;
applying an electrical charge of a first predetermined polarity to particles of said particulate phosphor material as said particles exit each respective one of said phosphor supply tubes;

applying an electrical charge of a second predetermined polarity opposite said first polarity to said lamp tube; and moving said phosphor supply tubes relative to said lamp tube so that a generally uniform coating of said particulate phosphor material is deposited over the inner surface of said fluorescent lamp tube.

13. The invention of claim 12 wherein said steps of applying electrical charges to said particles and lamp tube comprise:
applying a high voltage d-c electrical potential to an electrode member disposed in close proximity to the exterior surface of said fluorescent lamp tube;
connecting each of said phosphor supply tubes to electrical ground; and moving said electrode member relative to said lamp tube simultaneously with moving said phosphor supply tubes.

14. The invention of claim 13 further comprising:
humidifying the interior of said fluorescent lamp tube; and lehring said fluorescent lamp at a predetermined temperature for a predetermined time to remove moisture from the interior of said fluorescent lamp tube and to bond said particulate phosphor material to said fluorescent lamp tube.

15. The invention of claim 14 wherein said step of applying a high voltage d-c potential comprises:
supplying a d-c voltage in the range of 20,000 to 50,000 volts to said electrode member.

16. The invention of claim 15 wherein:
said step of applying an electrical charge to said particles comprises applying a negative charge to said particles; and said step of applying an electrical charge to said lamp tube comprises applying a positive charge to said lamp tube.

17. The invention of claim 16 wherein said step of moving said phosphor supply tubes relative to said lamp tube comprises:
moving said phosphor supply tubes at a predetermined rate.

18. The invention of claim 17 wherein said predetermined rate comprises:
a rate of about 5.0 inches per second.

19. The invention of claim 13 further comprising:
prior to said step of supplying particulate phosphor material; positioning first and second nozzle tips attached to respective ones of said phosphor supply tubes at a predetermined position within the parallel legs of said lamp tube relative to the bight of said U-shaped glass lamp tube; and positioning said electrode member at a position between the edge of said bight of said glass lamp tube and a plane through the ends of said nozzle tips,

20. The invention of claim 19 wherein:
said step of applying said high voltage d-c electrical potential comprises producing a corona surrounding each of said respective nozzle tips during said step of moving said electrode member and said phosphor supply tubes.

21. The invention of claim 20 wherein:
said steps of moving said electrode member and said phosphor supply tubes comprises moving said electrode member and said phosphor supply tubes the entire length of the legs of said U-shaped glass lamp tube.

22. A method of depositing phosphor materials on the interior surface of U-shaped fluorescent lamp tubes comprising the steps of:

supplying a first particulate phosphor material to the interior of said fluorescent lamp tube via a pair of electrically grounded phosphor supply tubes;
applying a high voltage d-c electrical potential to an electrode member disposed in close proximity to the exterior surface of said fluorescent lamp tube;
moving said electrode member and said phosphor supply tubes relative to said fluorescent lamp tube so that a first generally uniform coating of said first particulate phosphor material is deposited over the inner surface of said fluorescent lamp tube;
supplying a second particulate phosphor material to the interior of said fluorescent lamp tube via said pair of phosphor supply tubes;
applying a second time a high voltage d-c electrical potential to said electrode member disposed in close proximity to the exterior surface of said fluorescent lamp tube; and moving said electrode and said phosphor supply tubes relative to said fluorescent lamp tube so that a second generally uniform coating of said second particulate phosphor material is deposited over said first coating of said first particulate phosphor material.

23. The method of claim 22 further comprising:
after said first and second coatings are deposited humidifying the interior of said fluorescent lamp tube: and lehring said fluorescent lamp tube at a predetermined lehring temperature for a predetermined time to remove moisture from the interior of said fluorescent lamp tube and to bond said particulate phosphor materials to said fluorescent lamp tubes

24. The invention of claim 23 wherein:
said predetermined lehring temperature is in the range of 475 degrees centigrade to 600 degrees centigrade.

25. The invention of claim 23 wherein said step of humidifying comprises:
supplying saturated air to the interior of said fluorescent lamp tube.

26. The invention of claim 22 wherein each step of applying a high voltage d-c potential comprises:
supplying a d-c voltage in the range of 20,000 to 50,000 volts to said eletrode member.

27. The invention of claim 22 further comprising:
prior to said step of supplying said first particulate phosphor material; heating said fluorescent lamp glass tube to a predetermined temperature sufficient to cause the glass tube to become conductive.

28. The invention of claim 27 wherein said predetermined temperature is in the range of 150 degrees centigrade to 500 degrees centigrade.