ELECTRIC INCANDESCENT LAMP AND BLOWN GLASS BULB THEREFOR

Abstract: The electric incandescent lamp has a blown glass lamp vessel (61) having a neck-shaped wall portion (64), a wall portion (68,68′) curved according to the arc of a circle and extending mainly in the transversal direction and a wall portion (69,69′) curved according to the arc of a circle and extending mainly in the axial direction (62). A filament (71) is arranged near the largest diameter (63). The electric incandescent lamp affords the advantage that it has, independently of its finish (79), a lamp vessel (61) of the same shape and with the same mounting means (72) for the filament (71). The manufacture of incandescent lamps of different kinds is thus considerably facilitated. In the lamp vessel 61, an annular screen (81) can be arranged.

Description: The invention relates to an electric incandescent lamp comprising: - a blown glass lamp vessel sealed in a vacuum-tight manner, provided with . an axis of symmetry . a largest diameter transverse to the axis of symmetry, . a neck-shaped first wall portion behind the largest diameter, the free end of said wall portion carrying a lamp cap having electric contacts, . an internally concave second wall portion, - an internally concave third wall portion, . an internally concave fourth wall portion located opposite the lamp cap in front of the largest diameter, - a helically wound filament arranged about the axis of symmetry substantially in a plane transverse to said axis, - means to keep the filament positioned, - current supply conductors interconnecting the filament and contacts on the lamp cap. The invention also relates to a blown bulb suitable for use in the lamp. A lamp of this type is known from US Patent 2,110,590. In the known lamp the second wall portion together with a reflector arranged within the neck-shaped wall portion constitutes in axial cross-section half an ellipse. The third wall portion is a branch of a parabola which is revolved about an axis parallel to the parabola axis, with the parabola axis being located in between the branch of the parabola and the axis of revolution. The two wall portions are mirror coated and their foci located on a circle coincide and the filament is arranged in the plane through these foci. The known lamp provides a solution to the problem of parabolic reflectors being too narrow in the focal plane if the filament is to be mounted in a deep reflector so as to obtain a satisfactory beam of generated light, and yet avoiding that the transversal dimensions of the lamp exceed a conventional size. As in the known lamp the branches of the parabola are moved apart in a axial cross-section, the lamp vessel in the focalplane is wider. Yet the filament in the focal plane is located in a narrow portion of the lamp vessel, far remote from the largest diameter of the lamp vessel. A drawback of the known lamp therefore is that only filaments consuming a relatively low power can be mounted in the lamp vessel in order to avoid overheating of the lamp vessel. Electric lamps having a power value between 15 and 100 W, for example 15, 25, 40, 60, 75 and 100 W intended to be operated at the mains voltage are manufactured in a large number of types. Not only the finish, the coating or the processing, of the lamp vessel wall, but also its shape and the size and shape of the inner parts of the lamp such as the means to keep the filament positioned are different. The electric incandescent lamps for operation at the mains voltage in the said power range include: - lamps such as those described in the above-cited US Patent 2,110, 590, having a mirror-coated parabolically curved wall portion opposite to which a window is located which, for example is glazed (is slightly light-scattering) for example due to an etching treatment and/or is coloured; - lamps having a substantially spherical lamp bulb which is transparent or is frosted or which is coated with a white or coloured light-­ scattering layer; - lamps having a conical wall portion adjacent to, and a curved wall portion opposite to the neck-shaped wall portion, the conical wall portion being provided with a white or coloured light-scattering layer and the curved wall portion being slightly light-scattering and, as the case may be, being coloured. These lamps emit light on all sides, but supply along the axis in directions remote from the neck-shaped wall portion a higher luminous intensity than in other directions, - lamps having opposite to the neck-shaped wall portion a spherical wall portion which is mirror-coated or is provided, for example with a white light-scattering coating. The manufacture of this large number of lamp types is very complicated due to the variety of lamp vessel types which require on and between the production machinery their own supply and lead-out mechanisms and their own transport means, and which moreover require individual packings. The readjustment of production machines from one lamp type to the other is thus a very laborious operation. Another complication of their manufacture is that the various types of lamps require their own means to keep the filament positioned. It is an object of the