US2144673A - Incandescent lamp and its manufacture - Google Patents

Description

Jan. 24, 1939. C B,RDSEYE ET AL I2,144,673v

INcANDEscENT LAMP AND 1Ts MANUFAGTURE Filed Ogl.. 5l, 1935 fig. Silver Cov/fing A figg. 7.

Molded Base Maer/'a/ Panarea Jan. 24, 1939 UNITED sTliTlazsV anatra INCANDESCENT LAMP AND ITS MANUFACTURE Clarence Birdseye and Pincus Deren, Gloucester, Mass., assignors to Birdseye Electric Company, Gloucester, Mass., a corporation of Delaware Application October 31, 1935, Serial No. 47,581

11 Claims.

This invention relates to the manufacture of incandescent lamps and more particularly to such lamps in which the bulb is provided with a reflecting ksurface for increasing the amount of light from such a source available for useful In the manufacture of incandescent lamps of the kind having a reflecting lamp bulb certain of the light rays from the bright filament of the l0 lamp are intensified by refiection from -a refiecting surface formed by-silvering a part of the wall of the bulb. For direct lighting the filament is hooded by the reflector, the lower limit of the silvered area being preferably-at such a distance from the filament that all of the rays emanating from thefilament, both direct and refiected,

eventually will `leave the lamp Within a predeabove, below or at one side of the filament accord-x ing to the position of the lamp when in use and the above described relation of the boundary of the reflector to the filament may be varied considerably for indirect lighting, where the area o'f the illuminated field may profitably be very greatly increased. It has been found that in by the use of a reecting bulb and in the case of direct lighting there is the further advantage of having the intensely bright spot of -the filament effectively removed from the field of vision.

In developing a commercially successful refleeting bulb for incandescent lamps several diiculties Were encountered and largely overcome but in the solution other disadvantages developed which this inventionhas eliminated.

One part of the problem was tov eliminate from the useful eld of light any projected image of the filament. Such a projection of a distorted image of the filament, thereby making a very bright area in the illuminated zone is due to the l fact that the filament is preferably located at or near what may be described as the focus of the reflecting surface of the bulb. Heretofore, the solution of this problem has been attempted by frosting the lower or useful light emitting area of the bulb below the silvered or reiiecting area, or

above it, in the case of lamps having the lower portion of the bowl silvered. This treatment will' diffuse the useful light to a certain extent and so 60 tend to eliminate the discordant bright area, but

either case the emciency of the lamp is increasedk with considerable increased loss of light, as explained below.

Another part of the problem was to eliminate any tendency of the lamp to cast a shadow of the filament near the center of the brightly illuminated field due to the reected light impinging in part on the filament itself. This shadow tends to center with the reflected image of the bright filament, but because of the irregularity and non-symmetry of the parts of the filament and because they are not located at any true focus of the reflecting area, the shadow and the bright image do not register but `there is built up a zone that is of different brilliancy than the rest of the illuminated area, most of which is brighter but with a mottling of shadow. A diffusion of the emitted light by frosting as above described has heretofore been resorted to in an attempt to solve this problem, and with similar introduction of losses.

Frosting the area of the bulb through which light is emitted has a serious disadvantage in that the high concentration of the bright rays passing through the frosted glass tends to unduly raise the temperature of the glass due to the absorptive power ofthe frosting, and this increased loss as heat represents a substantial loss of useful light.

One object of the present invention is to in` crease the eiciency of reiiecting lamps by eliminating high-lights and shadows within the useful lighting zoneall without decrease in intensity of either the direct or reflected light rays from the source of light.

