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Publication numberUS2109056 A
Publication typeGrant
Publication dateFeb 22, 1938
Filing dateDec 28, 1936
Priority dateDec 28, 1936
Publication numberUS 2109056 A, US 2109056A, US-A-2109056, US2109056 A, US2109056A
InventorsBardwell Cecil, Carl R Erickson, Jess C Rose
Original AssigneeMotion Picture Electric Produc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Studio lamp
US 2109056 A
Abstract  available in
Images(3)
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Claims  available in
Description  (OCR text may contain errors)

Feb. 22, 1938. c. BARDWELL ET AL STUDIO LAMP Filed Dec. 28, 1936 3 Sheets-Sheet 1 Inventor, Cecil Bardwell. Carl E. Erickson.

Jess C. Rose.

Allorney.

Feb. 22, 1938. c. BARDWELL ET AL STUDIO LAMP Filed Dec. 28, 1956 5 Sheets-Sheet 2 .fw I

43 Inventor.

Cec

z'Z Bardwell.

Carl R. Erickson.

Jess 6'. Rose.

.flfiorney.

Feb. 22, 1938. c. BARDWELL ET AL 2,109,056

STUDIO LAMP Filed Dec. 28, 1936 5 Sheets-Sheet 3 /o4 ma we /oz m5 lnvenior. Cecil Bardwell.

Carl K.Erickson.

Jess C. Rose.

Patented Feb. 22, 1938 I UNITED STATES PATENT OFFICE STUDIO LAMP Cecil Bardwell, West Los Angeles, and Carl R. Erickson and Jess 0. Rose, Los Angeles, Calif., assignors to Motion Picture Electric Products, Los Angeles, Calif., a corporation of California Application December 28,1936, Serial No. 117,796

6 Claims. (Cl. 240-413) This invention relates generally to studio flood is equipped with a condenser lens, preferably, and spot lamps such as are used in motion picthough not necessarily, of the echelon or Fresnel ture studios for illumination of sets, and more type, in place of the usual spill ring, and a small particularly to lens and reflector arrangements in spherical reflector is placed directly back of the such lamps. incandescent lamp. The small spherical reflec- 5 The ordinary studio spot lamp comprises an intor forms an image of the filament of the lamp candescent light globe or lamp that is movable in the plane of the filament itself, and thus intenforwardly and rearwardly along the axis of a sifies the light available at the source. Without parabolic reflector, the lamp throwing a small this spherical reflector the lamp is much superior 10 spot of light when the light'globe is near the focal to a conventional spot and flood lamp, but there 10 point of the reflector, while flood characteristics is a substantial gain in intensity and uniformity are obtained when the globe is moved near the of field with its use, and in the preferred form reflector, i of the invention this spherical mirror is used.

A device known in the art as a spill ring, con- Light from the filament and from the filament sisting of a series of spaced concentric sleeves, is image produced by this spherical mirror is radi- 15 placed in front of the incandescent lamp, the ated rearwardly in the lamp around the spherical purpose of this device being to eliminate leak mirror and .strikes the main reflector which may lightthat is, light rays which would otherwise for instance be of parabolic form, and is reflected leave the lamp at such an angle as to cause undeor projected by this reflector to the field. Light sirable illumination outside of the field desired radiated forwardly from the filament and fila- 20 to be covered by the lamp. A spill ring of the ment image is gathered by the condenser lens in type mentioned is shown in an application of front and projected toward the field. The front Jess C. Rose, Ser. No. 22,546, filed May 21, 1935, condenser lens is of such a nature as to proentitled Focusing means for incandescent studio J'ect this light with a high degree of uniformity spot light. over the field covered thereby, and to do this Astudio lamp of the reflector type, fitted with without producing leak light. Using the same a spill ring, such as is now standard in present lamp casing, main reflector and incandescent day studio practice, has a fairly sharply defined lamp with which the test figures given above were light field, but under 'floodlight conditions obtained, and simply removing the spill ring and 0 the light field is dark in the center. For exadding the condenser lens and spherical reflector ample, assuming a 24 inch reflector lamp and a in accordance with the present invention, the 5 k. w. light globe positioned at flood, the globe illumination at full flood adj st t at a disbeing provided with a usual spill ring, the illumitance of twenty feet is 250 foot candles at the nation near the boundary of the light field at a edge of the field and 270 foot candles at the cen- 5 distance of twenty feet is approximately 165 foot ter of the field. And at the part flood position,