invention to provide an electric incandescent lamp having a blown glass lamp vessel shaped in such a way that this lamp vessel may have had a coating or optional processing operation for realising a lamp from a variety of different types. It is also an object of the invention to provide a blown glass lamp bulb suitable for use in such an electric incandescent lamp. According to the invention, in an electric incandescent lamp of the type described in the opening paragraph this object is realised in that - the second wall portion in axial cross-section is substantially curved in accordance with an arc of a circle and extends mainly in the transversal direction between the neck-shaped wall portion and the largest diameter, the centre of curvature being located in front of the largest diameter on the other side of the axis of symmetry, - the third wall portion in the axial cross-section is substantially curved in accordance with an arc of a circle and extends mainly in axial direction in front of the largest diameter, the centre of curvature being located behind the largest diameter and on the other side of the axis of symmetry, said wall portion gradually merging into the second wall portion in the proximity of the largest diameter. - the filament is arranged in the proximity of the largest diameter. Since the second wall portion mainly extends in axial cross-section in the transversal direction, the lamp vessel widens out considerably from the neck-shaped wall portion. This is in great contrast to the lamp of the above-cited US Patent 2,110,590. Even if the lamp has a conventional axial dimension this also results in the possibility of arranging the filament in the proximity of the largest diameter of the lamp vessel and yet positioned deep in the lamp vessel, i.e. relatively close to the neck-shaped wall portion. This has great advantages. For a largest diameter of e.g. approximately 60 mm which is also conventional for commercial lamps using a low power (for example 25 W) filaments having a relatively high power (for example 75 or 100 W) can be incorporated due to their position in the proximity of the largest diameter. In front of the largest diameter the lamp still has a considerable axial dimension so that in mirror coated embodiments the filament is surrounded by mirror coated wall portions over a large spatial angle. The invention will now be described in greater detail with reference to the accompanying drawings which show embodiments of the lamp according to the invention. In the drawings: Figure 1 is a side elevation of a first embodiment of a lamp with the lamp vessel in axial cross-section. Figures 2-5 show a mirror coated blown glass bulb in axial cross-section suitable for use in a second embodiment of the lamp Figure 6 shows a modification of the bulb of Figures 2-5 in axial cross-section. Figure 7 shows partly in side elevation and partly in axial sectional view another embodiment of the lamp. In Figure 1 the electric incandescent lamp has a blown glass lamp vessel 1 which is sealed in a vacuum-tight manner and which has an axis of symmetry 2, a largest diameter 3 transverse to the axis of symmetry and a neck-shaped first wall portion 4 behind the largest diameter 3. The free end of the neck-shaped wall portion 4 carries a lamp cap 5 which has electric contacts 6, 7. The lamp vessel 1 also has an internally concave second wall portion 8, 8′, an internally concave third wall portion 9, 9′, and an internally concave fourth wall portion 10 located opposite the lamp cap 5 in front of the largest diameter 3. A helically wound filament 11 is arranged about the axis of symmetry 2 substantially in a plane transverse to this axis. The lamp has means 12 to keep the filament positioned and current supply conductors 13 which interconnect the filament 11 and contacts 6, 7 on the lamp cap 5. The second wall portion 8, 8′ is curved in axial cross-­ section substantially in accordance with an arc of a circle and extends mainly in the transversal direction between the neck-shaped wall portion 4 and the largest diameter 3. (The Figure shows that the dimensions of the lamp vessel 1 from the neck-shaped wall portion 4 to the largest diameter 3 increase to a greater extent in the transversal direction than in the axial direction). The centre of curvature 14 of the wall portion 8 is located in front of the largest diameter 3 on the other side of the axis of symmetry 2. The mainly transversal direction in which the wall portion 8 extends implies that the centre of curvature 14 is relatively far remote from the largest diameter 3. The third wall portion 9,9′ is an axial cross-section substantially curved in accordance with an arc of a circle and extends substantially in the axial direction in front of the largest diameter 3. (The dimensions of the lamp vessel 1 from the largest diameter 3 increase to a greater extent in the axial direction than they decrease in the transversal direction). The wall portion 9 has a centre of curvature 15 which is located behind the largest diameter 3 on the other side of the axis of symmetry 2. The wall portion 9, 9′ gradually merges in the proximity of the largest diameter 3 into the