In achieving this object a new method is employed of producing a diffused light from a highlamp, thus neutralizing any distinct focusing effect and producingv a substantially uniform intensity of illumination throughout the lighted area without loss of efcicncy'. The employment of this new method permits the manufacture of reecting bulb incandescent lamps with clear glass below the reflecting area thus allowing all of the light rays, in undiminished brilliancy, to illuminate the useful field.v

This invention, in its broader aspects, embraces within its field the diffusion of light through the medium of a diffusing reflector in contradistinction to the diffusion of vlight by transmitting through a diffusing body. A particular application relates to diffusing the light from reecting bulbs so as to eliminate from the illuminated field either the partially focused image or the shadow of the filament or other source of light.

In order that the later use of the term diffusing reflector may be understood the distinction between reflected light with and without diffusion should be'borne in mind. In an ordinary or plane reflector lhaving a smooth reflecting surface or mirror the angle of incidence is always equal to the angle of reflection from the particular point under consideration. When the reflecting surface is not a single plane, for example a curved surface, these angles are measured with respect to a planetangent to the surface at thepoint in question. Thus at any point on such a curved reflecting surface the light rays are still directly reflected and at all points the two angles are always equal. Such smooth reflectors provide specular reflection.

In a diffusing or non-specular reflector the angle of'reflection at any point on the surface may be any angle whatever with respect to the general contour or surface plane of the reflector. 'I'hat is, although by chance certain rays and beams may be reflected at the angle of incidence, practically all of the rays and beams falling on a diffusing reflector will be reflected at an angle different from the angle of incidence with respect to the surface plane of the reflector. A diffusing reflector will therefore have a very large number of minute or microscopic surface irregularities which individually may form almost any angle whatever with the plane of the reflector as a whole. Each of these microscopic surface irregularities acts as an individual mirror and the angles of incidence with respect to the surface plane of the reflector and reflection from each individual mirror are, of course, equal. Reflected light from such a mirror is diffused, that is it leaves the mirror in almost all possible directions.

A specific application of the invention in commerce is to incandescent lamp bulbs having a portion of the wall of the bulb prepared as a highly efficient diffusing reflector. The lamp bulb may be of the conventional shape or of almost any special shape and yet gain a pronounced beneilcial effect by having some part of its surface acting as a diflusing reflector. In any application of the invention to lamp bulbs the surface of that part of the wall of the bulb acting as the reflector may have been modified either at the time of making the bulb or by a subsequent treatment enabling diffusion of light, or modified by the kind of reflecting surface applied to create a diffusing reflector, its roughened, irregular or uneven reflecting surface being formed either before or after or during the operation that produces the reflector itself.

In the past, difficulties have been encountered in producing an efficient, durable and attractive reflecting silver film on the inner surface of an evacuated glass vessel or one to be evacuated. These diilliculties are no doubt responsible for the fact that prior to my work no satisfactory insidesilvered lamp bulb was commercially available. One difficulty was that it was found impossible to make a silver fllm ladhere evenly and uniformly to the inside surface after evacuation. The silver could be deposited by any well-known process, but when the bulb was thereafter evacuated, bubbles would make their appearance in the silver fllm which, on bursting, would permit the silverito peel off the glass wall.

It was subsequently discovered that the difficulty was due to a physical and possibly chemical change of the surface layer of the glass, after which change the layerreadily occluded gases because of its more spongy nature. The usual cleaning processes employed in the art produced little or no effect on this layer, so that upon evacuating the bulb, the occluded gases would expand and give rise to the bubbles which destroyed the continuity of the silver film.

In copending application, Serial No. 42,227, filed September 26, 1935, Pincus Deren describes the mentioned difllculties and discloses a method of eliminating this injurious gassy layer without affecting the transparency of the bulb, by a variation of the well-known etching process. It is also a part of our invention to eliminate the gassy layer prior to silvering, but, since my primary interest is in a diffusing surface and my'preferred means for obtaining it is to etch or frost the inner surface of the bulb prior to silvering, we may use any common etching or frosting solution, preferably one giving a good even and unlform frost with no marked depressions.` When,

on the other hand, we desire to deposit silver on a smooth transparent surface, we may utilize the etching solution disclosed by Deren for this purpose. In either case, the etching process serves to remove the objectionable gassy layer and prepare the inner surface of the bulb for receiving the deposited silver in such a way that after sllvering and evacuation, a fine, attractivesilver fllm is obtained having no holes, bubbles or peeled spots. By depositing the silver upon a roughened or frosted glass surface we have found that the film adheres very strongly.

