US2621284A

US2621284A - Direct current arc having reflector means superimposing a reverse complementary image on the arc

Info

Publication number: US2621284A
Application number: US760920A
Authority: US
Inventors: Gretener Edgar
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-07-13
Filing date: 1947-07-14
Publication date: 1952-12-09
Anticipated expiration: 1969-12-09

Description

Dec. 9, 1952 E GRETENER 2,621,284

DIRECT CURRENT ARC HAVING REFLECTOR MEANS SUPERIMPOSING A REVERSE COMPLEMENTARY IMAGE ON THE ARC Filed July 14, 1947 I 1 lC/mm INVENTOR EDGAR GRETENER BY M J V20 WAGE ANGLE OF VIEW ATTORNEYS ARC Patented Dec. 9, 1952 DIRECT CURRENT ARC HAVING REFLECTOR MEANS SUPERIMPOSING A REVERSE COM- PLEMENTARY IMAGE ON THE ARC Edgar Gretener, Zurich, Switzerland Application July 14, 1947, Serial No. 760,920 In Switzerland July 13, 1946 8 Claims.

(Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G. 5)

The present invention is concerned with increasing and improving the illumination obtainable from an arc source.

It is an object of the invention to compensate for the dark area normally surrounding the negative electrode of a carbon arc.

It is an object of the invention to distribute the incandescent gases constituting a carbon arc in such a manner that the light produced is maximized.

It is an object of the invention to superimpose upon an arc lamp reflector a reverse complementary image of the are so that the light level of the negative dark area is brought up to that of the rest of the arc.

It is an object of the invention to make a carbon are light source having a brilliant positive crater, a dark negative electrode area and a resultant irregular light distribution or gradient between electrodes into a light ource which is maximum in both brilliance and homogeneity by first moving some of the glowing ionized vapors forming the are away from the brilliant positive arc crater toward the dark negative electrode in such a manner that although the negative electrode area is still darker than the positive electrode area, the gradient or rate of change of light intensity or value between electrodes is often nonuniform but is usually and in the same direction, that is, constantly decreasing from the positive electrode to the negative electrode. When such an arc with a variable gradient of light level is combined with its reversed substantially complementary image not only is the light level throughout the arc the same, i. e., substantially zero gradient, but the light level is maximized because all practically available light is utilized.

Other objects will appear as the description continues. The following disclosed structure is intended to be illustrative of a few of the forms the invention may take and is not to be considered as limiting. In the drawing like numbers refer to like parts throughout.

In the drawings:

Fig. l is a schematic elevation of a carbon arc with means to distribute the arc.

Fig. 2 is a schematic sectional View of means for superimposing a complementary arc image.

Fig. 3 is a schematic sectional View of a second arrangement similar to Fig. 2 but with a main reflector having a smaller radius of curvature, for increasing the apparent homogeneity of the arc.

Fig. 4 is a schematic sectional View of a third arrangement for increasing the apparent homogeneity of the arc.

Fig. 5 is a graph of the illumination level measured along the arc column of Fig. 3.

Positive carbon I0 and negative carbon I I have an arc I2 of incandescent carbon gas there between maintained by current flow. The bright spot'of the normal carbon arc is the crater I3 in the end of the positive carbon I0, the area around the end of negative carbon II being relatively dark. A first step in improving the are as a light source is to move some of the hot gases from around crater I3 to the area around negative corbon II. This may be accomplished by a nozzle I4 around positive carbon I0. Nozzle I4 may be made of metal or ceramic material as desired and mounted on the carbon holder together with the carbon feeder usual in carbon arc lamps. Nozzle I4 is shown in outline only and is connected to a supply line I5 through which a gas such as air is forced under pressure. If desired a gas such as nitrogen or carbon dioxide may be used to decrease the oxidation of carbons I0 and I I. Where the atmosphere of the arc itself is drawn off and recycled a higher arc efliciency is maintained. The gas is nozzled to obtain sufficient velocity and caused to flow through annular orifice I6 surrounding positive carbon II]. As shown in Fig. 1 the arc I2 is smoothed into a cylindrical column by the flow of the nozzled gas and concentrated between the electrodes I0 and I I. Parts of the arc I2 are caused to surround negative carbon II as at IT. This distribution of the incandescent gas of the arc gives a more uniform cylindrical light source.

