EP0417835A1

EP0417835A1 - Electric incandescent lamp

Info

Publication number: EP0417835A1
Application number: EP90202354A
Authority: EP
Inventors: Petrus Adrianus Josephus Holten
Original assignee: Philips Gloeilampenfabrieken NV; Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 1989-09-11
Filing date: 1990-09-05
Publication date: 1991-03-20
Also published as: HUT54830A; JPH03101050A; HU203615B

Abstract

The electric incandescent lamp has a lamp vessel (1) with a reflective coating (3). Two similar filaments (4, 5) connected electrically in parallel together constitute a polygon and are arranged at the mirror image places one of the other in a plane (19) transverse to the axis (2) of the lamp vessel. The lamp emits a symmetrical light beam having a high intensity at the centre thereof.

Description

The invention relates to an electric incandescent lamp to be operated at mains voltage comprising:
. a translucent lamp vessel with an axis, which is provided with a reflective coating,
. a first and a second wound filament having end portions, which are arranged in the lamp vessel near the axis thereof,
. which filaments are connected at their end portions to current supply conductors emanating from the lamp vessel and are arranged electrically in parallel.
Such a lamp is known from NL 121 505.
In the known lamp, the filaments are arranged linearly at an angle of 45° to the axis and at right angles or parallel to each other.
This shape and this arrangement result in that portions of the filaments are located at a great distance from the axis of the lamp vessel. This has the consequence that the light beam formed by the reflective coating of the lamp vessel has a large width and hence a low luminous intensity at the centre. Another consequence is that the light beam is inhomogeneous and not rotation-symmetrical. The filaments may have different powers, for example one twice that of the other.
Various other incandescent lamps having several parallel-connected filaments are known. For example, EP 0280475-A discloses a lamp having two transversely arranged filaments constituting a closed figure. One of these filaments is designed for a longer life than the other. Thus, it is achieved that the lamp continues to emit light for a long time when a first filament has already burnt through. Such a lamp is not efficient because the longer life of the filament having the longest life is inevitably coupled with a low light output per unit energy consumed. The net light emission of the filament having the longest life is lower than the gross light emission thereof because due to evaporation of the material of the filament having the shortest life after it has burnt through, an absorbing deposit of evaporated filament material has formed on the lamp vessel.
A similar lamp is known from GB 426477.
In incandescent lamps having a reflective coating, the filament is mostly arranged transversely so as to be bent around the axis of the filament. Such a filament is known from US 4,777,300. Due to the comparatively great length of an incandescent filament to be operated at mains voltage, this filament extends, also when it is arranged so as to be bent around the axis, at a comparatively great distance from the axis. This results in a comparatively large width of the light beam formed. Other consequences of the position and the shape of the filament are the formation of a non-symmetrical beam and a comparatively low luminous intensity at the centre thereof.
The invention has inter alia for its object to provide a lamp of the kind described in the opening paragraph, which has a more symmetrical light beam having a high luminous intensity at the centre of the beam.
According to the invention, this object is achieved in that
- the first and the second filament are similar and together constitute a polygon,
- are supported between their end portions by supporting members and
- are arranged mainly at the mirror image places one of the other and mainly transversely to the axis.
Due to the arrangement of the filaments, light is generated around the axis of the lamp vessel and a light beam of high symmetry and high luminous intensity is obtained at the centre thereof.
With a given power consumption, for example 60 W, the filaments each have a smaller length than one filament having this power, for example with a lamp for 220 V 19 mm instead of 24 mm. As a result, the filaments are located closer to the axis of the lamp vessel than with a lamp having only one filament.
A conventional filament having the form of a trapezium open at its base extends at a greater distance from the axis than the filaments of a lamp according to the invention when they constitute, shaped and arranged in a corresponding manner, together a regular hexagon. Both their maximum distance and their average distance are only 80% of that of the conventional filament. Thus, a narrow light bear and a high luminous intensity at the centre thereof are obtained. The luminous intensity of the beam is more than 20% higher.
For the sake of the symmetry of the light beam, the lamp has filaments which are similar, that is to say that they have the same specification, such as length and wire thickness. Nevertheless, filaments having the same specification, even of the same lot, may have unequal properties, especially unequal lives. This may be due, for example, to an error in the filament wire, as a result of which this wire is locally thinner. This results in a shorter life. In a lamp having a first and a second filament, in an extreme case one filament could burn through after 700 hours, while the other filament can continue to emit light for 300 further hours.
In an embodiment of the incandescent lamp according to the invention, a measure is taken by which the second filament burns through a very short time after the first filament, also if the first filament burns through very early. In this embodiment, corresponding supporting members of the first and the second filament are electrically connected to each other.
Embodiments of the incandescent lamp according to the invention are shown in the drawing. In the drawing:

Fig. 1 is a side elevation of an embodiment with a lamp vessel partly broken away,
Fig. 2 shows the filaments of Fig. 1, viewed along the axis of the lamp vessel,
Fig. 3 shows the electric equivalent circuit diagram of the lamp of Fig. 1,
Fig. 4 shows this equivalent circuit diagram after a filament has burnt through,
Fig. 5 is a side elevation of a second embodiment.

