Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Reexamination Certificate
2000-11-14
2003-06-24
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
C313S635000
Reexamination Certificate
active
06583564
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a discharge lamp for a headlight, more particularly to the shapes of light-intercepting films included in a lamp.
BACKGROUND OF THE INVENTION
When a discharge lamp is used as a light source for a vehicle headlight or for a liquid crystal projector, it is combined with a reflecting mirror. In recent years, to prevent a reflecting mirror from being deteriorated by ultraviolet rays radiated from a discharge lamp, a discharge lamp including ultraviolet-cutting glass as an outer tube has been used widely.
In general, to realize a proper light distribution by combining a reflecting mirror and a discharge lamp, it is required to control the position of a luminous portion, namely, an arc, with respect to the reflecting mirror with extremely high precision.
However, because the light distribution of an arc, which is a luminous portion of a discharge lamp, is influenced by such factors as the shape of an arc tube, internal pressure, lamp voltage, tube current, etc., it is difficult to control it mechanically in the same way as a filament used in a bulb, etc. Thus, it has been proposed to obtain an accurate light distribution by intercepting optically a part of the arc, which is difficult to control for its position, by forming a light-intercepting film on an outer tube.
JP-9-500489A proposes a discharge lamp including an arc tube enclosed by an outer tube. In the discharge lamp, external lead wires extend from respective electrodes to respective contact points to a base. A neck portion of the arc tube is fixed into the base, and a power supply line for one external lead wire extends along the external surface of the outer tube.
On the outer tube, a light-intercepting film extends on the side close to the base, from the position making an angle &agr; of 50 degrees with a line perpendicular to the outer tube at the center region between the electrodes, to the position making an angle &bgr; of 65 degrees with the same line. Furthermore, on the outer tube, two band-shaped light-intercepting films extend in parallel with the outer tube, and the two band-shaped light-intercepting films face apart from each other. The two band-shaped light-intercepting films have respective edges making an angle &ggr; of 165 degrees with respect to the circumference of the outer tube, and respective edges facing with each other and making an angle &dgr; of between 85 degrees and 145 degrees.
FIG. 11A
illustrates a configuration of a headlight using the conventional discharge lamp. A discharge lamp
40
includes an arc tube
42
enclosed by an outer tube
41
, and is arranged within a mirror
45
having a front glass
44
mounted at its opening. A light-intercepting film
46
a
extends on the side close to a base
43
of the outer tube
41
, and two band-shaped light-intercepting films
46
b
(only a film on one side is shown) extend in parallel with the axial direction of the outer tube
41
.
As shown by the arrows “a”, light radiated from the arc tube
42
is reflected by the mirror
45
, and passes through the front glass
44
to illuminate forward.
FIG. 11B
shows a light distribution pattern. A region
48
is a region illuminated by light passing through the front glass
44
.
A region
50
indicated by a dot pattern shows a region where light passing through the front glass
44
does not reach. The boundary between the regions
48
and
50
is a cutline
49
. To form such a light distribution pattern, unwanted light is cut from light radiated from,the arc tube
42
by the light-intercepting films
46
a
and
46
b
and sections
47
a
,
47
b
of a light-intercepting plate
47
.
Viewing the light distribution pattern in the up-and-down direction, the illuminated region indicated by
48
a
in
FIG. 11B
is wider than the illuminated region indicated by
48
b
. When a discharge lamp forming such a light distribution pattern is used for a vehicle, both sides of driving lane and opposing lane can be illuminated. For example, in the case of left-hand traffic, because the region
48
b
on the side of opposing lane is cut for its upper illuminated region compared to the region
48
a
on the side of driving lane, blinding of oncoming vehicles can be prevented.
In such a conventional discharge lamp, although generation of glare resulting from unwanted light in the direction to pass through these light-intercepting films can be inhibited by the light-intercepting film
46
a
on the side close to the base
43
and the two band-shaped light-intercepting films
46
b
, it has not been able to avoid glare resulting from unwanted light passing through a portion where no light-intercepting film is formed, particularly a portion far from the base
43
.
For example, unwanted light (arrows “b” and “c”) radiated from the arc tube
42
and reflected by the end on the side far from the base
43
(particularly, at the corners of the end of the outer tube
41
) is reflected by the mirror
45
, and passes through the front glass
44
to illuminate forward. Such light is unwanted to form the light distribution pattern as shown in
FIG. 11B
, and it will illuminate the region
50
that does not need to be illuminated, or will illuminate the region
48
that has been illuminated by the necessary light indicated by the arrows “a” over again. Thus, unevenness is generated in the intensity distribution of the light distribution pattern, resulting in the generation of glare.
To prevent such generation of glare, it is necessary to intercept unwanted light trying to enter the front glass
44
by providing a light-intercepting plate separately. Thus, increased structural complexity and increased weight of a lighting fixture have not been able to be avoided.
The present invention solves the above-mentioned conventional problem. It is an object of the present invention to provide a discharge lamp further including a light-intercepting film extending in a portion far from the base, so that glare can be reduced, and a lighting fixture can be simplified and reduced in weight.
SUMMARY OF THE INVENTION
In order to accomplish the above object, the present invention provides a first discharge lamp including: an arc tube having a discharge space in which a pair of electrodes having tips facing with each other are arranged; an outer tube enclosing the arc tube; a base that fixes one side of the outer tube; and two band-shaped light-intercepting films extending on a surface of the outer tube in the direction of the axis of the arc tube and in parallel with each other, the two band-shaped light-intercepting films having at least a portion overlapping both ends of the discharge space when viewing the outer tube in the direction perpendicular to the axis of the arc tube, wherein:
when the tip within the discharge space of the electrode on the side of the top of the outer tube between the pair of the electrodes is determined as a basis position, in at least one of the two band-shaped light-intercepting films, an extending portion is formed that is on the side of the top of the outer tube with respect to the basis position and extends in the circumferential direction of the outer tube. According to such a discharge lamp, reflected light from the end of the outer tube on the side far from the base can be cut, and unwanted light can be cut more reliably. Thus, unevenness in the intensity distribution of the light distribution pattern can be reduced, and generation of glare can be prevented. Furthermore, because glare can be reduced by the lamp itself, it is not necessary to intercept unwanted light by providing a light-intercepting plate separately, and it is not necessary to add a further mechanism for reducing glare such as a light-intercepting plate, so that a lighting fixture can be simplified and reduced in weight.
It is preferable that a power supply line further is arranged so as to face the side face of the outer tube, and the extending portion is formed so as to extend toward the side opposite to the side on which the power supply line and the outer tube face each other.
It is preferable that wh
Kiryu Hideaki
Murase Takayuki
Patel Ashok
Zimmerman Glenn
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