candles, while at the center of the field the i11u-- the illumination at the edge of the field is 540 mination is only about 55 foot candles. At a. foot candles, and at the center of the field is 585 part flood position, the illumination near the edge ot a h s s to e Compared ith 165 of the field is about 485 foot candles, and in the foot candles at the edge of the field and 55 foot center of the field is about 100 foot candles. candles in the center for full flood, and 485 foot 40 Without the spill ring there is so much leak light candles at the edge of the field and 100 foot that it is impossible to illuminate the set properly. candles at the center for the part flood position, It is a primary object of the present invention using an incandescent lamp of the same wattage to provide a studio spot and flood lamp capable in the old type studio lamp. v of projecting a sharply defined beam or fleld of As a further feature of the invention, focusing 5 light, which is at the same time characterized by means are provided for moving the incandescent a high degree of uniformity of intensity across lamp and projection, lens in such a manner as the field. tomaintain similar focus relations between the A further object of the invention is to provide incandescent lamp and stationary reflector and a studio spot and flood lamp which yields a higher the incandescent lamp and the projection lens, 50 intensity of illumination, both at spot and flood, so that at both spot and flood as well as at all without increase in the candle power or wattage intermediate positions the light source has the of the incandescent lamp. same focus relations with the lens as it has with In accordance with the present invention, a the reflector. studio spot and flood lamp of the reflector type The invention will be more fully understood 55 from the following detailed description of a present preferred embodiment thereof, reference for this purpose being had to the accompanying drawings, in which:

Fig. 1 is a longitudinal vertical medial section of a lamp in accordance with the present invention, parts appearing in elevation, the lamp being shown adjusted to full flood position;

Fig. 2 is a view similar to a portion of Fig. 1, but showing the lamp in spot position;

Fig. 3 is a section taken on broken line 3-3 of Fig. 2;

Fig. 4 is a section taken as indicated by line 4-4 of Fig. 1; and

Fig. 5 shows a modification of the lens focusing means.

The lamp, generally designated by numeral I0, is made of front and rear ring frame members I I and I2, respectively, formed with inwardly extending flanges I3 and i4. Mounted within flanges l3 and I4 are two substantially semicylindric shell or side wall members 16. The 1 lower edges of these side wall members define an opening which communicates with the interior of a rectangular case or box l8, said box being mounted on the lower portion of the lamp housing in any suitable manner. This casing member or box i8 is designed to house certain operating mechanism for the focusing mechanism, etc., and may be considered as apart of the lamp frame.

Rearward ring frame l2 has an opening 22 adapted to receive a rear annular closure member 23 carrying a usual curved reflector 24. This reflector may be either a glass mirror or a polished metal reflector, and is preferably parabolic in character, though other shapes, such as ellipsoidal, might be used and are to be considered as the equivalent, insofar as the broad invention is concerned, of the parabolic mirror specifically mentioned. To distinguish this reflector from a subsequently mentioned small spherical mirror or reflector, this reflector 24 may be referred to as a projecting reflector. The lamp has a crowned back member 24a which is secured to member 23, as shown.

Front frame ring I i is shown provided with an annular opening 25 which receives a carrier ring 26 in which is mounted front glass member 21. This front glass is useful when the lamp is to be used out of doors under unfavorable weather conditions to shut out rain, etc. This plane front glass is also interchangeable with a diverging glass, of any well known type. However, ordinarily such front glass members are not required.

The incandescent lamp is designated at 30, and is shown mounted on a carriage 3i which is adapted to slide forwardly and rearwardly, on the axis of mirror 24, on a pair of parallel guide rods 34 and 35 suitably mounted at their ends in the lamp housing. As clearly shown, these rods are parallel to the axis of mirror 24 and are in a common horizontal plane. Carriage 3| is provided with a bearing 31 which slides freely on guide rod 35, and with forward and rearward bearings 38 and 39 which slide freely on guide rod 34.