A further problem arises in the case of inside frosted bulbs by reason of the fact that the inside frosting process seriously weakens the glass, presumably by the formation of myriads of minute crevices at the bottom of which the thickness of the glass is below the safe limit. In the past it has been necessary to give to inside frosted bulbs a second etching and strengthening treatment which necessarily adds to the cost of production. Such a strengthening treatment, now widely employed in the manufacture of insidefrosted non-reflecting bulbs, is disclosed in U. S. Letters Patent No. 1,687,510, to Pipkin.

We have found that such second strengthening treatment is. wholly unnecessary in the case of my inside frosted, silvered bulbs, because the silver film coats the sharp crevices and strengthens the surface. Our inside frosted silvered bulb, though given no other strengthening treatment, is adequately strongi for shipment and commercial use in general.

The objects of the invention and the features and methods through which they are attained will best be understood and appreciated from the following description of the best embodiments at present known as illustrated in the accompanying drawing.

The figures of the drawing are sectioned for glass as the base material for the reflector but this is for illustration in connection with a use of the invention in incandescent lamps and is not to be construed as limiting. In the drawing;

Figures l and 2 show, respectively, a pre-treatment of the base material by frosting and a reflecting medium is then applied to such frosted face, as by silvering;

Figs. 3 and 4 show, respectively, one face of the base material prepared for retaining an irregular surfacing of the reflecting medium and such surfacing then applied;

Figs. 5 and 6 show, respectively, a modification of the treatment shown by Figs. 3 and 4 in that the prepared base material is given its uneven reflecting surface by a special treatment thereof;

Figs. 'I and 8 show, respectively, a modification of the treatment shown in Figs. 1 and 2 in that the base material is first molded to an Auneven matrix prior to applying a reflecting medium to a face thereof:

Fig. 9 is illustrative of an incandescent lamp provided with a diffusing reflector made in accordance-with the teaching of this specification; and

Fig. 101s a view of an incandescent lamp similar to Fig. 9 but showing a modified form of reflector for reflecting both diffused andy non-diffused light.

Referring to the drawing, l0 represents a 4section of' a suitable l base material for a reflector or for a mirror which may be a part of the glass bulb of an incandescent lamp. The four pairs of figures from 1 to 8 illustrate fou'r methods of procedure to produce a diffusing reflector on the base material. These will be described in their application to the production of reflecting lamp bulbs as a specific example of use within the broader scope of the invention.

Method I (Figs; 1 and 2) The interior of the bulb may be frosted by a pre-treatment with hydrofiuoric acid in the manner regularly employed in the industry for ordinary non-reflecting bulbs except that a single etching process is suillcient as above described.

The frosted area may be the entire inside surface of the bulb, or it may be co-extensive with the reecting surface, or it may be of less extent than the reflecting surfaceV which will be obtained by silvering at a later operation. It is preferable, from the standpoint of efficiency. to leave the light transmitting area of the bulb unfrosted but for certain purposes it may be desirable to frost the light transmitting part of the bulb beyond the diffusing reflector, so that the bright filament will not be directly visible from any'angle. A thin coating of metallic silver deposited on the microscopically roughened surface forms a rougher matte surface than when deposited on the smooth glass; in fact it pax-takes almost exactly of the nature and contour of the minute craters and pin holes which have been etched into the surface of the glass by the hydroluorlc acid. While the surface appears to be macroscopically smooth the rugosities thus formed are readily visible under the microscope.

This minutely lirregular surface of metallic silver is still silver and it still 'reflects with the high coefficient of reflection that any silvered surface does, but it reflects a diffused light.

