AN AIRFIELD MARKER LIGHT

Abstract: An airfield marker light, comprising a casing to be flush-mounted in the ground and having a lower light source (4), an upper, a transparent cover plate (8) lying substantially in the ground plane M, and optical means (7), which divide the light bundle from the light source, so that two light beams (L12, L34) are emitted from the upper surface of the cover plate (8) in opposite directions at a small angle to the ground plane. According to the invention, the light source (4) emits a collected, substantially vertical light bundle, and the optical means include a light dividing prism (7) situated between the light source and the cover plate and having refractive planar surfaces (7a, 7b, 7c, 7d) obliquely oriented in opposite directions, so that the vertical light bundle is divided into two light bundle portions, directed obliquely upwardly in opposite directions, said light bundle portions upon passage through the cover plate, being refracted in opposite directions in the upper surface (8a, 8b) of the cover plate.

Description: AN AIRFIELD MARKER LIGHT The- invention relates to an airfield marker light, e.g for runways or taxistrips . The marker light is of the flush- mounted type and provides light beams directed in opposite directions at a small angle with the ground, as defined m detail in the preamble of claim 1. Such a marker light is known from GB-A-966-357 (Canadian Patents 8e Development), wherein the light from a lower, non-direct ve light source strikes, on the one hand, two part-cylmdricl collecting lenses each positioned adjacent to a saw-tooth surface, these lenses serving to focus the light into a respective light bundle with parallel rays, and on the other hand, somewhat curved reflector surfaces, located at the bottom adjacent to the side walls of the casing, these reflector surfaces serving to reflect the light toward the saw-tooth surfaces of the cover plate. Wit this arrangement, it is difficult to avoid that a large por tion of the light strikes the saw-tooth surfaces at an ob¬ lique angle with an accompanying total reflection, absorp¬ tion and heat development in the cover plate. This is also due to the fact that each collecting lense co-operates with no more than two saw-tooth surfaces and that the light source has a large radial extension in relation to its dis¬ tance from the collecting lenses and the reflector surfaces Consequently, this marker light provides a relatively low light efficiency and, if the power of the light source is increased, the heat development will be too high. A similar marker light is known from DK-C-113912 (Siemens AG) , wherein a lower, point-like source emits non-directive light, which hits an upper, transparent cover plate having an upper planar surface and an incident surface, which has the shape of a toroid and which is discontinued by two dia- metrically opposed collecting lenses or planar cylinder lenses, the latter collecting the light into two light beams being emitted from the upper surface of the cover plate in opposite directions. Even in this structure, the heat deve- lopment will be strong, and it is therefore hardly useful in practical applications, since the required light intensity cannot be achieved. Other examples of previously known marker lights of the lush-mounted type, although emitting light in only one main direction, are given in EP-B1-22106 (Meta-Fer AG) and US-A-3 096 024 (Young) , these two lights including a transparent cover plate having a planar upper surface and a saw-tooth lower surface. The light source is obliquely positioned, in this case so that its light bundle strikes substantially at right angle onto one of the surfaces of each saw-tooth. In principle, these known lights can be supplemented by a second light source', inclined in an opposite direction, so that two oppositely directed light beams are obtained. However, such an arrangement is disadvantageous because of- the complications involved in arranging two separate light sources, and because of the increased heat development caus¬ ed by another light source. The ob ' ect of the invention is to achieve a marker light having only one light source and ensuring a division of the light bundle into two oppositely directed, sufficiently strong light beams with a moderate heat development. More¬ over, the structure should be fairly simple and relatively non-expensive in manuf cture. This obj ' ect is achieved for a marker light according to the invention, which is characterized in that the light source is adapted to emit a collected upwardly directed light bundle, and that the optical means include a light dividing pris in the form of a transparent plate body being locate between the light source and the cover plate and having oppositely inclined, refractive planar sur- faces, so that the upwardly directed light bundle fr the light source, during its passage through the lig dividing prism, is divided into two obliquely upward directed light bundles propagating in opposite direc tions at right angle to the respective saw-tooth sur f ces . By this structure, the light energy generated by the light source is utilized to a very great extent as useful, emerg ing light, wheras only a minor part thereof is converted to heat. Moreover, the upper cover plate, which is exposed to mechanical forces, s thermally protected by the under¬ lying light dividing