GB2036942A - Navigation beacon with a high light output - Google Patents

Abstract

An optical device for assisting in the guidance of aircraft on airport runways, comprises a light source S and two coaxial globes 2, 3. The inner globe 2 has prism assemblies along generators of its inner surface and along horizontal annuli of its outer surface, and the outer globe 3 has prism assemblies along generators of its inner surface and has a smooth outer surface. Light from the source S is concentrated in azimuthal directions by the inner surface prisms and in an elevational direction by the outer surface prisms. The smooth outer surface of globe 3 allows easy maintenance. The inner surfaces of the domes of the globes may be provided with annular prisms 25, 33 to provide light in all azimuthal directions. The inner globe may comprise two half-globes of different colours. <IMAGE>

Description

SPECIFICATION Optical device with a high light output The present invention relates to an optical device with a high light output intended especially to be used as a luminous beacon for a visual aid to navigation.

For an optical device to produce a light beam having the strongest light intensity in the useful zone without having to increase its overall size and the power of the light source, it is indispensable to provide means to prevent or reduce light losses and to concentrate the maximum of omnidirectional light rays from the source in the angle of the useful beam. In the special case of light beacon devices, concentration of the light rays must be effected so that the useful beam has a minimal width in azimuth and in elevation combined with a minimal light intensity for welldefined visual ranges. The standards which must be satisfied by a luminous beacon device are specified in the International Civil Aviation Convention.

An optical beacon device having means to concentrate the light beam in azimuth and in elevation is known. This device comprises a globe of transparent material with assemblies of prisms distributed over its inner lateral surface and an assembly of horizontal annular prisms on its outer lateral surface. The effect of the prisms distributed over the inner surface is to concentrate the light rays in an aperture angle in azimuth and the effect of the horizontal annular prisms distributed over the outer surface is to concentrate the light rays in an aperture angle in elevation.

This device has two major disadvantages: 1. Since the outer surface is not smooth, it is difficult to maintain, which is prejudicial to the maintenance of the performance of the device.

2. The prisms formed on the inner surface effectively deflect only a part of the light rays which they receive from the source. This disadvantage is illustrated by the drawing of Figure 1 which shows at 1 a part of the globe in horizontal section. S represents the light source.

The direction SA represents the axis of one.of the two outgoing light beams and the broken lines represent paths of three light rays emitted by the source S and reaching the globe on the faces of the prism XYZ.

The light rays included in the angle XSY reach the useful face XY of the prism XYZ and are refracted in the useful direction required. On the other hand, the light rays included in the angle YSZ are captured by the reverse face YZ of the prism XYZ and are not useful for the outgoing beam in question. The "geometrical efficiency" of a prism XYZ, expressed by the ratio of angle XSY to angle XSZ, decreases much more rapidly than the deflection which the globe causes the light rays originating from the source S to undergo increases. This decrease of efficiency is such that it becomes practically useless to provide prisms beyond an angle of approximately 600 on either side of the axis SA of each outgoing light beam.

An object of the invention is to provide an optical device having a substantially improved light output which, for a smaller consumption of energy and a reduced overall size, enables it to produce a light beam which satisfies the standards laid down for visual aids to navigation by the International Civil Aviation Convention.

A further object of the invention is to provide an optical device of high light output and easy maintenance, suitable especially for the guidance of aircraft.

According to the invention there is provided an optical device comprising a light source and a globe of transparent material whose outer lateral surface is formed with assemblies of horizontal annular prisms and whose inner lateral surface is formed with assemblies of prisms extending along the generating line of the inner lateral surface, characterised in that it has a second globe of transparent material outside of the coaxial with the first globe, the outer surface of this second globe being smooth and the inner lateral surface being formed with assemblies of prisms extending along the generating line of the inner lateral surface. In a preferred embodiment the domes of the globes can additionally have annular prisms on their inner surfaces. In another embodiment the angles of intersection of the prisms formed on the inner surface of the globes are advantageously rounded.

