US2204399A - Reflecting electric lamp - Google Patents

Description

June 11, 1940.

C. BIRDSEYE El '1 REFLECTING ELECTRIC LAMP Filed Nov. 25, 1938 114 U6 11 W0 2 deg/1444c 162L411? Patented June 11, 1940 UNITED STATES REFLECTING ELECTRIC LAMP Clarence Birdseye and Pincus Deren, Gloucester, Mass., assignors, by mesne assignments, to

Birdseye Electric Corporation,

Gloucester,

Mass., a corporation of Massachusetts Application November 25, 1938, Serial No. 242,216

6 Claims.

The present invention relates to electric lamps and consists in an improved reflecting lamp having certain advantages over those heretofore available. The invention includes within its scope the process herein disclosed of producing such improved reflecting lamp. In reflecting electric lamps in which the light source is hooded by a reflecting surface formed upon the bulb there is a tendency for the reflected rays to project a shadow of the mount and filament supports or an image of the incandescent filament and to produce thereby a light pattern that is irregular in intensity and unpleasant to the eye. Heretofore this objectionable tendency has been eliminated to some extent by frosting the transmitting area of the bulb either on the inside or the outside. The frosted transmitting area diffuses the light emitted by the bulb so as to eliminate or largely reduce uneven light intensity patterns cast on the illuminated area.

There is however a serious objection incident to the practice above discussed. When practically all the light rays from the incandescent filament are directed by the reflecting surface through the transmitting area of the bulb the concentration of light is so great that the glass of the bulb in this area, when frosted in the usual commercial manner, becomes intensely brilliant. This frosted transmitting area even becomes so bright that, particularly in lamps of high wattage, it is unpleasant to observe directly despite the fact that the filament may be completely hooded by the opaque reflecting portion of the bulb. In fact a lamp frosted for direct illumination inthe customary manner when viewed from the side is very much brighter throughout its tfinsmitting area than a similar lamp without any frosting.

In our prior Patent No. 2,144,673, granted January 24, 1939, of which the present application is a continuation as to all common subject matter, We have disclosed a method of preventing the formation of shadows and bright images in the illuminated areas by applying a diffusing reflector to the surface of the bulb. In one aspect the present invention consists in an improvement over that disclosed in our said prior patent. viz. we control the diffusion of the reflected light by a combination of two cxpedients each however modified to an extent that would make either of them alone inadequate for the purpose, and

- which at the same time, avoids certain very real the entire inner surface of the bulb is processed so that it presents a continuous contour of smooth shallow rounded depressions, the reflecting coating being applied to this surface in the desired areas as metal deposited or evaporated directly upon the processed surface of the bulb and thereby given a diffusing reflecting characteristic. The configuration imparted to the bulb by the suggested treatment is hardly adequate to give to the metal deposited upon it a pronounced difiusing character sufiicient to eliminate shadows, nor will the same treatment of the transmitting area accomplish this end by itself. However, by combining the diffusing reflecting surface thus produced and the diffusing transmitting surface in cooperative relation, so that their individual effects are additive, the final result is highly satisfactory in eliminating shadows in the illuminated area. Moreover, this is accomplished without causing the transmitting area to glow with a high degree of brilliancy. Further, the processed transmitting area diverts but a slight amount of light as compared to the amount which is lost in a corresponding area which has been commercially frosted and there is practically no loss of light within the lamp at any point of diffusing reflection since the metallic coating preferably may be applied to the inner surface of the bulb so that no loss occurs on account of the passage of light through the-glass to and from an exterior reflecting surface.

Our invention includes within its scope a novel andimproved process of producing the reflecting bulb above discussed. The process of our invention is characterized by first processing the inner surface of the bulb in the manner described, then applying a metallic reflecting coating to the internal processed surface and finally removing the metal coating by means of a chemical solution to define a transmitting area in the lamp. Heretofore it has been the general practice when applyinga reflecting coating of silver or aluminum to the internal surface of lamp bulbs to coat sub-' in the case of silver coating or caustic soda in the case of aluminum coating.

These and other features'and characteristics of our invention will be best understood and appreciated from the following description of one manner of practicing the process of our invention and an illustrative example of a reflecting electric lamp embodying our invention. In the drawing- Fig. 1 is a view in elevation, with parts broken away, suggesting the step of depositing a metallic reflecting coating upon the inner surface of a processed bulb, and includes a section of the bulb wall as seen magnified approximately 500 times in the fleld of a microscope;

Fig. 2 is a similar view suggesting the step of removing the metallic coating from the transmitting area of the coated bulb, and

Fig. 3 is a view in elevation of the complete lamp, and also includes a section of the bulb wall as seen in the field of a microscope.

