US 3453481 A
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APPARTUS FOR DEFOCUSING A SEARCHLIGHT Filed July 24. 1967 peer Schimmelpfennig BY Q7/@2mm c? ornevs United States Patent O 3,453,481 APPARATUS FOR DEFOCUSING A SEARCHLIGHT Peter Schimmelpfennig, Wedel, Holstein, Germany, assignor to Licentia Patent-VerwaltungsG.m.b.H., Frankfurt am Main, Germany Filed July 24, 1967, Ser. No. 655,462 priority, applicationlGermany, July 28, 1966,
Inf. c1. Hosb 31/28 Claims U.S. Cl. 314-20 3 Claims ABSTRACT F THE DISCLOSURE Background of the invention The present invention relates to a searchlight comprising a reflector, a high pressure discharge lamp as a light source having its electric arc at the focal point of the reflector as well as apparatus for the defocusing of light.
The shape of the light cone of a searchlight is generally changed by defocusing the light source; that is, by moving the light source which is normally at the focal point of the reflector out of the focal point along the optical axis of the reflector. So moving the light source changes both the angles of incidence and reflection of the light beams with respect to the reflector causing them, in the case of searchlights having normally a highly directional beam, to spread out and illuminate a larger target area.
If the light beam of a searchlight is thus decollimated, the light near to the searchlight additively increases and thus unfavorably decreases the contrast in the illuminated target area. A further disadvantage of axially symmetric decollimation is that the intensity of illumination of the taregt area is made very uneven. There appears in the vicinity of the axis of the light cone a so-called saddle point; that is, the intensity of illumination at small angles at the reflector with respect to the axis is quite .strongly diminished.
Summary of the invention An object of the invention is to produce a searchlight with a high pressure discharge lamp as light source, the light cone of which is so decollimated that only the target area receives substantial illumination.
This and other objects according to the present invention are achieved by placing at least one alternatingv current electromagnet near the high pressure discharge lamp so that the alternating magnetic field is oriented at right angles to the direction of the electric arc.
The influence of a magnetic eld upon an electric arc is well known and has been used for any number of reasons on countless pieces of apparatus. A magnetic field has been commonly used in the past to stabilize the electric arc of a high pressure discharge lamp; there are, in fact, a number of types of apparatus by means of which this can be accomplished.
According to the invention, however, the electric arc of the high pressure discharge lamp is not constrained or stabilized when defocusing is desired but oscillates at the frequency of the alternating magnetic field about the optical axis of the reflector.
The main intensity of radiation of the electric arc of a high pressure discharge lamp emanates from the socalled plasma sphere of the electric arc which, in its rest position, is at the focal point of the reflector and approximates a point-shaped light source. If the plasma sphere is made to oscillate in a prescribed plane around the optical axis of the reflector the light source is apparently enlarged. This enlargement causes the light cone of the Search light to spread out, for example in the horizontal plane, and to avoid the afore-mentioned undesirable increase in light intensity in the area near the searchlight.
Since the light beams of the decollimated light cone originate primarily from the plasma sphere, the defocusing apparatus according to the invention permits the intensity of the light cone to remain approximately constant at the target area. The oscillation of the plasma sphere also naturally causes the radiation of a somewhat more intensive light from the turning points of its locus of motion.
The amplitude of oscillation of the plasma sphere is dependent upon the intensity of the alternating magnetic ield; it can, therefore, be adjusted within certain limits. The plasma sphere is not deflected in a straight line but in the arc of a circle around the cathode so that the distance from the cathode remains constant. The apparent light source thus appears as a slightly curved line of light the length of which is determined by the intensity of the alternating magnetic eld. This phenomenon, it will be noted, advantageously causes a slightly curved beam from the searchlight itself.
Since the decollimation of the cone of light of a searchlight should most conveniently occur in the horizontal plane, two electromagnets are provided in the preferred embodiment of the invention in such configuration that their magnetic field is perpendicular to the horizontal plane as well as the direction of the electric arc.
Brief description of the drawing The single figure is a cross-sectional View of a high pressure discharge lamp, a reflector and a defocusing mechanism according to the preferred embodiment of the present invention.
Description of the preferred embodiment The figure is a cross-sectional view of apparatus according to the preferred embodiment of the invention. The reflector 11 of the searchlight is mounted upon a reilector support 10. Mounted in the middle of the reflector support 10 is a lamp assembly 12, which holds a high pressure discharge lamp 13 in sockets 16 and 17 so that its electric arc will be transverse, e.g., at right angles, to the focal plane of the reflector. Power leads 14 and 15 for the anode and cathode of the electric arc and a small reflector 18 are also included. Two electromagnets 19 and 20 are arranged at right angles to the axis of the high pressure discharge lamp 13 so that their magnetic eld will be at right anlges to the electric arc. The electromagnets 19 and 20 are so designed and situated that they do not interfere with the path of light from the electric arc to the reflector 11. An alternating magnetic field produced by both electromagnets 19 and 20 causes the electric arc, and thus also the plasma sphere, to oscillate about the optical axis of the reflector 11. The resultant apparent enlargement of the light source produces an advantageous spreading of the cone of light from the searchlight.
It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.
1. A searchlight comprising, in combination:
(a) a reilector having an optical axis;
(b) a light source including a high-pressure discharge lamp having an electric arc extending transverse to the focal plane of said reector and situated approxilmately at the `focal point of said reflector; and
(c) defocusing means comprising alternating current electromagnet means situated in the vicinity of said discharge lamp and having an alternating magnetic eld acting at right angles to the discharge path of the electric arc, in consequence of which the arc is oscillated about the optical axis of said reflector and the light beam produced by the scarchlight is defocused.
2. A searchlight as dened in claim 1 wherein said electromagnets means comprise two electromagnets each of whose magnetic telds, in addition to acting at right angles to the discharge path of the electric arc, is at right angles to a given plane.
3. A searchlight as dened in claim 2 wherein said given plane is horizontal.
U.S. Cl. X.R.