Electric lamp and discharge devices – With optical device or special ray transmissive envelope – Reflector
Reexamination Certificate
2000-09-27
2003-05-27
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With optical device or special ray transmissive envelope
Reflector
C313S112000, C313S493000, C313S635000
Reexamination Certificate
active
06570302
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electric lamp comprising a light-transmitting lamp vessel wherein a light source is arranged,
said electric lamp comprising a light-absorbing medium, and
at least a part of the lamp vessel being provided with an interference film.
Such lamps are predominantly used for general illumination purposes, for example as efficient replacements for incandescent lamps. Said electric lamps are further used in so-called sign and contour illumination, signal illumination such as in traffic lights, and projection illumination and fiber optics illumination. Such electric lamps are also used for automotive applications, for example as headlamps or indicator lamps in vehicles, for example as an amber-colored light source in indicators or as red-colored light source in brake lights of automobiles. Alternative embodiments of such lamps, wherein the color temperature is increased by means of a light-absorbing coating, can also be used as a headlamp of a vehicle.
An electric lamp of the type mentioned in the opening paragraph is known from DE-GM 86 00 640. In the known electric lamp, an interference film reflecting blue light is provided on the lamp vessel of a halogen incandescent lamp for use in automobiles, and a light-absorbing medium is provided on an opaque part of the inner surface of the lamp vessel.
A drawback of lamps comprising a light-absorbing medium provided on an opaque part of the inner surface of the lamp vessel is that the effectiveness of the light-absorbing medium is relatively small.
It is an object of the invention to provide an electric lamp of the type described in the opening paragraph, wherein said drawback is obviated.
In accordance with the invention, the electric lamp of the type described in the opening paragraph is characterized in that light originating from the light source reaches the interference film mainly via the light-absorbing medium.
In the known lamp, light generated in the lamp vessel is only absorbed by the light-absorbing medium if the light generated is (accidentally) directed such that it is incident on the light-absorbing medium. Since, in the known lamp, the light-absorbing medium is provided only on a relatively small surface in the lamp vessel, namely the opaque part of the inner surface of the lamp vessel, the light-absorbing effect of the light-absorbing medium is relatively small. After all, the major part of the inner surface of the lamp vessel is light-transmitting. Light which is reflected by the interference film often reaches the light-absorbing medium only after multiple reflections. Consequently, there is only a relatively small chance that the reflected light ultimately reaches the light-absorbing medium and that said reflected light is absorbed in said light-absorbing medium. As a result, a substantial part of the reflected light is still emitted by the state-of-the-art electric lamp, which substantially reduces the intended effect of the interference film. The effectiveness of the absorption by the light-absorbing medium is considerably increased by providing the light-absorbing medium, in accordance with the measure of the invention, in such a manner that light originating from the light source reaches the interference film via the light-absorbing medium.
The light-absorbing medium can be provided in the electric lamp in different ways.
An embodiment of the electric lamp in accordance with the invention is characterized in that a wall of the lamp vessel comprises the light-absorbing medium.
Light-absorbing media can be readily incorporated in the wall of the lamp vessel which is made, for example, of glass, such as quartz glass or hard glass, or of a translucent ceramic. In this embodiment, the interference film is preferably applied directly to a side of the wall of the lamp vessel which faces away from the light source. Since the light-absorbing medium is provided in the wall of the lamp vessel and the interference film, light reflected by the interference film passes through the light-absorbing medium twice, which leads to a further improvement of the effectiveness of the absorption process. In addition, light which is reflected to and fro between the interference film on both sides of the lamp vessel passes through the light-absorbing medium twice at every reflection.
An alternative embodiment of an electric lamp in accordance with the invention is characterized in that the light-absorbing medium comprises a light-absorbing layer which is situated between the lamp vessel and the interference film.
Since the light-absorbing medium is provided between the outside surface of the lamp vessel and the interference film, light reflected by the interference film passes through the light-absorbing medium twice, which causes the effectiveness of the absorption process to be further improved. In addition, light which is reflected to and fro between the interference film on both sides of the lamp vessel, passes through the light-absorbing layer twice at every reflection.
In the known lamp, a light-absorbing medium in the form of a light-absorbing layer is applied to an inner surface of the lamp vessel, the light-absorbing layer being exposed to the halogen atmosphere in the lamp vessel. Under the influence of this relatively aggressive atmosphere, the light-absorbing layer is damaged, leading to a further reduction of the effectiveness of said light-absorbing layer. It is also possible that parts of the light-absorbing layer become detached from their base and end up in the atmosphere of the lamp vessel. Such detached parts may adversely affect the lamp atmosphere in the lamp vessel, for example the so-called tungsten cycle. In addition, deposits on a light-transmitting part of the inner surface of the lamp vessel (blackening) cause the efficiency of the lamp to decrease. By applying the light-absorbing layer at a side of the wall of the lamp vessel which faces away from the light source, the influence of the light-absorbing medium on the atmosphere in the lamp vessel is annihilated.
In an alternative embodiment of an electric lamp, the light-absorbing medium is provided on an inner surface of the lamp vessel.
The light-absorbing properties of the light-absorbing medium provided in accordance with the measure of the invention are improved, in particular, if the interference film reflects in a wavelength range wherein the light-absorbing medium absorbs. A favorable embodiment of the electric lamp in accordance with the invention is characterized in that the interference film reflects predominantly in a wavelength range wherein the light-absorbing medium absorbs.
The synergistic effect obtained by this measure resides in that the reflective power of the interference film is tailored to meet the absorbing properties of the light-absorbing medium. The light which originates from the light source and wants to issue to the exterior through the lamp vessel is partly absorbed by the light-absorbing medium, whereby the magnitude of the part absorbed depends upon the thickness of the light-absorbing medium and the effectiveness of the absorption process. Part of the light which is allowed to pass by the light-absorbing medium, however, has a wavelength in the wavelength range which should be absorbed by the light-absorbing medium. As a result of the fact that, in accordance with said embodiment of the invention, the interference film is designed so that, in particular, this light which has been allowed to pass is reflected, this reflected light again passes through the light-absorbing medium so that a further part of this light is absorbed. In such cases, after having passed through the light-absorbing medium twice, part of the light, which is absorbed by the light-absorbing medium, will still be present in the lamp vessel. This light will try to leave the lamp vessel at a different location (for example at the opposite side of the lamp vessel). At this other location, said remaining part of the light will again meet a barrier in the form of a light-absorbing medium in combination with an interf
Boonekamp Erik Paul
Hebbinghaus Gerhard
Van Rijswick Mathias Hubertus Johannes
Van Sprang Hendrik Adrianus
Keegan Frank
Koninklijke Philips Electronics , N.V.
Quarterman Kevin
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