In Fig. 1, the electric incandescent lamp to be operated at mains voltage has a translucent lamp vessel 1 with an axis 2. The lamp vessel is provided with a reflective coating 3, for example a layer of aluminium applied by vapour deposition.
A first and a second wound filament 4 and 5, respectively, (see also Fig. 2) having end portions 6, 7 and 8, 9, respectively, are arranged in the lamp vessel 1 near the axis 2 thereof. They are connected at their end portions 6, 7 and 8, 9, respectively, to current supply conductors 10, 11, which emanate from the lamp vessel. The filaments are connected electrically in parallel.
The lamp shown has an Edison lamp cap 12 provided with contacts 13, 14, to which a respective current supply conductor 10, 11 is connected.
In the embodiment shown, the mirror-coated part of the lamp vessel 1 is parabolic; this part could have been shaped differently, for example in the form of an ellipse, or by rotating a curve, for example a branch of a parabola or an arc of a circle, about the axis 2.
The filaments 4, 5 (see also Fig. 2) are similar and together constitute a polygon, in the drawing a hexagon. They are supported between their end portions 6, 7 and 8, 9, respectively, by supporting members 15, 16 and 17, 18, respectively, which are anchored in an insulator body 20.
The filaments 4, 5 are arranged in the lamp vessel 1 mainly at the mirror image places one of the other and mainly in a plane 19 transverse to the axis 2. In the embodiment shown having a parabolic lamp vessel 1, the focus of the paraboloid lies in the plane 19 on the axis 2.
Corresponding supporting members 15, 17 and 16, 18, respectively, of the first and the second filament are interconnected pairwise.
In Fig. 3, the filament 4 of Fig. 2 is represented in the form of three series-connected equal resistors 40-42. Likewise, the filament 5 is represented in the form of series-connected resistors 50-52 having the same value R also equal to that of 40-42. When a voltage of u V is applied between the conductors 10, 11, there is a voltage of 1/3 u V across the resistor 40.
When the resistor 50 has become infinitely large, due to the fact that the filament part represented thereby has burnt through (Fig. 4), the voltage across the resistor 40 is higher. The equivalent resistance of the resistors 41 and 51 and of 42 and 52 is each time 1/2 R. The overall resistance between the conductors 10 and 11 is therefore R + 2 x 1/2 R = 2R. The voltage across the resistor 40 has therefore increased from 2/6 u V to 3/6 u V, that is to say by 50% of the original voltage. At an overvoltage of 50%, a filament 4 has a life which is 0.35% of the nominal life. When the filament 5 having a usual nominal life of 1000 hours burns through prematurely after 700 hours, at the nominal voltage 300 operating hours are still left for the filament 5. Due to the measure taken, these remaining operating hours are reduced to 0.35% thereof, i.e. to about 1 hour. A lamp having a high light quality can thus not continue to burn as an ordinary lamp of low power and low light quality for a long time.
If each filament has only one supporting member, the overvoltage in a part of the filament burning for the longest time is 33.33% and the remaining life is reduced to 1.8%.
If the filaments each have three supporting members, the overvoltage in a part of the filament having the longest life is 60% and the remaining life is reduced still further than in the case shown in the drawing. However, it should be noted that a larger number of supportini members reduces the efficiency of the lamp due to heat losses. A smaller number of supporting members favourably influences the efficiency of the lamp, but unfavourably influences the luminous flux in the light beam due to the fact that the filaments are arranged farther from the axis of the lamp vessel. In general, one or two supporting members per filament are therefore chosen.
In Fig. 5, parts corresponding to parts of Fig. 1 have a reference numeral which is 20 higher. The filaments 24, 25 lie in the plane 39 transverse to the axis 22 coinciding with the largest diameter of the lamp vessel 21. The lamp shown is a bowl mirror lamp intended to be used in ar external parabolic reflector. The lamp vessel 21 for this purpose has a reflective coating 23 on the surface remote from the lamp cap 32, which is curved along an arc of a circle, whose centre of curvature 23′ is located on the other side of the axis 22 and of the plane 39 in which the filaments are positioned. The filaments 24, 25 and the supporting members 37, 38 have the geometry of Fig. 2.

Claims

1. An electric incandescent lamp to be operated at mains voltage comprising:
. a translucent lamp vessel with an axis, which is provided with a reflective coating,
. a first and a second wound filament having end portions, which are arranged in the lamp vessel near the axis thereof,
. which filaments are connected at their end portions to current supply conductors emanating from the lamp vessel and are arranged electrically in parallel,
characterized in that
. the first and the second filament are similar and together constitute a polygon,
. are supported between their end portions by supporting members and
. are arranged mainly at the mirror image places one of the other and mainly transversely to the axis.

2. An electric incandescent lamp as claimed in Claim 1, characterized in that corresponding supporting members of the first and the second filament are electrically connected to each other.