second wall portion 8, 8′. The filament 11 is arranged in the proximity of the largest diameter 3. In a favourable embodiment the fourth wall portion is curved in axial cross-section in a zone remote from the axis of symmetry substantially in accordance with an arc of a circle, the centre of curvature being located proximate to the axis of symmetry and in front of the filament. This embodiment has the advantage that the lamp may be in the form of a bowl-mirror lamp. In that case the lamp has a reflective coating on the wall portions in front of the filament. Such a lamp may alternatively have, for example a white partly reflective, partly light-transparent coating on said wall portion. Figure 1 shows this shape. The fourth wall portion 10 has an annular zone 16, 16′ remote from the axis of symmetry 2 in which the wall portion in the axial cross-section is substantially curved in accordance with an arc of a circle. The centre of curvature 17 of the zone 16 is located proximate to the axis of symmetry 2 and in front of the filament 11. In the region 18 in the immediate proximity of the axis 2 the fourth wall portion 10 may have a larger radius of curvature, or it may be ogive. In Figure 1 a reflective coating with, for example aluminium, silver, copper/aluminium, gold is denoted by the reference numeral 19. The Figure shows that the filament 11 is at a relatively large distance from the wall of the lamp vessel 1 in all directions. A lamp vessel 1 of the same shape as in Figure 1 may be entirely transparent or substantially frosted. Alternatively this lamp vessel may have a light-scattering coating possibly comprising white or coloured pigment. In a special embodiment this lamp vessel 2 has a white light-scattering coating on the wall portions 4, 8, 8′ and 9, 9′ whilst the wall portion 10 is glazed or has a coating which is not pigmented or is pigmented to a slight extent. In that case the lamp emits more light in the forward direction, in directions which extend at a relatively small angle to the axis 2, than when the entire lamp vessel is provided with the same coating. The lamp has a smaller lateral luminance. In all these embodiments the same stem 12 can be used to keep the filament 11 positioned. It is of special importance that the same means and the same stem can be used to keep the same filament positioned, also when constructing the lamp according to the invention as a reflector lamp. The invention also relates to a blown glass bulb suitable for use in the electric incandescent lamp according to the invention. An important property of the bulb is that it is mechanically strong. The bulb is therefore suitable to be evacuated from manufacturing vacuum lamps or from the manufacture of mirror coatings. In Figures 2-5 identical parts have the same reference numerals as in Figure 1. The lamp vessel 21 is provided with a mirror coating 29 on its inner surface on the wall portions 8, 8′ and 9, 9′ as well as on a part of the wall portion 4. Figure 2 shows the radiation path for light which is emitted by the filament at point 11 in the direction of wall portion 9′ and which is reflected by this wall portion. The wall portion 9′ thus constitutes a screen preventing light from emerging at large angles to the axis 2. The wall portion 9′ reflects the incident light backwards to the wall portion 8 which throws the light in forward directions to the exterior through the wall portion 10 which functions as a light window. It is remarkable that although wall portion 9′ constitutes a screen to the said light rays the wall portion 9 is no hindrance or substantially no hindrance for the emerging rays reflected by wall portion 8. Figure 3 shows that rays thrown onto wall portion 9′ from point 11′ of the filament are also reflected to wall portion 8 and are subsequently thrown to the exterior by this portion 8 without wall portion 9 essentially intercepting rays. It is apparent from Figure 4 that rays thrown onto the wall portion 8′ from point 11 of the filament are reflected and can emerge to the exterior through the light window 10 without any hindrance or any substantial hindrance by the wall portion 9′. Figure 5 also shows that rays which are thrown onto wall portion 8′ by the filament at 11′ are also thrown to the exterior through this wall portion without any hindrance or any substantial hindrance by wall portion 9′. In view of the symmetry of the bulb 21 there is a corresponding radiation path in a lamp from this bulb of light rays which are directly incident on wall portion 8 or on wall portion 9. The mirror-coated wall portion 9, 9′ thus has a multiple function: a) it prevents the emergence of light at large angles to the axis 2, b) it co-operates with the main reflector which is constituted by the wall portion 8, 8′ and c) it is at least substantially no hindrance for rays reflected by this wall portion. The beam components shown in Figure 2-5 are intensified by light which emerges directly without reflection. The mirror coated wall portions 8, 8′ and 9, 9′ surround the filament 11, 11′ in a finished lamp over a spatial angle of approximately 2.5 π sr so that a considerable part of the generated light is concentrated