While the above redistribution of the arc I2 aids in forming a satisfactory light source, the arc portion I! is still relatively dark.

This is the first step. The pressure and volume of the air flow around arc I2 is so chosen that the distribution of the incandescent ionized gas yields a more uniform light source cylinder and in so far as is possible one in which the respective halves or selected portions are reasonably complementary. That is, although the light level along the arc is not uniform the critical peak at the crater has been ironed out and the dark area around the negative electrode filled in so that the blown arc plus its reversed complementary image yields a composite light source of uniform intensity along its length. This is true because if to each instantaneous value of light intensity along the arc is added its adjusted complementary value the result will be a constant value of light intensity along the arc. This of course assumes that the pressure and air volume are adjusted so that the arc portions are in fact complementary or reasonably so over a desired distance.

In carbon arc illumination system it is customary to use a reflector such as a concave mirror I8. The axis of the arc stream I2 can be placed in line with, or perpendicular to, the optical axis of concave mirror I8. The mirror I8 can reflect only a part of the light from are I2 and although there is direct emanation that portion of the light not utilized by main reflector I8 is not efficiently directed. It has been found that by placing an auxiliary mirror or reflector iii so as to embrace the solid angle not included by the main reflector 58, a reversed image of the light source is superimposed on itself. Main reflector 18 now reflects both the light falling directly upon it from arc l2 and that reflected upon it by auxiliary reflector 19. Thus the arc l2, as seen from the main reflector I8, is a light cylinder with an approximately homogeneous brightness. The lumen output per unit of apparent arc cylinder area is a substantial constant within reasonable limits. With this arrangement, it appears to main reflector l8 as if are 12 were burning between two positive carbons. By superimposing the image on to the actual arcv to give a homogeneous brightness distribution along the arc cylinder axis, the average apparent brightness of the arc stream [2 is considerably increased. More usable light is obtained.

In general, the solid angle of the auxiliary mirror symmetrically placed about the mid-point of the light cylinder is made equal to the solid angle of the main reflector. The illumination system of the combined auxiliary mirror and main reflector gives. its maximum li ht o"=tp t when the total angle of embrace of both reflectors with respect to arc i2 is 360 degrees. Such an arrang ment for the case of a parabolic :main reflector i8 is shown in Fig. 2 in which main reflector l8 subtends 180 degrees or one pi radians of the angle about the axis of carbon electrode i2 and auxiliary reflector I9 also subtends 180 degrees or one piradians, making 360 degrees in all.

The auxiliary mirror may be used in a number of ways. For example, in Fig. 3 the axis 20 of arc stream I2 is perpendicular to optical axis 21 of main reflector 22. In Fig. 4 axes 20 and 2! coincide. The are I2 is superimposed on itself by auxiliary mirror l9 when the center of curvature 23 coincides with the mid-point between the ends of carbons Hi and II, which are then imaged at 24 and 25 respectively. From the view point of the main reflector or mirror 22 a practically constant arc brightness appears between the crater 13 in positive carbon [0 and its image 24. Be.- yond these limits the level of illumination rapidly decreases.

As shown in Fig. 3 where great homogeneity of light'level is desired the focus 23 is displaced from the midpoint between electrodes toward the positive crater [3. This brings the reversed image 24 of crater l3 closer and makes a shorter effective combined arc image with some loss of light, but with a gain in homogeneity required by high fidelity reproduction with a photo electric cell.