The first step in the process of our invention is to provide substantially the entire inner surface of the bulb with a particular configuration of contour which, for want of a better term, we will call a shell surface. By this we mean a contour of shallow rounded depressions or hollows which covers substantially the whole surface, and has no deep valleys, no sharp peaks and no flat facet faces, but merely gently scooped and rounded depressions. The individual depressions or hollows are of varied size, irregular in shape and appear to be bounded by straight or slightly curved lines extending in all direction and meeting in vertices sometimes in pairs and sometimes in greater numbers. In Fig. 1 the characteristic surface is represented as actually observed in the field of a microscope at a magnification of 300 to 500. Heretofore frosting imparted to bulbs has been characterized by deep cavities with steep sides which under the microscope look in some places like the facets of crystals and in other places present sharply concave surfaces. These actually act to reflect the light back and forth from side to side of the pits or cavities and create much greater disturbances and absorption of the light than does the type of configuration employed in accordance with our invention. Our novel configuration of surface, on the contrary, does not substantially interfere with the directional characteristics of the lamp, that is to say, the reflecting surfaces of the lamp define the beam in which the light is emitted and the reflecting or diffusing effect of the shell surface is not such as to deflect any substantial amount of light outside this beam. The effect we desire is a slight differential refraction of the light passing through the transmitting section of the bulb in a heterogeneous manner, that is, the

emergence angle 'of each ray is only slightly different from the straight line it would follow in emerging from an unprocessed bulb.

The present commercial process of frosting bulbs is fully disclosed in U. S. Letters Patent No. 1,687,510, October 16, 1928, Pipkin. The process of that patent involves the use of two' different frosting solutions of the same composition, the

second used being merely weaker than the first.

' from any frosted surface known before our discovery and as such constitutes an important aspect of our invention.

Having first provided the desired shell surface in the bulb, the next step of the process is to apply a metallic reflecting coating thereto. One process of applying such metallic coating is dis closed in our copending application, Ser. No. 191,493, filed-February 19, 1938. In Fig. 1 is illustrated the step of vaporizing silver or aluminum to form a reflecting coating in the manner more fully disclosed in our said application. The processed bulb I is inverted over a pair of electrodes H and i2, sealed and exhausted. Between the electrodes is mounted a boat or receptacle l3 in which is placed a charge of metal for the coating. The exhausted bulb is heated and the metal charge reduced to a molten state while the bulb is maintained under vacuum so that any gases evolved from the metal charge are immediately removed from the bulb. The charge in the boat I3 is then quickly raised to the vaporizing point of the metal by electrical energy transmitted to the electrodes H and I2. The metal is thus flashed and deposited upon the shell surface of the inner walls of the exhausted bulb.

In this operation a diffusing reflecting surface is formed of the general character disclosed in our prior Patent No. 2,144,663 already identified. The'structure of this reflecting surface is indicated in Fig. 3 of the drawing from which it will be seen that the gently sloping rounded hoilows and depressions of the shell surface are now coated with a thin deposit of metal l9 thereby forming a reflector which is mildly diffusing, that is to say, in which the reflected rays are slightly but not violently deflected from the normal paths which they would follow if specularly reflected from the surface of unprocess walls. Our object is to provide a reflecting surface having a relatively slight diffusing action which is combined in its effect with the relatively slight diffusing action of the shell surfaced transmitting portion of the lamp. The cooperative effect of these two factors produces the desired results in eliminating shadows and bright images in the area illuminated by the lamp.