prism. However, the most important feature is that it is possible to obtain substantially higher light intensity, with a moderate heat development, than with the previously known solutions. The light efficiency can be be especially high by adapting the light dividing prism to emit two mutually partially overlapping light bundles (compare claim 2) . If desired, practically the whole cover plate can then be utilized for light emission. A further increase of the light intensity near the ground level can be achieved in that the upper surface of the cover plate includes two portions, being slightly inclined in opposite directions, and each emitting a light beam, as defined m claim 8. Useful embodiments of the light dividing prism are given in claims 3 through 7, whereby the advantageous features dis¬ cussed above are entranced still urther. The marker light may, according to claims 9 and 10, be de- sigted for narrow emitted light beams, being diametrically αppαsed, which is preferable at straight portions of a run¬ way, or for wider light beams, being obliquely directed sideways, which is preferable at curved portions of a taxi- strip or the like. The invention will be explained more fully below with re¬ ference to the appended drawings, which illustrate a pre- ferred embodiment. Fig. 1 shows a marker light according to the invention in perspective view, half of the device being cut away through a central, vertical section for increased clarity; Fig. 2 shows the marker light from above; Fig. 3 shows the optical components, schematically with the principal light rays; and Figs. 4a and 4b show central sectional views of the lower part of the marker light with a lamp in two mounting posi¬ tions . The marker light shown in Figs. 1 and 2 comprises an essen¬ tially cylindrical casing 1 of metal, e.g. an aluminum alloy, having a bottom plate la and an upper, substantially rectangular seat lb, a reflector lamp 4, mounted on the bottom plate la by means of a bracket 2, with a mounting plate 3, a colour filter 5, a transparent heat insulating plate 6, a refractive plate 7, and an upper transparent cover plate 8 tightly mounted in the seat lb. As indicated in Fig. 1, the casing 1 is disposed in a well housing 9 having a lid 10, so that the upper surface of the cover plate 8 lies substantially flush with the ground plane. ' The upper, substantially rectangular cover plate 8 is preferably made of a transparent epoxy plastic material, i.e. an abrasive resistant material, which, if necessary, can be provided a new surface layer for filling out possibl scratches or repairing other damages on the upper surface. However, to avoid such damages, hard, ceramic particles are partially embedded into the surface layer partly along two longitudinal edge portions 11,12, partly along a central, transverse strip portion 13. Hereby, the upper surface of the cover plate is divided into two rectangular portions 8a, 8b each intended to emit a light beam, which propagates close to the plane of the ground (compare Fig. 3) . In order to achieve the best possible light intensity near the plane of the ground, each surface portion 8a, 8b is somewhat ln- clmed, so that it inclines downwards from the central transversal portion 13 about 3° relative to the horizontal plane . * As .appears from Figs. 1, 4a and 4b, the bracket 2 for the reflector lamp 4 consists of a bended metal strip, e.g. of an aluminum alloy, which is oriented substantially in parallel to the tranversal central portion 13 of the cover plate 8. One end portion 2a of the bracket is fixed to the bottom plate la, which likewise can be made of an aluminum alloy, in a good heat conductive contact with latter. The other, longer end portion 2b is planar and horizontal, and the rectangular mounting plate 3 is secured to this portion by a screw fastener 14. The reflector lamp 4 with its socke 4a can be mounted on the plate 3 either in a central, straight upwardly directed position according to Fig. 4a or in a somewhat oblique (m a plane through the central trans versal portion 13 of the cover plate 8) position in a cor¬ responding recess 3a the plate, as appears from Fig. 4b. The electrical feeding wires 15a, 15b of the lamp 4 are draw through a central hole 16 the bottom plate la, as appear from Fig. 1. The colour filter 5, which is disposed somewhat above the reflector lamp 4, is made of a toughened glass plate with colouring pigment, the glass plate 5 being hori¬ zontal and all around sealingly fitted circumferentially to the cylinder casing 1. The circumferential portion thereof is secured between two cylindric tube portions 17,18, like¬ wise of an aluminum alloy, said tube portions being tightly fitted internally in the the tube casing 1. The insulating glass plate 6 is likewise horizontal and rests on the upper end of the upper tube portion 18, the circumferential edge thereof fitting sealing to the sur¬ rounding tube casing 1. The refractive plate 7 is likewise horizontally disposed and is sealingly fitted to the surrounding tube casing 1 at a " small distance below the upper cover plate 8. A portion of the heat, which is generated by the reflector lamp 4, is passed away by heat conduction via the socket 4a, the plate 3, the bracket 2 and the bottom plate la, and a portion of the heat generated during the passage of the light through the plates 5, 6 and 7 is passed away by way of the heat