US2830214A - Electronic fluorescent illuminating lamp - Google Patents

Description

' Ap 1958 ROGER FRANCOIS DESIRE NAVARRE 2,330,214

; ALIAS MALHERBE ELECTRONIC FLUORESCENT ILLUMINATING LAMP Filed Jan. 3, 1955 2 Sheets-Sheet 1 ATTORNEYS p 1958 ROGER FRANCOIS DESIRE NAVARRE 2,830,214 ALIAS MALHERBE ELECTRONIC FLUORESCENT ILLUMINATING LAMP 2 Sheets-Sheet 2 Filed Jan. 5, 1955 m7 '4 V l/IIIIIIIIIIl/l/l INVE/V TOR ROGER FRANQO/S DES/RE NAVARREAUAS MALHERB/E 2,830,214 ELncrnoNrc FLUORESCENT ILLUMINATING LAMP Roger Frangois Dsir Navarre, alias Malherbe, Paris, France, assignor, by mesne assignments, to Sebel S. An, Tangier, Morocco Application January 3, 1955, Serial No. 479,604

Claims priority, application France January 16, 1954 4 Claims. (Cl. 313-109) anode, while a fluorescent coat is provided in the path of the electrons emitted by the cathode, so that the kinetic energy acquired by said electrons under the action of the dilference in potential applied between the anode and the cathode shall be transformed into luminous energy at the moment of the impact of the electrons on the fluorescent coat.

As disclosed in the above mentioned patent application, I have found, when executing such an illuminating lamp, that the spacing of the anode with reference to the cathode requires, if it is desired to obtain a substantial luminous intensity without employing prohibitive voltages, the use of means capable of neutralizing partly the space charge.

The principal means proposed for this purpose in the said patent application Serial No. 349,436 consist in inserting between the cathode and the anode two grids one of which is brought to the potential of the cathode or to a potential that is slightly negative with reference to the latter, while the other grid is brought to a potential that is positive with reference to the cathode, the two grids having substantially the same pitch and the bars or elements of the positive grid being located in the electronic shadow of the grid which has a zero or negative voltage with reference to the cathode.

The use of such a system of aligned grids applied thus for the first time to fluorescent electronic illuminating lamps of the type described in the above mentioned patent application, was already known per se in the execution of electronic tubes as used for usual electronic application purposes.

It has however been ascertained in accordance with the present invention that the execution of such a system requires solving a very particular problem in the case of illuminating lamps, particularly due to the fact that, owing to the particular shape which must be given to the anode so as to provide for the desired efliciency of the emitted luminous flux, the anode-cathode distance is not uniform.

The present invention has more particularly for its object arrangements permitting to obtain a practically uniform distribution of the electrons over the entire surface of the anode in spite of the particular shape of the latter.

Said arrangements will be better understood from the following description, reference being made to the appended drawings given by way of non-limitative examples, and in which:

Fig. 1 is an axial vertical cross-section of an electronic fluorescent illuminating lamp of the type described in the said patent application No. 349,436;

Fig. 2 is a similar view of a modification of the lamp of application Serial No. 349,436;

United States Patent Fig. 3 is a diagram explaining the phenomena on which is based the present invention.

In the example illustrated in Fig. l, the chamber 1 of the lamp is defined by a bulbof glass or the like transparent material, the shape of which is similar to that of a mushroom and the socket of which is provided with a fitting that is not illustrated and by which it may be mounted after the manner of the conventional'incandescent bulbs. 2 designates an electron emitting cathode of the indirectly heated type constituted for instance by a nickel tube of any suitable cross-section, that is coated with emissive substances and is arranged substantially along the axis of the bulb 1. The heating of said cathode is provided for by a helically wound filament 9 of tungsten covered with alumina or the like insulating material and extending inside the cathode tube 2. The cathode 2 and the filament 9 are fitted in the two superposed mica washers 10 and 11 carried at the corresponding ends of the cathode by the socket in; said washers serve also as supports for the two grids 12 and 13 surrounding the cathode 2 and which will be described with further detail hereinafter.