Mounted forwardly of incandescent lamp and coaxial with reflector 24 is a condenser or projection lens 40. This lens 40, described in more detail hereinafter, is mounted within a carrier ring 4| supported on the upper end of a carriage 42 also slidable on rods 34 and 35. This carriage 42 is provided with a bearing 43 slidable on rod 34, and with a pair of bearings 44 and 45 slidable on rod 35, the parts being arranged as shown in Fig. 3, so that each carriage has a three-point support on the rods, while the two carriages overlap each other somewhat, as indicated. Carriage 3i has mounted thereon an upwardly extending bracket 48 supporting a small spherical reflector or mirror 49 to the rear of and concentric with light globe 30.

As a typical example of the relative dimensions of parts, but without intention of limiting the invention, it may be stated that for a 24-inch lamp, that is, a lamp having a rear parabolic reflector 24 inches in diameter, and using a five k. w. incandescent lamp, condenser lens 40 is 10 inches in diameter, and spherical reflector 49 is 5% inches in diameter, and is positioned with its center of curvature corresponding substantially with the center of the filament f of light globe 30.

Means are provided for sliding carriage 3| back and forth on rods 34 and for the purpose of adjusting the incandescent lamp carried there by between spot and flood positions with reference to parabolic reflector 24, and for simultaneously effecting relative movements between condenser lens and lamp 30 of such a character as to correspondingly regulate the focus of lens 40 between spot and flood conditions. One simple and preferred means for accomplishing such co-relative movements of lamp 30 and lens 40 will now be described.

A horizontal operating shaft 50 is rotatably mounted in side wall 5| of box I8. This shaft, which is located below guide rods 34 and 35, has tightly mounted on its inner end an arm 52, the swinging end of which is pivotally connected to one end of a link 53, and the other end of link 53 is pivotally connected at 54 with lamp carriage bearing 39. The outer end of shaft 50 is provided with an operating knob 51 provided with handle 58 and pointer 59, the latter moving over a suitable scale formed on a scale plate 6| aflfixed to the outer surface of wall 5|.

It will be evident from a consideration of Figs. 1 and 2 that the full range of forward and rearward movement of light globe carriage 3| is accomplished by a 180 rotation of shaft and arm 52. The carriage is in its rearmost (floodlight) position when arm 52 is in a horizontal rearwardly extended position and is in its extreme forward (spot) position when arm 52 is in a horizontal forwardly extending position, the filament of lamp 3!] being substantially at the focal point of reflector 24 in the latter position. The range of movement of the lamp carriage is of course determined by the length of arm 52, and link 53 is of such length that it will place the carriage and lamp in correct full flood and spot positions in the two described positions of arm 52.

In Fig. 1 lamp 35 is in its rearmost position, up close to the reflector 24, so that the light reflected from 24 is spread out or in other words given flood characteristics. At this time, condenser or projection lens 40 is in a position relatively close to lamp 30, at which position light rays from the filament of lamp 3!! are also spread out or given flood characteristics. Now, as lamp 30 is moved forwardly toward spot position with relation to deflector 24, it is necessary to move condenser 40 also forwardly, and condenser 45 must not only be moved forwardly with relation with reflector 24, but it must be moved forwardly with relation to forwardly moving lamp 30, so that when lamp 30 is at spot position, at substantially the focal point of parabolic reflector 24, condenser 40 will be moved forwardly with reference to lamp 30 sufficiently that light rays from the lamp fllament passing through lens 40 will be refracted into a parallel beam, so as likewise to project a spot". It will thus be evident that it is necessary to move lens 40 in the same direction as lamp 30, but at faster speed, in order that the lamp will have the same focus relations to both reflector 24 and condenser 40 at all of its positions.

Accordingly, as here typically shown, there is provided a lever 10, mounted at its lower end on a horizontal shaft ll extending transversely of rods 34 and and pivotally supported in brackets 12 and 13 mounted on the lower wall 14 of box I 8. To the upper end of this lever 10 is pivotally connected the rearward end of a link 16, the forward end of which is pivotally connected, as at IT, to lens carriage 42. Connected to lever III at a point intermediate its ends is the forward end of a link 80, the rearward end of which is pivotally connected at 8| with lamp carriage 3|. Lever I0 is thus a motion multiplying lever, the pivotal connection point between lens carriage operating link 16 and said lever being outside of and moving with greater speed than the pivotal connection point between link 80 and the lever. In the present illustrative embodiment of the invention, link 80 is connected to lever 10 at a point two-thirds of the distance from the pivotal mounting of said lever to the connection point between the lever and link 16, although this will be varied depending upon the particular optical characteristics of the lens and reflector used in any given lamp.