It has been found that auxiliary mirror l9 becomes very hot when placed in close proximity to the are 12 as the radiant energy it receives, While no more than that received by the main reflector 22, is concentrated in a relatively small mass with a limited radiating surface. This is true even though mirror i9 is an excellent reflector. While ceramic reflectors may be used a metal mirror is preferred. First, the metal itself can be polished to reflect. Where a plated reflecting coating is used the bond between the reflecting coat and the supporting metal is usually so good that they act as a single piece of metal. This is seldom true of metal coatings on ceramic mountings where high temperatures are involved. Second, metal reflectors are much more readily cooled. The rapid conduction of heat to all parts permits direct water cooling for highest efficiency. In general, however, forced air cooling is suiflcient. The

back of a metal mirror acts as a suitable radiator of the absorbed heat. It may be finned as at 26 if desired, care being exercised that the fins 26 do not intercept the light.

Fig. 5 shows the illumination level with respect to position along the arc column of an arrangement such as shown in Fig. 3. In the graph the abscissa represents distance along the arc between the electrodes shown and the ordinates corresponding values of light level or brilliancy as determined by a sensitive light meter. The line of observation during the measurements was inclined by an angle of approximately sixty degrees to the axis of the arc column as indicated by arrow ml. The curve )2 shows the brightness of the are column without an homogenizing mirror 22. Curve I93 shows the increase in brilliancy obtained by superimposing the inverse arc image on curve H32 and adding the two ordinates. Curve Hi l shows the brilliancy of the arc image taken alone. Due to parallax resulting from the angle of observation the maximum brilliancy or peak of curve I82 will be seen to appear displaced somewhat to the right away from the edge of the crater. The brilliancy of the crater adds to the brilliancy of the arc column because of the search light eifect of the incandescent hollow crater with its polar axis coinciding with the longitudinal axis of the arc column. The maximum brlnizancy of the reversed image is somewhat lower than the arc column maximum due to the absorption losses within the ionized gaseous column and to the deviation from unity of the in.- dex of reflection of the reversing mirror. Curve Hi2 shows that the brilliancy of the homogenized arc column is practically or substantially uniform up to a certain point which corresponds tothe location of the image of the separation edge between the arc column andthe positive crater. Beyond that critical point, as shown by graph I03, 17119 lrluflllllafilfill ISV'SJ. O1 brnnancy lfipluiy cecreases.

It will be noted that the invention achieves its result as a practical matter. That is to say for practical purposes graphs Hi2 and I04 are complementary in suiflcient degree to combine to produce a substantially or practically uniform portion in curve I03. Mathematical exactness in the sense of a curve portion parallel to the abscissa is not required, but of course the result improves as it is approached.

While I have described my invention in terms of physical structure, it will be readily understood that structure other than that described may embody the spirit of the invention.v The claims are presented to set forth the invention in more general terms and the foregoing description is offered as an aid in their interpretation and is not to be taken to limit their scope. The detailed structures disclosed above are oifered as specific examples or species of the generic terms appearing in the claims.

An example of the above is the use of a magnetic focusing coil 27 to compress the hot ion cloud around crater l3 and move the incandescent gas toward negative electrode H. Again electrostatic fields may be applied to the arc stream l2 to accelerate ions in their flow and cause the stream 12 to take a more uniform cylindrical shape.

It will be appreciated with the use of coincident axes 20, 2| as shown in Fig. 4-. a blown are or its magnetic equivalent obtained with a coil 21 is necessary. A polar diagram of illumination from the common positive crater indicates no light from the brilliant crater passes the plane normal to the electrode at the crater end. The threedimensional light level diagram of the crater forms an oblate spheroid tangent to the crater l3.

This spheroid is directed away from reflector 22. On the other hand a blown arc produces an intensity diagram in the form of a torus surrounding the arc cylinder and having a substantial portion directed toward reflector 22 positioned a in Fig. 4.