The next step in our process consists in removing the reflecting coating from a selected area of the bulb to define a shell surfaced transmitting portion therein. The metallic coating may be removed in accordance with the process of our prior application, Ser. No. 177,780, filed Decem her 2, 1937. In that process a solvent solution is applied to those portions of the bulb from which it is desired to remove the metallic coating. We have suggested in Fig. 2 the step of removing metallic coating from the bowl end of a bulb intended for use in direct lighting. The coated bulb Ill is supported in upright position and the solvent solution is supplied through a vertical tube l5 surrounded by a larger tube or casing l6 and containing concentrically a smaller withend of the tube l'l within the delivery tube l and acts to prevent splashing of the solvent solution as it is supplied to the bulb up to substantially the level of its maximum diameter. If silver is employed as a coating for the bulb an acid solution, such as nitric acid, may be delivered through the tube 15. If aluminum is used as the metal of the coating a strongly alkaline solution may be similarly employed. As soon as the coating is dissolved the solution is withdrawn through the innertube l1 and the bulb immediately washed out, with the result that a sharp line of demarkation is formed between the silver coating [9 and the bare shell surfaced transmitting portion 20 of the bulb.

Having completed the shell processing and metallic coating of selected areas of the bulb in the manner above explained the bulb may now be employed in the manufacture of an electric reflecting lamp by following the conventional steps of manufacture. The mount 21 and filament are sealed into the bulb neck with the filament substantially hooded by the reflecting coating i9. Preferably the filament will be of the coiled coil type supplying a concentrated light source. The bulb is then exhausted, gas filled if desired, and sealed preparatory to being equipped with a metal base 22- of any desired commercial construction. It will be understood that the shallow rounded depressions making up' the shell surface of the bulb are actually infinitesimal in size. The processed surface is of a somewhat lustrous light gray or pearl color in appearance and noticeably more transparent than a frosted surface. The surface as illustrated in Figs. 1 and 3 is' drawn from microphotographs taken at a magnification of 500 diameters and then enlarged in the reproduction. In addition to providing an electric reflecting lamp supplying a substantially uniform light pattern and one in which the transmitting portion of the "lamp is not objectionably brilliant when the lamp is in use, we have substantially increased the illuminating efliciency of the lamp by reducing the amount of light absorbed and diverted in its transmitting portion as compared with lamps heretofore commercially available. The intensity of illumination derived from a lamp constructed in accordance with our invention is about 16% greater than that derived from a commercially frosted lamp of identical size and rating.

I While it is not practicable completely to remove a metallic coating from a shell surface by mechanical means, it is possible by using a scraping tool to form a translucent spiral or other markings in the coated area of a bulb processed as herein disclosed if it should be desired to secure the luminous appearance of the coated portion of the bulb as disclosed inthe prior patent of Birdseye, No. 2,074,888, March 23, 1937.

Having thus described our invention what we claim as new and desire to secure by Letters Patent of the United States is,

1. A reflecting electric lamp comprising a bulb having an interior surface with a shell configuration of contour, a metallic coating covering portions of said surface and presenting a roughened diffusing reflecting surface which limits and defines a shell surfaced transmitting area in the bulb, and a light source hooded within the reflecting area.

2. A reflecting electric lampcomprising a light source and a bulb having a diffusing metallic reflecting surface, in combination with a diffusing transmitting portion in the bulb, neither of which processed to present shallow rounded concavities contiguous to each other and of infinitesimal size, a metallic coating covering a portion of the processed surface and presenting a diffusing reflector for concentrating and directing the light of the lamp in a beam, and defining by its edges an uncoated processed transmitting area through which the light beam is directed and by which its rays are slightlydiffused without pronounced illumination of the glass of said transmitting area.

4. A reflecting incandescent lamp comprising a bulb having a shell surface partly coated with a metallic reflector and uncoated in a transmitting' area, said lamp providing a practically shadowless illumination substantially 16% more intense than a lamp otherwise similar but with a commercially frosted transmitting area.

5. A glass electric lamp bulb having its entire interior surface frosted by etching so that the maximum brightness of an ordinary incandescent lamp comprising such a bulb will be more than twenty-five per cent of that of said lamp with a clear bulb, said interior bulb surface being characterized by the presence of shallow as distinguished from pronounced depressions and having a reflecting metallic coating upon a portion of said surface and rendered diffusive thereby,

and an uncoated transmitting portion.

6. An electric incandescent lamp having a glass bulb provided with a shell surface, that is to say, a glass surface which when observed at a magnification of 800 to 500. appears to comprise shallow rounded contiguous depressions or hollows, varied in size. irregular in shape and bounded by slightly curved and straight lines extending in all directions and meeting at vertices sometimes in pairs and sometimes in greater numbers, and. a metallic reflecting medium applied as a coating of substantial thickness to said shell surface thereby presenting a diffusing reflecting surface in the lamp. I

CLARENCE BIRDSEYE.

PINCUS DEREN.

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