Rotation of focusing handle 58 swings arm 52, which acts through link 53 to move light globe carriage 3 l, and such movement of the light globe carriage is transmitted through link 80,

multiplied at lever Ill, and then transmitted through link 16 to move lens carriage 42 and the lens in the same direction as the light globe but at higher speed. While in the present illustrative embodiment of the invention light globe carriage 3| constitutes a part of the operative interconnection between manual operating handle 58 and lens carriage 42, it will be evident that this is not essential. In any instance, however, there is a driving interconnection from manual operating handle 58 leading to both the lamp carriage and the lens carriage of such a nature as to cause movement of the lens always in the same direction as the lamp is moved, but with such increased speed ratio with reference to the movement of the lamp as to regulate the focus relation between the lamp and the lens in the same way as the focus relation between the lamp and the parabolic reflector is being regulated by move ment of the lamp with reference to said parabolic reflector. Of course, in stating as above that the lens carriage and lamp carriage have certain specific movements relative to the main reflector, the assumption is that the main reflector is stationary. However, in a broader sense, it does not matter, except for mechanical convenience,

- whether the main reflector is stationary, so long The movement of the lamp with reference to the parabolic reflector to change the focus ,between spot and flood will of course depend upon the shape and size of the parabolic reflector, and similarly, the relative movement of lens with reference to the travelling lamp is determined in any given instance upon the focus characteristics of lens 40. The lamp and lens operating mechanism must simply be such that when the lamp is at spot position with reference to the parabolic reflector, it is likewise at spot position with reference to lens 40, and when the lamp is at full flood position with reference to said reflector, it is also at full flood position with reference to lens 40. Since parabolic reflector 24 is fixed, movement of the lamp to focus between spot and flood is determined by the characteristics of that reflector. To secure corresponding focusing between the lamp and lens 40, said lens must then be moved with reference to the lamp by a proper amount depending upon its own focus characteristics. and it will be evident that the lens will move with reference to the stationary lamp housing in a manner dependent both upon its own focus characteristics, as well as upon movement of the incandescent lamp, and therefore upon the focus characteristics of the parabolic reflector. The operating mechanism for the incandescent lamp and lens is accordingly designed to take these relations into such-account that the light reflected from the parabolic reflector and the light passing through and refracted by condenser or projection lens 40 varies between spot and flood conditions in as nearly as possible exact correspondence as manual focusing member 58 is manipulated.

The drawings show a present preferred form of condenser or projection lens 40. This lens is of the echelon or Fresnel type, its rearward surface 90 being preferably and usually spherical and concave, and its forward surface being provided with a central axial spherical surface SI, and with a series of concentric annular projections or prisms 92 surrounding surface 9|. Each projection or prism 92 is defined by an outer surface 93, which is either torric in shape or else bounded by a surface which is a segment of a cone having its apex on the axis of the lens at a point forwardly of its front face, and a surface 94 which is either cylindric or is a segment of a. cone having its apex on the axis of the lens and to the rear of its rearward face. Lenses of this general type are known in the art, and since the lens per se is not, a part of the present invention, a further detailed description of the lens will not be here required. Suflice it to say that with a lens of the proportions shown, and of an outside diameter of 10 inches, light from an illuminant positioned six and one half inches to the rear of its rearward surface, measured along the axis of the lens, will be refracted by the several prisms of the lens to give spot characteristics to the beam omitted from the lens, while with the illuminant located at a distance of three and one quarter inches from the rearward surface of the lens, the light rays sent out from the lens are uniformly spread out over a wider area to give flood light characteristics. The distribution of light at flood light position with such a lens is quite uniform, while the field covered by the light is comparatively sharply defined. Some leak light is produced, which may be effectively prevented by opaquing lens surfaces 94, as disclosed in an application of Carl R. Ericlmon, flled March 24,

1937, Serial No. 132,803, entitled Echelon condenser lens.

