US3114855A

US3114855A - Gas discharge lamp with a collimating reflector electrode

Info

Publication number: US3114855A
Application number: US120009A
Authority: US
Inventors: Benjamin A Story
Original assignee: Bausch and Lomb Inc
Current assignee: Bausch and Lomb Inc
Priority date: 1961-06-27
Filing date: 1961-06-27
Publication date: 1963-12-17
Anticipated expiration: 1980-12-17

Description

B. A. STORY GAS DISCHARGE LAMP WITH A CQLLIMATING REFLECTOR ELECTRODE Filed June 2'7, 1961 2 Sheets-Sheet, 1

INVENTOR. BENJAMIN A. STORY I! H" w w:

ATTORNEYQ Patented Dec. 17, 1963 Filed June 27, 1961, Set. No. 120,969 3 Claims. (Cl. 313-113) This invention relates to an electric discharge lamp and more particularly to a compact source lamp having an internal reflector.

Compact source lamps produce relatively high intensity illumination. However, the effective utilization of the illumination is generally dependent upon exterior reflectors. Such reflectors are used to coll-imate and concentrate the light over a relatively small area.

These systems necessarily involve a loss of efliciency. For example a second exterior reflector may be used to direct a portion of the light toward the collimating reflector. For many purposes these systems are satisfactory however, in other cases it is desirable to overcome certain limitations in order to obtain improved characteristics.

In systems capable of providing relatively high intensity illumination such as sun simulator systems, it is desirable to direct a maximum intensity of light toward a collimating I'fiLSCtOT. in order to improve the efliciency of such a system it is desirable to eliminate light losses caused by the light rays passing through the relatively thick quartz envelope. The use of a second exterior reflector causes multiple passes by some of the light rays through the quartz envelope plus undesirable light scattering. In order to reduce these losses and to direct more light toward the collimating reflector, it is desirable to increase the intensity output in a particular region of the lamp ,even though there may be a corresponding drop in total output.

In order to increase the intensity of the light in a preselected quadrant of the lamp it is desirable to have an internal reflector. The use of such a reflector may decrease the overall efliciency of the lamp, however; the resulting increase in intensity in a preselected quadrant more than compensates for the loss in total efliciency. The preselected quadrant defines the portion of the lamp which directs high intensity illumination toward a collimating reflector.

Attempts have been made to coat the inner surface of the quartz envelope with a reflective film. However, the heat in a lamp of this type is relatively great and tends to destroy the reflective coating.

Advantageously a lamp structure according to the invention provides fiavorable performance characteristics. A relatively large percentage of light is concentrated in in the quadrant facing the collimating reflector. The total enregy output of the lamp may be decreased, however, the advantage of increasing the intensity in a preselected quadrant more than compensates for any loss in the total energy output.

The reflectivity of tungsten is poor i.e. about 56% at 2800 centigrade. Also tungsten is a hard brittle material and hard to work. For these reasons it would seem undesirable to incorporate a tungsten reflector. Notwithstanding these problems a smooth reflecting tungsten filament has been incorporated in a novel compact source lamp according to the present invention. :It has been found possible to gather about 22% of the radiant energy with such a reflecting element and to reflect about /2 of this, or about 11% of the total energy, back through the electric arc. This results in increasing the energy output directed toward the collimating reflector.

Briefly the present invention contemplates an electric discharge lamp of the type referred to as a short arc lamp. The lamp comprises a pair of electrodes arranged Within a transmissive envelope. The envelope is filled with a rare gas or a mixture of inert gases such as argon, krypton and xenon either singly or in combination, and can also contain a drop of mercury to provide mercury vapor on heating by the discharge. The pressure of the rare gas should lie above atmospheric pressure. One of the electrodes includes an integral reflector comprising a curved concave surface of revolution. This internal reflector increases the intensity of illumination in a preselected region of the lamp.

The invention will now be described in more detail in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a lamp according to a first embodiment of the invention;

FIG. 2 is a side elevational View in cross section of an anode and a cathode according to the first embodiment of the invention;

FIG. 3 is a side elevational view in cross section illustrating a second embodiment of the invention; and

FIG. 4 is a graphic representation of the polar distribution of the first embodiment of the invention compared with the polar distribution of a conventional lamp.

A compact source lamp according to the first embodiment of the present invention is illustarted in FIGS. 1 and 2. The lamp comprises aquartz envelope 10 which may be formed from some hard glass. A pair of

cylindrical electrodes

12 and 14 are fixed in the envelope and extend through the envelope. The electrodes 12 and '14 are connected through the leads '16 and 1% to a source of electric current 19.

The envelope 1% is tilled with a rare gas, a vapor, or combination thereof, preferably xenon gas plus a drop of mercury. The mercury is vaporized on heating by the discharge. In some cases it may be desirable to use mercury alone and the vapor pressure will therefore be relatively low.

In the preferred embodiment of the invention, the pair of

electrodes

12 and 14 are tungsten and are connected as an anode and a cathode respectively. The electrodes =12 and 14 are arranged in spaced coaxial alignment, wherein, the spacing is relatively small compared with the diameter of the envelope 10. The electrode 12 has a concave curved surface of revolution 20 formed therein and a raised portion 22 which extends upwardly into the area surrounded by the curved surface 20. The curved surface 29 is generally similar to the frustum of a sphere. The portion 22 resembles a plateau which extends upwardly into the frustum.