I claim:

1. In combination in a direct current are lamp assembly, a positive carbon electrode having a brilliant crater, a negative electrode, means to move portions of the ionized gas forming the arc away from said crater and toward said negative electrode to form a corrected arc column having a light distribution over an effective portion of the distance between said electrodes of such value that for each point of said effective portion the sum of the light value of a given point of said portion plus the light value superimposed by a corresponding point of the reversed image of said portion is substantially a constant for all such pairs of points when superimposed in additive relation, a main reflector for said light producing corrected arc column having a, focal point adjacent said column, a spherical auxiliary reflector embracing a large solid angle of the order of pi radians and having a focal point positioned to reflect a reversed image of said corrected arc column upon said column, said main reflector serving to project a beam of brilliant homogeneous light combining the beams from said corrected column and said reversed image, whereby a carbon are having an irregular light gradient is given a light gradient of such character over an effective portion of the distance between electrodes so that when combined with its complementary reversed image the combination produces a beam of light having substantially the same level of intensity along a length corresponding to said portion suitable to be condensed to produce an intense homogenous image of its source comprising the corrected portion of the arc column and its reversed image in complementary relation.

2. The combination set forth in claim 1, said means to move portions of the ionized gas forming the arc comprising nozzle means surrounding said positive electrode to direct an annular stream of gas around and along said positive electrode and the are between said electrodes to form a short, smooth, brilliant arc-light source cylinder between said electrodes.

3. The combination set forth in claim 2, having means to cool said auxiliary reflector to retain its accuracy as an optical surface.

4. The combination set forth in claim 3, said means to cool said auxiliary reflector comprising fins on the side thereof removed from said arc and serving both to increase the radiating capacity of the said auxiliary reflector and the structural strength thereof to minimize warping.

5. The combination set forth in claim 1, the optical axis of said reflectors being normal to the axis of said electrodes.

6. The combination set forth in claim 1, the optical axis of said reflectors being coincident with the axis of said electrodes.

7. In combination in a direct current arc lamp assembly, a positive carbon electrode having a brilliant crater, a negative electrode, means to move portions of the ionized gas forming the are away from said crater and toward said negative electrode to form a corrected arc column having a light level distribution along an effective portion such that when added to the reversed image of said portion the composite source has a substantialy uniform light level, a main reflector for said light producing corrected arc column having a focal point closely adjacent said portion, a spherical auxiliary mirror embracing a solid angle of the order of pi radians having a focal point also closely adjacent said portion and positioned to reflect a reversed image of said corrected arc column upon said column adjacent the said focal point of said main reflector, said main reflector serving to project a beam of brilliant homogeneous light combining the beams from said corrected column and said reversed image, whereby a carbon are having an irregular light gradient is given a substantially uniform light gradient between electrodes and combined with its reversed image to produce a beam of light having substantially the same level of light in tensity throughout and suitable to be condensed to produce an intense homogeneous image of its source ocmprising the corrected arc column and its reversed image in complementary relation.

3. In combination in a direct current are assembly, a positive carbon electrode having a brilliant crater, a negtaive electrode, said electrodes being constructed and arranged to form an arc therebetween, a main reflector for said arc, a spherical auxiliary reflector embracing a large solid angle of substantially one pi radians having a focal point positioned to reflect a reversed image of said are upon said are, said main reflector serving to project a beam of brilliant homogeneous light combining the beams of said are and its reversed image, whereby a carbon are having an unequal light level distribution along an effective portion is combined with a reversed complementary image of said are to produce a uniform lighting effect.

EDGAR GRETENER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,078,913 Fleming et al Nov. 18, 1913 1,853,533 Arbuckle Apr. 12, 1932 2,003,675 Berg June 4, 1935 2,068,795 Gleick Jan. 26, 1937 2,078,639 Schneider Apr. 27, 1937 2,107,148 Gretener Feb. 1, 1938 2,204,079 Gelb June 11, 1940 FOREIGN PATENTS Number Country Date 311,704 England Feb. 13, 1930 700,077 France Dec. 22, 1930