The inner wall of the portion of the bulb 1 nearest the socket is covered by a metal layer 14 forming the anode and over which is applied a fluorescent coat 6. The wall of the part of the bulb that is opposed to the socket is, in the example illustrated, devoid of any coat and forms a transparent gate which provides a free passage for the luminous rays emitted by the coat 6 in the direction that is best suited for the utilization of the lamp.

The grids 12 and 13 are constituted for instance by helices of circular or rectangular cross-section that are secured to the mica washers 10 and 11 by the longitudinal bars 15. The inner grid 12, located in the immediate proximity of the cathode 2 is, in the present case, electrically connected with the latter. It may also be brought by any suitable means to a negative voltage with reference to the cathode. The outer grid 13 is connected electrically with the anode 14 or brought in any suitable manner to a positive potential with reference to the cathode. As already mentioned hereinabove, the convolutions of grid 13 are arranged with reference to those of the grid 12 in a manner such as to lie in their electronic shadow.

In the modification illustrated in Fig. 2, the anode 14 and the fluorescent coat 6 are applied as in the'example of'Fig. 1 to the portion of the inner wall of the bulb 1 adjacent to the socket 1a, out the cathode 2 and the grids 12 and 13' are constituted by flat elements extending perpendicularly to the axis of the bulb 1, the heating filament 9 being positioned in parallelism with the plane of the latter. By reason of this arrangement, the infrared rays emitted by the cathode 2 are directed for the major part towards that part of the wall of the bulb that is not coated with a fluorescent substance and they exert consequently no light-extinguishing effect-on the coat 6.

Now, it is a well known fact that in an electronic device having aligned grids successively spaced from the cathode, the electron beams starting from the cathode and passing respectively through the different successive grids are divergent and consequently cross one another so as to produce an area with a high electron density. This phenomenon is illustrated diagrammatically in the upper part of Fig. 3 in association with a chart in the lower part of Fig. 3 illustrating the spacial distribution of the potentials, inside an electronic tube having successively positioned aligned grids, as a function of the location of the anode. In this representation of Fig. 3, K designates the cathode, and G1 and G2 designate the two aligned cylindrical grids of the embodiment of Fig. l surrounding the cathode, while A is the anode. In the chart in the lower part of Fig. 3, the distances between the anode and the cathode are marked as abscissae while the voltages are marked as ordinates. For sake of clarity, the voltage Va of the anode has been assumed to be higher than the v taseVsZ el -the r d G2. but obviously other v u of the anodic voltage are also suitable.

Turning to Fig. 3, it is apparent that the above mentioned phenomenon of high electron density due to beam crossover disturbs by no means the spacial distribution of the voltages between the grids G1 and G2 and the anode A for distances between anode and cathode such as those shown as Dc and DI where there is no beam crossover. In contradistinction, when the anode is lo cated at distances from the cathode such as D2, D3, D4, etc., beyond distance Dc the space charge produced by the high electron density at the points where the electron beams cross one another disturbs to a substantial extent the normal spacial distribution of the voltages between G2 and A.

The distance Dc at which the electronic paths cross one another is termed the critical distance. Said distance depends, on one hand, on the geometrical structure of the electrodes and, on the other hand, on the voltages applied to the latter. in Fig. 3, the locus of points at the critical distance is shown as a straight line, but it may be a curve, depending on conditions.

When the aligned grid systems are used in electronic tubes of the type used for usual electronic application purposes wherein the anode-cathode distance is uniform, it is of advantage to produce a space charge between the outer grid G2 and the anode so as to cut out any disturbance due to an auxiliary emission of electrons. It is then unnecessary to provide a suppressor grid. 7

It is thus apparent that in the case of tubes used for usual electronics application purposes, it is of advantage for the anode to be always positioned with reference to the cathode beyond the critical distance Dc. The action of the space charge thus produced on the secondary electrons which have a very reduced energy is considerable, and the action of the space charge is on the contrary negligible on the primary electrons, except for very low anode voltages.