to a beam, also without a reflector body being arranged in the neck-shaped wall portion 4. The filament may be arranged in various shapes, for example substantially as an open circle or along three sides of an isosceles trapezium. In one embodiment of the lamp according to the invention the parabolically curved wall portion has a relief in a zone in the proximity of the neck-shaped wall portion. The wall portion may be roughened, frosted or glazed in this zone. On the other hand, a ripple may be superimposed on the wall portion in the axial cross-section. The amplitude thereof may decrease with an increasing distance to the neck-­ shaped wall portion. Such a relief can homogenize the luminous intensity in the light beam of the lamp in its reflector design. A ripple superimposed on the second wall portion is very attractive because it can be formed on the bulb while blowing it. In Figure 6 the second wall portion 48, 48′ of the bulb 41 has a relief in a zone proximate to the neck-shaped wall portion 4. A ripple 49 having an amplitude decreasing with an increasing distance to the neck-shaped wall portion 4 is superimposed on this wall portion. A lamp which was manufactured from the bulb shown in Figures 2-5 and which has a largest diameter of 60 mm, and consumed a power of 40 W at 225 V, has a filament which was arranged along four sides of an equilateral pentagon. The lamp produced a light beam having a centre value of 550 cd and a beam width of 2×15 °. A commercial reflector lamp of the same power and a largest diameter of 63 mm produces a beam having a centre value of 450 cd at the same beam width. Within the said angle the luminous flux of the lamp according to the invention was 35 % larger than that of the commercial lamp. An electric incandescent lamp also having mirror-coated co-operating wall portions is known from GB 2,097,997. A mirror-coated wall portion widening considerably in the proximity the neck of the lamp vessel is a paraboloid in this lamp. A mirror-coated spherical wall portion is located opposite to it. These two wall portions are connected by an annular wall portion extending in a substantially transversal direction. The known lamp combines the functions which are normally fulfilled by a bowl-mirror lamp together with an external paraboloidal reflector. The spherical reflector throws light on the paraboloidal reflector which has to throw the light to the exterior. The known lamp has a number of drawbacks. The filament is arranged at the largest diameter of the lamp vessel, but it is also surrounded by the spherical wall portion which is located much closer to it. Consequently the lamp can only comprise filaments using a relatively low power. The spherical wall portion throws light on the paraboloidal mirror-coated wall portion but also screens off a considerable part of this wall portion, the more so because the spherical wall portion must be relatively voluminous from a thermal point of view. Finally, due to its shape the known lamp vessel is mechanically relatively weak. In a specific embodiment of the electric incandescent lamp according to the invention, in which the second wall portion and the third wall portion are mirror-coated, an annular screen is arranged inside the lamp vessel and coaxially thereto, this screen being radially surrounded partly by the third wall portion and partly by the fourth wall portion. Such a screen does not or substantially not prevent the passage of the light reflected by a mirror-coated wall portion. On the other hand, this screen prevents that the light emitted directly by the filament without reflection on a mirror-coated wall portion emanates from the lamp vessel at a comparatively large angle to the axis. The screen thus provides for the lamp a higher visual comfort, while the luminous flux in the beam of rays enclosing a small angle with the axis is not or substantially not smaller. The annular screen may be, for example, cylindrical. Alternatively, it is possible that the screen is narrowed towards the fourth wall portion. The screen may be, for example, spherically curved, the point of curvature coinciding with the geometric centre of the filament. Alternatively, the screen may be aspherically curved and may be, for example, ellipsoidal. If such a narrow screen is reflecting, incident light can be reflected to the second mirror-coated wall portion and can be added by this portion to the concentrated light beam. The screen can be supported by the means that hold the filament in position. Another possibility consists in that the screen is supported by springs bearing on the wall of the lamp vessel. In a favourable embodiment, springs cooperate with a portion of reduced width in the neck-shaped first wall portion at the area at which it passes into the second mirror-coated wall portion. Such a portion of reduced width in itself already has the advantage that the surface of the second mirror-coated wall portion is comparatively large due to the fact that this wall portion extends comparatively close to the axis and that nevertheless the neck-shaped wall portion is comparatively wide up to the proximity of the lamp cap. Thus, the lamp satisfies safety