The coating resulting from this method of 'solving the problem gives a white appearance to the outside of the bulb, even whiter than an unsilvered frosted bulb. For certain purposes this may well be an advantage in that the bright diffusing reflector is not visible through the glass.

Under some conditions, as in the case of an asymmetric bulb designed for a special purpose, it may not be dsirable or necessary to form a light diffusing surface over the entire area of its reflector. In such a case the reflector would consist of a combination of selected areas for refiecty tages it is not the preferred method. There is always the danger of the unprotected silver becoming defaced, as by scratching, during .the period of use, and it will tarnish and eventually deteriorate. A protector against these eventualities may be provided but this is expensive and for many uses undesirable. Moreover the light,

in order to be reflected from the silvered outside surface of the bulb, must rst pass through the glass and in the case of inside frosting must pass through the glass twice. 'Ihis causes a real loss of lighting emciency.

Method II (Fig. 3 and 4) disclosed in the mentioned Deren application, and l then at the end of the period when an adequate deposit of the fine crystals has taken place, the shaking motion imparted to the bulb and its contents is stopped. and the continued deposition of silver is allowed to proceed while the bulb is at rest. This builds up a relatively thick and irregular deposit upon the rst coating which appears under the microscope to be composed of large crystals, and crystal masses. vThese large relatively irregular crystals have the same excellent high coefficient of reflection as any other pure silver coating, Abut are actually sufficiently large and irregular to reflect a diffused light. It has been found that this relatively coarse crystal deposit adheres better to the glass if it is deposited upon a finer coating of silver, but this method is not limited to this combination of layers since satisfactory diil'using reflectors may be made by a coating of coarse silver crystals directly onto the base material.

Method III (Figs. 5 and 6) This method consists in depositing a regular fine coating of metallic silver, as described in said co-pending application Serial No. 42,227 of Pincus Deren, and then making this relatively smooth surface somewhat coarser and rougher by attacking it with a chemical substance that will change part of the silver to a compound of silver. Since the very fine crystals of which the metallic silver layer is composed fit very closely together, and may even overlap in places, it is vapparent that by changing some of these crystals and/or parts of some of these crystals to a compound containing a greater weight of matter and of lower specific gravity than the heavy metallic' silver, the volume of the silver coating will be considerably increased. This effect will be manifest by an irregular raising of parts of the surface of the deposit and the development oi' what appear to be larger crystals. 'Ihe color of the deposit may change somewhat, depending on what the treatment is. For example, if the freshly silvered bulb is filled with a solution of sodium chloride there will be a gradual change of the surface layers of the silver coating from silver to silver chloride. Red phosphorous in water suspension introduced into the bulb will gradually attack the surface oi the silver deposit, particularly if a trace of nonoxidizing mineral acid, for example hydrochloric. is added to the water. Air containing a very low concentration of chlorine, or other halogen, may

be admitted. into the dry bulb and again part of the silver deposit is changed to silver chloride.

Method 1v maar and s) This method of forming a highly efficient reector producing diffused light may be carried 'out 4 andere by using special molds or matrices in which the bulbs are blown. Any repeated pattern or a series ofageometric lines may be cut into or raised upon the bulb mold, such as a pattern made by forcing ties of frosting, can then have a thin smooth coat c' of metallic silver applied thereto and as this providesy a roughened or uneven refiectingu'surface Y a diffusing reflector will result.