A description of an optical device according to a preferred embodiment of the invention is given hereinafter with reference to the accompanying drawings wherein: Figure 1 is an explanatory sketch illustrating the limits of useful deflection of the light rays in a known device; Figure 2 is a vertical section of an embodiment of the device according to the invention; Figure 3 is a horizontal section along the line Ill-Ill of Figure 2; Figure 4 is vertical section of an alternative form of the embodiment of Figure 2.

The invention will be described in its application to an aerodrome runway margin beacon. The purpose of these beacons is to produce on each side of the runway light beams which are practically parallel to the axis of the runway in the two directions of travel, the beams having specific aperture angles in azimuth and in elevation. Each beacon produces two beams whose axes have an angular offset corresponding to the convergence laid down for the light beacon.

Referring to Figures 2 and 3, it will be seen that the device 1 according to the invention comprises, surrounding a light source S concentricaliy, two globes 2 and 3 of any transparent material desired, fixed to a base (not shown) by any means desired. The axes SA and SA' represent the axes of the two useful light beams.

The inner globe 2 has on its inner lateral surface two assemblies of prisms 21,22 visible in Figure 3, which extend along the generating line of the inner lateral surface on either side of the axes SA and SA' of the beams. In the embodiment described the axes SA and SA' have an angular offset 3.50 to one side, namely, that on which the runway to be lighted is to bye situated, so as to ensure the required convergence of the light beams towards the runway, as mentioned above.

The function of these assemblies of prisms is to deflect a first time the light rays emitted by the source towards the axes SA and SA' of the beams. The outer lateral surface has horizontal annular prisms 23, 24 whose function is to concentrate the light energy in the prescribed aperture angle in elevation.

The outer surface 34 of the outer globe 3 is smooth to ensure easy maintenance. The inner lateral surface has at least two assemblies of prisms 31, 32 as shown in Figure 3, which extend along the generating line of the lateral surface.

Like the assemblies of prisms 21, 22 of the inner globe, the assemblies of prisms 31, 32 have an angular offset to ensure the required convergence of the beams. The function of the assemblies of prisms 31, 32 is to concentrate the light rays, already tilted by the prisms 21, 22, in the prescribed aperture angle in azimuth for each of the light beams. The increase obtained in the light output enables the device according to the invention to comply with the light intensity diagram laid down by the standards of the International Civil Aviation Convention by using a light source of a power lower than the power necessary in known devices and while having a lower overall size. The angles of intersection of the inner prisms are advantageously rounded so as to diffuse the lost rays.

To serve simultaneously as a guide beacon, the device according to the invention is provided with horizontal annular prisms formed on the inner surface of the domes of the globes 2 and 3. Figure 4 shows a vertical section of such an embodiment wherein the prisms 25 can be seen on the inner surface of the dome of the globe 2 and the prisms 33 on the inner surface of the dome of the globe 3. The effect of these prisms is to concentrate the light energy not used by the prisms of the lateral surfaces into the aperture angle in elevation so as to make the beacon visible in all azimuthal directions during runway approach manoeuvres.

The inner globe 2 can be realised with two halfglobes of different colours, enabling the optical device according to the invention to be used to obtain two beams of different colours in the directions SA and SA', when this is required.

Claims (4)

1. An optical device comprising a light source and a globe of transparent material whose outer lateral surface is formed with assemblies of horizontal annular prisms and whose inner lateral surface is formed with assemblies of prisms extending along the generating line of the inner lateral surface, characterised in that it has a second globe of transparent material outside of and coaxial with the first globe, the outer surface of this second globe being smooth and the inner lateral surface being formed with assemblies of prisms extending along the generating line of the inner lateral surface.

2. An optical device according to claim 1, characterised in that the inner surface of the domes of the globes is formed with horizontal annular prisms.

3. An optical device according to any one of claims 1 and 2, characterised in that the angles of intersection of at least a part of the prisms formed on the inner surface of at least one globe are rounded.

4. An optical device substantially as described above and illustrated in Figures 2, 3 and 4 of the accompanying drawings.