In the case of the fluorescent electronic illuminating lamp forming the object of my said patent application Serial No. 349,436 (see in particular Figs. 1 and 2 of the annexed drawings of this present application), the anodecathode distance is not uniform, by reason of the shape to be given to the anode 14 so as to provide for the desired efiiciency of the luminous flux. If it is desired to obtain a uniform distribution of the beams of electrons over the entire surface of the anode 14, it is necessary for the locus of the points lying at the critical distance to be very near the anode and to match the shape of the latter. This result may be achieved according to the present invention by giving a suitable shape to the cathode and to the aligned grids and possibly by incorporating further electrodes of suitable shape and at suitable voltages between the second or outer grid and the anode.

A simpler arrangement which forms also part of the present invention consists in positioning the point of the anode which is farthest from the'second or outer grid, within the critical distance. Thus there is no space charge between the second grid and the anode.

In the case where the system comprising the cathode and the two aligned grids does not lead to the production of a critical distance which is large enough to allow satisfying the above-defined condition of locating the fartherest point of the anode, it is possible to associate advantageously with said system additional electrodes having suitable shapes and maintained at suitable voltages so as to increase sufficiently said critical distance.

What I claim is:

1. An electronic fluorescent illuminating lamp comprising a transparent evacuated bulb, an electron-emitting cathode and an anode inside said bulb, means for producing a flux of electrons between the cathode and the anode, and a coat of fluorescent material carried inside the bulb in the path of the electron flux and adapted to transform the kinetic energy of the electrons flowing between the cathode and the anode and impinging on said coat into luminous energy, and two successively spaced grids screening the cathode with reference to the anode, means for biasing the first grid that is nearest to the cathode to a potential that is at the utmost equal to that of the cathode, and means for biasing the second grid more remote from the cathode to a positive potential with reference to the cathode, the two grids having substantially the same pitch and the elementary parts of the second positively biased grid being located in the electronic shadow of the other grid, and the cathode and the two grids being soshaped and positioned that the locus of the points located at the critical distance of crossover of the two beams of electrons from the cathode passing respectively through the said two grids is very near the anode and corresponds substantially in shape to the latter.

2. An electronic fluorescent illuminating lamp comprising a transparent evacuated bulb, an electron-emitting cathode and an anode inside said bulb, means for producing a flux of electrons between the cathode and the anode, and a coat of fluorescent material carried inside the bulb in the path of the electron flux and adapted to transform the kinetic energy of the electrons flowing between the cathode and the anode and impinging on said coat into luminous energy, and two successively spaced grids screening the cathode with reference to the anode, means for biasing the first grid that is nearest to the cathode to a potential that is at the utmost equal to that of the cathode, and means for biasing the second grid 7 more remote from the cathode to a positive potential with reference to the cathode, the two grids having substantially the same pitch and the elementary parts of the second positively biased grid being located in the electronic shadow of the other grid, and the cathode and the two grids and the anode being so shaped and positioned that the point of the anode which is the farthest from the second grid is located nearer the cathode than the locus of points at the critical distance from the cathode of the crossover of the two beams of electrons from the cathode passing respectively through the said two grids.

3. An electronic fluorescent illuminating lamp according to claim 1, in which auxiliary electrodes suitably shaped and biased to bring the locus of the points located at the critical distance nearer to the anode are inserted between the said second grid and the anode.

4. An electronic fluorescent illuminating lamp accordingto claim 2, in which auxiliary electrodes value are inserted between the said second grid and the anode and areso shaped and positioned and biased as to remove the locus of points at said critical distance to be more remote from the cathode than the point of the anode which is farthest from the second grid.

References Cited in the file of this patent UNITED STATES PATENTS

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