The optical operation of the lamp is as follows: Light rays from filament f of incandescent lamp 30 striking small spherical reflector 49 are reflected back by said mirror and formed into a filament image in the plane of the filament itself. When the lamp is adjusted for spot (Fig. 2), light rays from the filament around mirror 49 and striking parabolic reflector 24 are reflected forwardly and pass around the margins of lens 40 to form a beam of parallel light. Light rays from the fllament and filament image radiated forwardly and passing through lens 40 are refracted and projected likewise as a beam of parallel light, so that the combined light from reflector 24 and projection lens 40 forms a light beam of spot characteristics. n the other hand, assuming the lamp to be adjusted to the flood light position of Fig. 1, light from the filament and radiated rearwardly around small reflector 49 strikes and is reflected by reflector 24 at a wide angle, the outer boundary of the light thrown from the reflector, being, however, comparatively sharply defined. At the same time, light rays travelling forwardly from the filament and filament image and striking projection lens 40 are refracted by said lens at a relatively wide angle, the light from this lens being uniformly distributed and covering mainly the central portion of the field, while the outer boundary of the field is principally lighted from reflector 24. Very little stray or leak light is produced, the boundary of the field lighted by the lamp being quite sharply defined. At the same time, the light distribution from the center of the field to its outer boundary is very uniform. Tests made with a lamp constructed in exact accordance with the present disclosure, having a 24 inch parabolic reflector, a five k. w. incandescent lamp, and having a 10 inch projection lens, when .adjusted to full flood position, have shown an illumination at a 20 foot distant screen of 270 foot candles at the center of the field, and 250 foot candles at the boundary of the field.

Fig. shows a modification of the focusing means for the lamp and lens carriages. As here shown, lamp carriage 3| and lens carriage 42 are provided with downwardly projecting portions I00 and I 0| respectively, which are screwthreadedly engaged by a lead screw member I02 journalled at its ends, as at I03 and I04, in the ends of lower lamp housing portion I8, as shown. The rearward end of lead screw I02 is provided with a manual operating crank I04. Lead screw I02 is provided with a screwthreaded portion I05 of one pitch, and another screwthreaded portion I06 of another pitch. For instance, in a present embodiment of the invention, portion I05 has five threads per inch, while portion I06 has eight threads per inch. Accordingly, the lens carriage and lamp carriage are moved by lead screw I02 in a ratio of eight to five, in focusing between spot and flood conditions.

In the foregoing and in certain of the claims we have specifically spoken of a lamp of the incandescent type. It will be understood, of course, that the present invention is not limited to use of a light source consisting of an incandescent lamp, but that any other light source may be substituted within the scope of the invention and claims.

We have shown and described certain specific illustrative means by which our invention may be carried into efiect; it is to be understood,

however, that various changes in design, structure and. arrangement may be made without departing from the spirit and scope of the present invention or of the appended claims.

We claim:

1. In an incandescent studio lamp, the combination of a lamp housing, a stationary concave reflector disposed within the rearward end of said housing, a light source carriage within said housing adapted to carry a light source along the optical axis of said reflector, a projection lens carriage movable within said housing parallel to said optical axis, a projection lens mounted on said carriage with its center on said optical axis, and focusing means for adjusting said lamp between spot and flood conditions, said means comprising manually operable mechanism for moving the light source carriage between spot and flood positions with reference to the reflector, a pivoted motion multiplying lever arm, an interconnection between the light source carriage and said lever at a point on said lever a given distance from the pivot of the lever, and an interconnection between the lens carriage and the lever at a point on said lever, a predetermined greater distance from the pivot of the lever, whereby the lens carriage is moved through said lever from the light source carriage but at greater speed.

2. In an incandescent studio lamp, the combination of a lamp housing, a stationary concave projecting reflector disposed within the rearward end of said housing, a light source carriage within said housing adapted to carry a light source along the optical axis of said reflector, a projection lens carriage movable within said housing parallel to said optical axis, a projection lens mounted on said carriage with its center on said optical axis, and focusing means for adjusting said lamp between spot and flood conditions, said means comprising manually operable lead screw mechanism engaging said light source and lens carriages and arranged to move said carriages at different speeds relative to said reflector.

3. In an incandescent studio lamp, the combination of a lamp housing, a stationary concave projecting reflector disposed within the rearward end of said housing, a light source carriage within said housing adapted to carry a light source along the optical axis of said reflector, a projection lens carriage movable within said housing parallel to said optical axis, a projection lens mounted on said carriage with its center on said optical axis. and focusing means for adjusting said lamp between spot and flood conditions. said means comprising a manually operable lead screw having on screw portion of one pitch engaging the lens carriage and another screw portion of lower pitch engaging the light source carriage.