The curved surface 20 is spherical with an origin at the center of the bright portion of an electric arc. The bright portion of the electric arc is approximately at the tip of the cathode. Generally speaking the origin of the genetrix is placed at about the distance from the apex of the electrode l4 to the portion 22 of the electrode '12. According to the preferred embodiment the origin is approximately /2 to 2 mm. from the apex of the electrode l4; and the radius of curvature is approximately 6 mm. Generally the radius of curvature will be approximately 1.3 times the electrode spacing.

The spherical portion 29 reflects a portion of light through the high intensity portion of the arc, and through a preselected portion of the quartz envelope to thereby increase the intensity in one quadrant of the lamp.

A second embodiment of the invention is illustrated by FIG. 3, wherein a reflecting portion 36) is formed in an electrode 32. The electrode 32 is connected as a cathode by any suitable means 33. The reflecting portion 30 comand has a genetrix prises a spherical surface of revolution with an origin in axial alignment with an axis of the electrode 32. A cone shaped inner portion 34 extends upwardly through the spherical portion 30 and extends beyond the portion 30. The spherical surface has an origin above the apex of the cone shaped portion 34 which lies on the axis of the electrode 32. The origin is approximately the distance from the apex of the cone shaped portion 3 4 to a conventional anode 36.

FIG. 4 illustrates the polar distribution of a lamp according to the first embodiment of the invention compared with a conventional compact source lamp. The polar taxis O180 corresponds to the axis of the electrodes. For comparison purposes the lamps are arranged with their cathode; at the top and correspond to the 0 portion. The center of the electric arc corresponds to the intersection of the 0, 90 and 180 axis. The intensity of the lamp is measured at various points along a meridian curve i.e. at various points equidistant from the center of the lamp in order to indicate the illumination intensity along the polar coordinates. The heavy solid :line indicates the polar distribution of a lamp according to the first embodiment of the invention; and, the relatively light dashed line indicates the distribution of a conventional lamp. These curves are relative polar distribution curves of the respective lamp and do not indicate the total intensity output.

What is claimed is:

1. An electric discharge lamp comprising a transmis sive envelope, a rare gas filling said envelope, and a pair of axially aligned solid electrodes fixed within said envelope, and means electrically connecting said electrodes with the outside of said envelope, a first one of said electrodes including an integral reflector comprising a concave spherical surface generally similar to the frusturn of a sphere and a central raised portion extending upwardly into an area defined by said spherical surface, and a second electrode of said pair of electrodes spaced from said first electrode and having a convex conical shape.

2. An electric discharge lamp comprising a transmissive envelope, a rare gas filling said envelope, and a pair of axially aligned solid electrodes fixed within said envelope in coaxial alignment, means for electrically connecting said electrodes with the outside of said envelope, and a first one of said electrodes including an integral reflector comprising a concave spherical surface of revolution generally similar to a frusturn of a sphere and a central raised portion extending upwardly into an area defined by said spherical surface of revolution, a second electrode of said pair of electrodes having a convex conical shape, said surface of revolution having an origin lying on the axis of said electrodes and between said pair of electrodes at approximately the distmce from an apex of said cone shaped electrode to the raise-d portion of said first electrode.

3. An electric discharge lamp comprising a quartz envelope, a rare gas and a quantity of mercury filling said envelope, a pair of solid electrodes fixed within said envelope in coaxial spaced alignment and means for electrically connecting said electrodes to the outside of said envelope, the spacing between said electrodes being between /2 mm. and 15 mm., a first one of said electrodes including a concave spherical reflecting portion generally similar to a frustum of a sphere and a central raised portion including a relatively fiat top portion extending upwardly into an area defined by said spherical portion, a second one of said electrodes including a convex conical shape on one end thereof, said spherical reflecting portion having a radius of approximately 1.3 times the electrode spacing and an origin on the axis of said electrodes and between said electrodes at approximately the distance from an apex of said cone shaped electrode to the raised portion of said first electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,999,686 De Am-icis Apr. 30, 1935 2,459,516 Francis et al Jan. 18, 1949 2,887,603 Haidinger May 19, 1953 FOREIGN PATENTS 919,962 France Dec. 16, l9'4 6

Claims

1. AN ELECTRIC DISCHARGE LAMP COMPRISING A TRANSMISSIVE ENVELOPE, A RARE GAS FILLING SAID ENVELOPE, AND A PAIR OF AXIALLY ALIGNED SOLID ELECTRODES FIXED WITHIN SAID ENVELOPE, AND MEANS ELECTRICALLY CONNECTING SAID ELECTRODES WITH THE OUTSIDE OF SAID ENVELOPE, A FIRST ONE OF SAID ELECTRODES INCLUDING AN INTEGRAL REFLECTOR COMPRISING A CONCAVE SPHERICAL SURFACE GENERALLY SIMILAR TO THE FRUSTUM OF A SPHERE AND A CENTRAL RAISED PORTION EXTENDING UPWARDLY INTO AN AREA DEFINED BY SAID SPHERICAL SURFACE, AND A SECOND ELECTRODE OF SAID PAIR OF ELECTRODES SPACED FROM SAID FIRST ELECTRODE AND HAVING A CONVEX CONICAL SHAPE.