conductive contact with the tube casing 1. The in- sulating glass plate 6 also serves to prevent an upward transport of heat by convection. Thus, the upper cover plate 8 can be maintained at an advantageously low temperature, whereby its resistance is increased and the life of the marker light is substantially increased in relation to kown solutions . The optical features will now be described with reference to Fig. 3. The vertically directed reflector lamp 4 emits a well defi ed, collected light bundle, which in ground marker lights intended for straight portions of a runway or a taxistrip diverge about 10° at the most, as appears from the longitu dmal section in Fig. 3. Since the plates 5 and 6 are mu¬ tually parallel, the light bundle passes through these plates without any geometrical change. The refractive plat 7, however, is provided with inclined surfaces 7a ,7b,7c an 7d and thus serves as a light refracting prism, which divi es the light bundle into two bundle portions L-j_,L2 and L3, respec ively, directed obliquely upwardly in opposite direc tions (between the light refracting plate 7 and the cover plate 8). The underside of the cover plate 8 is saw-toothed shaped m a the transversal direction (in parallel to the portion 13 at the upper side), wherein each saw-tooth has a oblique saw-tooth surface 8c, which is normal to the obliqu light bundle portion L j _,L2 » and an adjoining inclined saw¬ tooth surface 8d, which is normal t.o the other oblique ligh bundle portion L3 , L4. The two oblique light bundle portions will therefore strike onto the underside of the cover plate without refraction, whereupon each light bundle portion s heavily refracted in the respective upper surface portions 8a and 8b, so that the emitted light beams _2 and L34 are directed longitudinally in opposite directions at a very small angle to ground plane M (dash-dotted in Fig. 3) . It should be noted that no light strikes the upper transversal portion 13 of the cover plate, m which hard particles are embedded (compare Fig. 2) . To achieve the desired light efficiency, it is preferable that the light refractive plate 7 is so designed and posi¬ tioned adjacent to the cover plate 8 that the obliquely up¬ wardly directed light bundle portions partially overlap eac other, namely the bundle portions L2 and L3. For this pur- pose, the light refractive plate 7 is situated with a small distance between its upper, planar surface and the lower saw-tooth surface of the cover plate 8. Furthermore, the refractive plate 7 includes two outer incident surfaces 7a r 7d being obliquely oriented in opposite directions, and two inner incident surfaces 7b, 7c located therebetween and likewise oriented obliquely in opposite directions. The four incident surfaces 7a, 7b, 7c and 7d ad ' oin each other and form together the shape of the letter M with oblique legs. The surfaces 7a and 7c are mutually parallel and refract the bundle portions L^ and L2 respectively, which together form the emitted light beam L_2 upon being further refracted in the surface portion 8b of the cover plate. The surfaces 7b and 7d are likewise mutually parallel and refract the bundle portions L3 and L4, so that the latter bundle portions, up- on refraction in the upper surface portion 8a of the cover plate, form the oppositely directed light beam L34. If de¬ sired, more oblique surfaces coresponding to the surfaces 7b and 7c can be formed between the outer oblique surfaces 7a and 7d, e.g. in a saw-tooth pattern corresponding to the underside of the cover plate 8. For the be-st possible light efficiency, the intermediate oblique surfaces (7b, 7c) should have a vertical extension which is less than that of the outer oblique surfaces 7a and 7d. In principle, the light refractive plate 7 could be replaced by separate prisms with corresponding oblique surfaces, but a unitory plate is preferable from the view of easy mounting as well as from the view of efficient heat transfer to the surrounding casing. The light rays according to Fig. 3 correspond to the loca¬ tion of the reflector lamp 4 according to Fig. 4a. If the reflector lamp 4 is obliquely positioned according to Fig. 4b, the light rays will be principally the same as those in Fig. 3, since the reflector lamp 4 is inclined only in a transversal plane (normal to the drawing plane in Fig. 3) . Thus, the oblique position according to Fig. 4b will only result in that the light beams L^2 anc * ^34 are turned some ¬ what sideways, which can be used e.g. in curved sections of a taxistrip. If desired, the reflector lamp 4 can be pro- vided with another reflector, which gives a somewhat wider light bundle, e.g. diverging up to 50°, so that the spread sideways is correspondingly increased. The spread in the central longitudinal plane according to Fig. 3, however, will not be increased, since the light rays, which diverge more than about 5° from the vertial direction, will be more inclined between the light refracting plate 7 and the cover plate 8, so that they are refracted in the outer incident surfaces 7a and 7d and are totally reflected in the upper surface portions 8a, 8b of the cover plate 8. If it is de- sired to reduce the heat, which is hereby generated by the absorption of light in the cover plate 8, one can use a re¬ flector, which spreads the light bundle up to 50° sideways but on,ly. about 10° in the longitunal direction.

