Electric lamp and discharge devices – Incandescent lamps
Reexamination Certificate
2002-02-22
2004-08-17
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Incandescent lamps
C313S578000
Reexamination Certificate
active
06777859
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a light source, in particular incandescent lamp, with a bulb, a filament arranged in the bulb, and a heating device for the filament, the filament emitting both visible light and heat radiation.
Light sources of the described type have been known from practice for a long time, and they exist in a large variety of designs and sizes. In this connection, for example, incandescent lamps are known as electrical light sources, in which it is common to bring a tungsten filament by electrical Joule heat to a highest possible temperature. In this process, a temperature radiation is generated. The light yield of incandescent filaments considerably increases as the temperature rises. Besides that, also so-called nonthermal sources of radiation are known, for example, discharge lamps, such as inert gas-, mercury-, sodium-, and metal halide discharge lamps in high-pressure and low-pressure designs.
All so far known, electrically operated types of light sources have the disadvantage that they are very inefficient with respect to converting electric power into visible light output. The conversion barely exceeds 30%. The largest portion of the consumed electric power is an uneconomical dissipation primarily in the form of heat.
A possibility of increasing the efficiency of known light sources consists in that the heat radiated from the filament or glow wire, is reflected from the inner side of the bulb back to the filament or glow wire. As a result, the filament or glow wire undergoes a kind of backheating. This results in that after reaching the same filament temperature, less electric power will be needed than during a heating without reflection. The visible light output, which is transmitted through the bulb, remains in this instance the same. In the ideal case, only that electric power will be needed, which corresponds to the visible, emitted light output and to the thermal dissipation, which is absorbed by the bulb. Thus, the conversion efficiency is improved by the portion of the reflected heat radiation. Theoretically, it would be possible to increase with that the conversion efficiency to as much as 75% or 140 lumens/watt, if one took as a basis the standard thermal dissipation of tungsten lamps of about 25%, and if one neglected the radiation absorption of a mirror coating on the inner side of the bulb. In this connection, for example, dielectric mirror coatings have an absorption of typically 0.1%.
In the case of a mirror coating on the inner side of the bulb with a reflecting power of, for example, 99.9%, statistically, every one thousandth photon in the material of the mirror coating will be absorbed. In the case of a reflection of the radiation into the bulb, the photon flux may therefore undergo only 1000 reflections on the inner side of the bulb, until it is totally absorbed in the bulb. The probability that on its path of reflection, the photon flux strikes the filament or glow wire and is there absorbed, is proportionate to the ratio of the filament volume or the filament surface to the reflecting bulb volume or the reflecting bulb surface.
To achieve a highest possible backheating of the filament, it will therefore be advantageous, when a large filament surface is present, so that the photon flux strikes the filament and is there absorbed after the fewest possible reflections on the inner side of the bulb.
However, in this instance, it is disadvantageous that in the case of an enlarged filament surface, the electrical resistance of the filament becomes smaller, so that for reaching the filament temperature necessary for the light emission, a substantially greater current is needed in the filament than in the case of a normal filament surface or normal filament cross section. This may lead to safety problems for the user of the light source. In summary, there is a dilemma as to a largest possible filament surface and the therefor required and disadvantageous high currents.
It is therefore an object of the present invention to describe a light source of the initially described type, which allows to achieve a high conversion efficiency with simple means and in a reliable manner.
SUMMARY OF THE INVENTION
The foregoing object is achieved by a light source which is designed and constructed such that the heating device includes a heating element for an indirect heating of the filament.
In accordance with the invention, it has been recognized that the development of a separate heating element for the filament accomplishes the foregoing object in a surprisingly simple manner. In this instance, the filament is indirectly heated by the heating element, which offers the great advantage that the filament may be configured irrespective of its electrical resistance behavior. As a result, it is possible to realize a large-surface filament, which exhibits a high absorptive power for heat radiation, which is reflected from the inner side of the bulb. The device, which is needed for heating the filament may be realized independently of the configuration of the filament. Consequently, it is also possible to realize a heating device, which operates with electric currents, which can be safely managed. An electrical contact between the heating device and the filament is no longer needed.
Thus, the light source of the present invention denotes a light source, which allows to achieve a high conversion efficiency with simple means and great reliability.
As regards a most favorable possible absorption behavior for heat radiation, it would be possible to design and construct the filament in the form of a strip, or, quite generally, as a flat filament. As an alternative thereto, one could also make the filament, quite generally, as a volume filament, i.e., a filament, which occupies a spatial volume, or comprises a volume. In particular, one could make the filament in the shape of a cup or cylinder jacket. In this connection, a configuration as a complete cylinder jacket or even as a portion thereof, in particular a cylinder jacket half is possible. In the case of a substantially complete cylinder jacket, such a jacket could also be made open on its side or axially slotted. This is favorable with respect to the thermal expansion behavior of the filament.
To guarantee a particularly effective absorption of the heat radiation being reflected from the inner side of the bulb, the diameter of the cylinder jacket, or of a portion or half thereof, could be only slightly smaller than the diameter of the bulb. In particular in this instance, it would be possible to arrange the filament in the bulb in concentric and/or coaxial relationship with a longitudinal axis of the bulb.
Depending on its configuration, the filament could divide the interior of the bulb into one or more half spaces or subspaces.
The bulb could have such a large outer surface that it is possible to dissipate the surface heat, which is generated, for example, by absorption of heat radiation, with the use of convection cooling or any other forced cooling. The size and form of the filament and the bulb could adapted to each other in a corresponding manner.
Basically, the filament could contain tungsten, and/or rhenium, and/or tantalum, and/or zirconium, and/or niobium. In this connection, adjustments are to be made to the respective needs of the light source characteristics. The filament could contain the last-mentioned materials in a sintered form.
Furthermore, the filament could be composed at least in part of a nonmetal. This could improve the mechanical stability of the filament.
With respect to very high surface temperatures, and very high light currents in the visible range, the filament could be composed at least in part of tantalum carbide, and/or rhenium carbide, and/or niobium carbide, and/or zirconium carbide. This would allow to reach surface temperatures, which are higher than is normal for known tungsten filament lamps.
Concretely, the heating element could be an incandescent element that is heated by the electric current. The filament is heated by the heat radiation of the inca
Alston & Bird LLP
IP2H AG
Zimmerman Glenn
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