IE48024B1 - A beacon lamp which emits a conical beam - Google Patents

Abstract

A beacon lamp comprises a substantially point source of light F surrounded by a transparent cap 1 in the form of a solid of revolution defining a first annular lens 5 producing a horizontal disc-shaped beam 6 and a second annular lens 8 producing an upwardly-directed conical beam 9. The lamp is intended to be used by survivors at sea and may be attached to a life jacket.

Description

The invention relates to beacon lights such as are used for indicating the location of survivors at sea of shipwrecks or air crashes, said devices being suitable for equipping life jackets on board aircraft.

Known devices of this type include a substantially point source F of light surrounded by a transparent cap which forms an annular lens suitable for concentrating at least part of the light by the source into a plane perpendicular to a straight line z'z which passes through the source F. The source of light is usually the filament of an incandescent lamp which may be fed with electric current, when required, by an electric cell which may be of a kind which is activated by sea water.

The beam directed by the lens of such a device is visible to an observer placed anywhere in the plane perpendicular to the axis ζ'z which passes through F or in the vicinity of the plane. Since this plane is normally horizontal when the survivor floats on the sea, the lamp allows him to be spotted by ships patrolling in the vicinity. - 48024 Searches for survivors at sea are also made by aircraft. Now, known beacon lamps do not provide significant upward concentration of light or concentrate only a very small part of the rays emitted in a substantially vertical direction. These lamps are therefore practically ineffective for spotting survivors from aircraft.

Preferred embodiments of the invention produce an effective beacon lamp for spotting shipwrecked survivors.

The invention provides a beacon lamp which includes a substantially point source of light F surrounded by a transparent cap wherein the cap forms at least two lenses; a first lens suitable for concentrating part of the light emitted by the source into a first concentrated beam which substantially occupies a diverging nappe or sheet having its apex at the point F; and a second lens suitable for concentrating another part of the light emitted by the source in a second concentrated beam which substantially occupies a plane passing through the point F.

If the lamp is the right way up with a substantially vertical axis z ‘z, light from the light source will be concentrated upwards in a generally conical nappe or sheet of light spreading upwards from the light source. Therefore, if an aircraft passes approximately vertically above the survivor, it will pass twice through regions of concentrated light.

If the half angle a at the apex of the nappe or sheet is the same in all directions about the axis ζ'z the concentrated light beam will occupy the nappe of a right circular cone which is symmetrical about the axis z1z. Otherwise the light may occupy a pyramid shape or an upwardly spreading shape of irregular cross-section.

The invention will be better understood from the description of an embodiment given hereinbelow by way of example, with reference to the accompanying drawing in which the single figure is a partial illustration of a beacon lamp in accordance with the invention for indicating the location of a survivor at sea ,· the figure shows an incandescent light bulb 4 whose filament F constitutes the source of light of the beacon lamp, and a transparent cat 1, which is shown in cross-section.

The cap i is in the form of a solid of revolution whose axis z'z passes through the source F of light of a light bulb 4. In the complete lamp, the cap and the light bulb are fixed on a support and the light bulb is connected to a source of electric current such as a cell which is activated by sea water. When the light bulb 4 is lit, an annular lens 5 formed in the cap 1 concentrates part of the light emitted by the source F into a beam 6 occupying a plane 7 which passes through the source F and which is perpendicular to the axis z'z. A straight line illustrates the plane 7 in the figure. The concentrated beam 6 is substantially uniform in all directions about the axis zz ( although it is not strictly so since the filament F is not a perfect point). In operation it shines in all the directions of the plane 7, whioh is then substantially horizontal.

In accordance with the invention, another lens 8 of the cap 1 concentrates a further part of the light which comes from the source F in a beam 9 into the nappe or sheet of a right circular cone 10 about the axis z'z with an acute, half angle a at its apex (the point F). The concentrated beam 9 - 5 emits light upwards in all directions about the axis z'z . Consequently, any aircraft travelling at such a distance from the axis z'z that the line between the lamp and the aircraft forms an angle of less than a with the axis 2'z will cross the beam twice.

The lens 8 such as illustrated has an inside surface which is conical; i.e. a surface of revolution about the axis z1z with a rectilinear generatrix. The outside surface of the lens 8 is convex and is likewise a surface of revolution about the axis z'z ; its generatrix is a portion of a curve such as an arc of a circle. The shape of these surfaces does not form a part of the invention and can be chosen so as to provide maximum concentration of the beam 9· Further, the invention is not limited to the use of a cap which has circular symmetry nor to obtaining an ascending beam with circular symmetry. If it is considered preferable, the cone about which the ascending beam is concentrated need not be circularly symmetrical. To obtain the advantages of the invention it is necessary only for the generatrices of the cone all to form an acute angle with the vertical axis z'z at the light source, in such a way that an aircraft which passes vertically over the beacon lamp or nearly vertically over it crosses the cone of concentrated light twice. Further, in the lamp in accordance with the invention, the lens 5 may be omitted if air spotting only is required. Alternatively, the cap may have a plurality of lenses by means of which it is possible to obtain several beams concentrated about the generatrices of cones with different acute angles a. An aircraft which passes above the device would then cross each beam twice. This increases the chances of its spotting the survivor.

Claims (3)

1. CLAIMS:1. A beacon lamp which includes a substantially point source of light F surrounded by a transparent cap wherein the cap forms at least two lenses; a first lens 5 suitable for concentrating part of the light emitted by the source into a first concentrated beam which substantially occupies a diverging nappe or sheet having its apex at the point F; and a second lens suitable for concentrating another part of the light emitted by the 10 source in a second concentrated beam which substantially occupies a plane passing through the point F.

2. A lamp according to claim 1, wherein the nappe or sheet is the surface of a right circular cone.

3. A beacon lamp substantially as herein described 15 with reference to and as illustrated in the accompanying drawing.