Adifi'using reflector made under any of these methods greatly increases the amount of diffused light emanating from such a reflecting surface occupying a definite and predetermined part of the surface of the bulb of an incandescent lamp, and so avoids either the projection of a partially focused image of the filament ory its shadow, and

without necessarily causing the light to be transmitted through a frosted or otherwise diffusing surface with its consequent loss of efficiency. y

This difference in'lighting efllciency is shown by the following laboratory data, typical of many such comparisons that have been made. The bulbs of the two lamps compared were as nearly alike as possible in all respects, except that the bulb of lamp B was frosted over the light-transmitting, non-silvered area only, and the bulb of lamp A was fronsted under the silvered area only. Both were 150 watt reflecting and diffusing lamps, but lamp A obtained diffusion by reflecting from a diffusing inside reflector with a microscopically 40 roughened surface the light being transmitted through unfrosted glass, while lamp B reflected from a bright plain inside reflector and obtained diffusion by transmitting the light through frosted glass. 'I'he light falling on the test table was substantially equally diffused and both luminous fields were substantially uniform as to intensity of illumination. y l

The lamps were tested in the same socket, permanently fastened at a constant distance above 5o the test table. The actual foot-candles rof il lumination falling on the table were measured directly under the lamp and at one half foot distances measured in a straight line along the table away from this point.

- Lamp A dlf- Dimnf "331 omt fusing-reflector Lamp ll frosted over transi rfcty u er amp type, iootmittng area, foot-candles n candles 00 0.o- 4s. o 41.0 0. 50. 0 42. 0 i. 42.5 41.0 1.. 37. 5 37. 5 2. 33.0 31. 5 2. 27. 5 26. 0 3. zi. 5 22. (l 20.0 18. 1S. 0 14. 0 14. 5 12. 0 11. 5 10. 0 9. 5 8. 0

120 120 Current require- 1.265 1.275 ments oi lamps 161.8 153.0 during the test.

Thus, in this comparison, despite the fact that the prior art lamp B, obtaining diffusion by trans- 75 mitting through a frosted area, was of slightly higher wattage rating, it actually emitted less light. The sum of the foot-candles in each of the columns is a rough comparative measure of the total amount of light emitted. On cornpar-K ing these sums it is apparent that the newdif-v v fusing-reflector lamp `A of this invention emits about 10% more light than the old reflecting and diffusing lamp B.

While silver has been named as a metal suitable' for a reflecting coating it isy contemplated y10 that other metals may beemployed within the scope of the invention. For example, nickelrnay be used, or chromium may be deposited upon a thin priming coat of silver. f

Fig. 9 of the drawing shows an application of 15 the invention to an incandescent rlamp used yfor direct lighting. As illustrated the-diffusing rey sector l2 is of sufficient depth no hood the mament i4 the lower boundary of the reflector being so located relatively to the filament that the 20 light rays may spread to an approximate 60 cone, indicated by dotted lines, hereinbefore described as having been found to constitute an eflicient fleld of useful light. With the use, of a diffusing reflector the portioni ofthe bulb wall 25y through which the light shines may be clear glass as shown. The figure shows a reflecting disk il, preferably of metal, and located between the'flla-` f ment and seal of the lamp serving, among other functions, to reinforce the useful light emitted 30 by deflecting the rays or beams heretofore lost in the neck of the lamp, as disclosed in the co l pending application of Clarence Birdseye Serial No. 33,694, flied July 29, 1935whlch is Patent 2,142,104. This reflecting disk, when used with sa the diffusing reflector I2, would also preferably be convertedto a diffusing reflector by one of the methods described herein or its equivalent.

Fig. 10 illustrates, byway of example, an incandescent lamp provided with a reflector that 4o reflects a diffused light from one part and a nondiffused light from another part. The bulb shown is provided with an inside diffusing reflector I2 like that shown in Fig. 9 and with an added plain or specular reflector 20 in the form of an annulus 45 at the lower edge of the reflector I2. The position of the specularly reflecting portion withrer y f lation to the diffusing portion may be varied. It may be added to or it may partly impinge upon or be wholly surrounded by the diffusing reflector according to the conditions under which the lamp is to be used, for example, spot lighting a particular object or increasing the illumination over a special area.