4. A studio lamp embodying a lamp housing having an opening in its forward end, a light source mounted in said housing for movement along a line passing through said opening, a condenser lens in the forward portion of said housing in front of said light source positioned with its optical axis on said line of movement and movable forwardly and rearwardly on said axis, said lens being adapted to receive light rays from said light source and to project said rays forwardly from the lamp, a projecting reflector in the housing positioned on said optical axis to the rear of the light source, said reflector being of a diameter greater than that of the condenser lens and being arranged to receive light rays from the light source and to reflect said rays and project them from the lamp housing around said lens, and. means for moving the light source along its line of movement to vary the angle of the light projected by the projecting reflector between spot and flood characteristics, and for concurrently moving the condenser lens along said line of movement in the same direction and at a speed greater than that of the light source to vary correspondingly the angle of the light projected by the condenser lens between spot and flood characteristics.

5. A studio lamp embodying a lamp housing having an opening in its forward end, a light source mounted in said housing for movement along a line passing through said opening, a condenser lens in the forward portion of said housing in front of said light source positioned with its optical axis on said line of movement and movable forwardly and rearwardly on said axis, said lens being adapted to receive light rays from said light source and to project said rays forwardly from the lamp, a small spherical reflector positioned on said optical axis to the rear of said light source and mounted for unitary movement therewith, said reflector being arranged to form an image of the light source in the plane of said light source, a relatively large projecting reflector in the housing positioned on said optical axis to the rear of said small spherical reflector, said projecting reflector being of a diameter greater than that of the condenser lens and being adapted to receive light rays from the light source around said small reflector and to reflect said rays and project them from the lamp housing around said lens, and means for moving the light source and the small spherical reflector along said line of movement to vary the angle of the light projected by the projecting reflector between spot and flood characteristics, and for concurrently moving the condenser lens along said line of movement in the same direction and at a speed greater than that of the light source to vary correspondingly the angle of the light projected by the condenser lens between spot and flood characteristics.

6. In an incandescent studio lamp, the combination of a light source, a condenser lens in front of said light source positioned to refract and project light rays received from said source, and a projecting reflector of a diameter greater than that of the condenser lens arranged in back of said light source and arranged to reflect and project light rays received from said light source around said lens, all symmetrically mounted on a common optical axis, and means for concurrently efiecting relative movement along said axis between the light source and projecting reflector and corresponding relative movement along said axis between the light source and condenser lens in such a manner that the speed of relative movement between condenser lens and projecting reflector is greater than the speed of relative movement between the light source and condenser lens, so as to adjust the angularity of the light projected by the lens and reflector between spot and flood characteristics.

CECIL BARDWELL. CARL R. ERICKSON. JESS C. ROSE.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2481988 *Nov 4, 1944Sep 13, 1949Standard Thomson CorpLight projecting device
US2668904 *Jan 19, 1949Feb 9, 1954Century Lighting IncElectric lighting fixture
US3511985 *Jun 8, 1967May 12, 1970Muscovitch Joseph AAdjustable beam lamp
US4029956 *Mar 24, 1976Jun 14, 1977Alos AgLight fixture for projection device
US4729077 *Mar 10, 1986Mar 1, 1988Mycro Group Co.Variable beam width lighting device
US5207747 *Apr 12, 1991May 4, 1993Musco CorporationMobile lighting system
US6290373Nov 21, 1997Sep 18, 2001Dwight Crane Rentals Ltd.Light fixture with movable bulb carriage
US8960947Mar 4, 2011Feb 24, 2015The Tiffen Company, LlcLighting apparatus
DE1489389B1 *Nov 29, 1963Dec 2, 1971Berkey Technical U H LtdScheinwerfer fuer fernseh und filmstudios zur wahlweisen verwendung als flutlicht oder als punktlichtscheinwerfer
WO2011109673A1 *Mar 4, 2011Sep 9, 2011The Tiffen Company, LlcLighting apparatus
Classifications
U.S. Classification362/277
International ClassificationG03B15/02
Cooperative ClassificationG03B15/02
European ClassificationG03B15/02