Claims: CLAIMS 1. An airfield marker light comprising a casing (1) to be flush-mounted in the ground and having - at least one lower light source (4), an upper, at least partially transparent cover plate (8) with a lower saw-toothed surface (8c, 8d) and an upper, substantially planar surface (8a, 8b), which upon lowering the casing into the ground (M) lies essentially flush therewith, and - optical means (7) adapted to direct the light from the light source in such a way that two light beams ^2, L34) are emitted from the upper surface of the cover plate (8) in opposite directions at a small angle with the ground plane (M) , c h a r a c t e r i z e d in - that said light source is adapted to emit a collected, upwardly directed light bundle, and - that said optical means include a light dividing prism in the form of a transparent plate body (7) being located between the light source and the cover plate and having oppositely inclined, refractive planar surfaces (7a, 7b, 7c , 7d) , so that the upwardly directed light bundle from the light source (4) , during its passage through the light dividing prism, is divided into two obliquely upwtrdly directed light bundles propagating in opposite directions at right angle to the respective saw-tooth surfaces (8c, 8d) . 2. Marker light as defined in claim 1, c h a r a c t¬ e r i z e d in that said light dividing prism (7) is adapted to emit two obliquely upwardly directed light bundles, which partially overlap each other. 3. Marker light as defined in claim 1 or 2, c h a r a c t e r i z e d m that said plate body (7) is horizontally disposed with an upper planar surface and lower, symmetrically situated incident surfaces (7a, 7b, 7c 7d) being obliquely oriented in opposite directions. 4. Marker light as defined in claim 3, c h a r a c t¬ e r i z e d in that said incident surfaces includes two outer incident surfaces (7a, 7d) obliquely oriented in opposite directions and at least two inner incident surfac (7b, 7c) located therebetween and being likewise obliquely oriented in opposite directions. 5. Marker light as defined in claim 4, c h a r a c t¬ e r i z e d m that each of the outer incident surfaces (7a, 7d) adjoins a corresponding one of two inner, mutually adjoining incident surfaces (7b, 7c). 6. Marker light as defined in claim 5, c h a r a c ¬ e r i z e d in that the four incident surfaces (7a, 7b, 7c , 7d) form the shape of the letter M with oblique legs . 7. Marker light according to anyone of claims 4 - 6, c h a r a c t e r i z e d in that the outer incident surfaces (7a, 7d) have a greater vertical extension than the inner incident surfaces (7b, 7c) . 8. Marker light as defined in anyone of the preceding claims, c h a r a c t e r i z e d in that the upper surface of the cover plate (8) includes two portions (8a, 8b being slightly inclined in opposite directions and each emitting a corresponding one of said two light beams CL 12> 34 • 9. Marker light as defined in anyone of the preceding claims, c h a r a c t e r i z e d in that the light source (4> is provided with a reflector, giving an emitted, vertic¬ al light bundle, which diverges no more than 10°. 10. Marker light as defined in anyone of claims 1 - 8, c h a r a c t e r i z e d, in that the light source (4) is obliquely adj ' ustable sideways (Fig. 4) and is provided with a reflector giving a light bundle, which diverges no more than 50°.

Inventors: DAHLBERG ANDERS, DAHLBERG, ANDERS
Applicants: FRANSCH AB
Application year: 1987
Main classification: B64F1
IPC codes: B64F1, E01F9, F21S2, F21S8