When the specularly reflecting portion is in the position shown in Fig. 10, namely, an annulus at or about the region of greatest diameter of the bulb, it serves to increase the illumination over a ring at the periphery of the illuminated field where it would otherwise be less than at the a0 center. At the same time it also serves to narrow the field somewhat. The net effect is to give a more uniform illumination over a narrower fleld instead of a less uniform illumination over a wider field. When the specularly reflecting portion is 35 otherwise disposed it gives a different effect, predictable from its position relative to the filament.

From the foregoing description and from the appended claims it will be understood that dif- 10 fusing reflectors to be manufactured from the teaching of this invention arenot limited as to size, shape or location -with respect to the source of light and may be employed with lamps varying widely in type and power. In its application u or capable of diffusing light simultaneously with its reflection from a reecting surface, particularly an internal reflector and light diffuser.

It is believed that a reflector of this type, having a surface. of high reflective index and with this surface minutely roughened in a manner readily discernible under a microscope, and for the purpose of reflecting a diffused light from a high temperature concentrated source, and without transmitting thisl reflected light through a diffusing medium which always incurs losses, has not been heretoforeavailable.

The nature and scope of the invention having been indicated and preferred embodiments and methods of manufacture having been specifically described, what is claimed as new, is:-

1. The method of making light diffusing lamps having a high temperature source of light which comprises applying a substantially smooth coating of silver to a. surface of the lamp and then treating the exposed surface of said coating in a manner to create -surface rugosities.

2. The method of claim 1 in which the said treatment consists in superimposing an irregular deposit of relatively large silver crystals and silver crystal masses on said first coating of silver.

3. The method of claim 1 in which the said treatment consists in attacking the outer layers of said coating with a chemical capable of converting the treated parts to a compound of silver 3,-,` thereby obtaining an uneven development of larger` crystals throughoutthe treated parts and thus raising such parts irregularly above the surface of said coating.

4. The method of claim 1 in which the said treatment consists in increasing the volume of the silver in said coating throughout parts of its surface thereby raising said parts above the surface of said coating. n f

5. The method of making light diffusion lamps having a high temperature source of light which comprises coating a surface of the lamp with a deposit of silver crystals sufficiently large and irregular to produce a surface capable oi' reflecting a diffused light. 6. An incandescent lamp including in its structure a'bulb and alight source and having a metallic reflecting medium applied to the inner surface of part of thev area of the bulb, the reflecting medium having its exposed surface uneven so that light reflected thereby isl diffused, said n inner surface ofthe bulb to which the reflecting medium is applied being smooth and even and the exposed surface of the Vreflecting medium being rough and uneven.

7. Anv incandescent lamp having a reflecting disc positioned between the source of light and the seal of said lamp, said disc havingits reflecting surface roughened by minute irregularities so that it reflects a diffused light.

8. An incandescent lamp having a reflecting disc positioned between the source of light and the `seal of said lampand having a reflecting medium applied to a predetermined area of its bulb, the reflecting surfaces of both disc and bulb reflecting -a diffused light by virtue of minute irregularities extending thereover.

9. An incandescent lamp comprising a bulb,

having a lament-of concentrated. spiral form therein, the inner surface of said bulb being provided with a. reflecting surface from a point on the neck of said bulb to the region of greatest diameter of said bulb, an annular portion of said reflecting surface in the region of greatest'dlameter of said bulb being specularly reflecting in character and the remainder of said reecting surface being diiusely reflecting in character, the lament being placed substantially at the Afocus of said diifusely reflecting portionlof said reflecting surface, and the plane angle subtended at the filament by that boundary of the specularly 'reflecting surface which is furthest from the neck of said bulb being substantially degrees.

10. An incandescent lamp as in claim 9 in which the'dlifusely reflecting surface consists of a nlm of metal of substantially uniform thickness adhering closely to the roughened inner wall of the bulb.

11. An incandescent lamp as in claim 9 in which the diifusely reflecting surfaceI consists of a film of metall adhering to the smooth inner wall of the bulb, the exposed surface of said film being rough. I

CLARENCE BIRDSEYE. PINCUB DEBEN.

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