requirements, according to which the lamp cap, after being arranged in a lamp holder, cannot be touched with a standarized test finger. Figure 7 shows such a lamp. Parts of the Figure corresponding to parts of Figure 1 have a reference numeral which is 60 higher. The lamp vessel 61 has a part of reduced width 80 at the area at which the first neck-shaped wall portion 64 passes into the second wall portion 68,68′. The second wall portion 68,68′ and the third wall portion 69,69′ have a mirror coating 79. An annular screen 81 is arranged inside the lamp vessel 61 and coaxially thereto, this screen being radially surrounded partly by the third mirror-coated wall portion 69,69′ and partly by the fourth wall portion 70. The screen 81 is supported by resilient wires 82,83, which cooperate with the portion of reduced width 80. An advantage obtained when securing the screen 81 to the lamp vessel 61 is that the screen can be mounted before the process proper of manufacturing the lamp is carried out. The positioning of the screen 81 is simple and accurate. The construction furthermore has a high resistance to shocks. A third spring not visible in the Figure is located in the finished lamp in front of the spring 83. The screen 81 intercepts the light rays a and b and all the rays therebetween, which would otherwise emanate from the lamp vessel, i.e. the ray a and adjacent rays at a comparatively large angle to the axis 62. Due to its spherical shape, the screen reflects incident radiation to the second wall portion 68,68′, which adds this radiation to the beam of rays. The screen may consist of a variety of metals, for example aluminium, chromium-nickel steel, molyndenum and the like.

Claims: 1. An electric incandescent lamp comprising: - a blown glass lamp vessel sealed in a vacuum-tight manner, provided with . an axis of symmetry . a largest diameter transverse to the axis of symmetry, . a neck-shaped first wall portion behind the largest diameter, the free end of said wall portion carrying a lamp cap having electric contacts, . an internally concave second wall portion, - an internally concave third wall portion, . an internally concave fourth wall portion located opposite the lamp cap in front of the largest diameter, - a helically wound filament arranged about the axis of symmetry substantially in a plane transverse to said axis, - means to keep the filament positioned, - current supply conductors interconnecting the filament and contacts on the lamp cap, characterized in that - the second wall portion in axial cross-section is substantially curved in accordance with an arc of a circle and extends mainly in the transversal direction between the neck-shaped wall portion and the largest diameter, the centre of curvature being located in front of the largest diameter on the other side of the axis of symmetry, - the third wall portion in axial cross-section is substantially curved in accordance with an arc of a circle and extends mainly in the axial direction in front of the largest diameter, the centre ofcurvature being located behind the largest diameter and on the other side of the axis of symmetry, said wall portion gradually merging into the second wall portion in the proximity of the largest diameter. - the filament is arranged in the proximity of the largest diameter. 2. An electric incandescent lamp as claimed in Claim 1, characterized in that the fourth wall portion in a zone remote from the axis of symmetry in axial cross-section is substantially curved in accordance with an arc of a circle, the centre of curvature being located proximate to the axis of symmetry and in front of the filament. 3. An electric incandescent lamp as claimed in claim 1, characterized in that the neck-shaped wall portion has a portion of reduced width at the area at which this wall portion passes into the second wall portion. 4. An electric incandescent lamp as claimed in Claim 1 or 3, characterized in that the second wall portion and the third wall portion are mirror-coated. 5. An electric incandescent lamp as claimed in Claim 1 or 4, characterized in that the second wall portion has a relief structure in a zone near the neck-shaped wall portion. 6. An electric incandescent lamp as claimed in Claim 4 or 5, characterized in that an annular screen is arranged inside the lamp vessel and coaxially thereto, this screen being radially surrounded partly by the third wall portion and partly by the fourth wall portion. 7. An electric incandescent lamp as claimed in Claim 6, characterized in that the screen is narrow towards the fourth wall portion. 8. An electric incandescent lamp as claimed in Claim 6 or 7, characterized in that the annular screen is supported by springs bearing on the wall of the lamp vessel. 9. An electric incandescent lamp as claimed in Claim 8, characterized in that the springs cooperate with a portion of reduced width in the neck-shaped wall portion. 10. A blown glass bulb suitable for use in the electric incandescent lamp claimed in any one of the preceding Claims.

Inventors: HOLTEN, PETRUS A. J., ROELEVINK, BAUKE J.
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1988
Main classification: H01K1
IPC codes: H01K1