A LIGHT DEVICE, ESPECIALLY FOR AIRPORTS AND ROADS

Abstract: At least one lamp (3a, 3b) is disposed in a casing (1) having a transparent, flat cover (2), from which a well-defined light beam is emitted. The cover has a planar external surface (9) and a stepped internal surface (8). The lamp (3) is adapted to emit light rays (L₂) impinging substantially at right angles on the stepped surface portions of the cover, so that the light rays, upon refraction at the planar external surface, are emitted at a desired small angle.

Description: "A light device, especially for airports and roads" The invention relates to a light device, especially for airports and roads, comprising at least one light source disposed in a casing having a light pervious, substantially flat cover, from which a light beam, generated by the light source, emerges. Airports normally utilize special light devices for marking the centre lines on take-off and landing runways as well as taxiways. Similar devices, so called guidelights, are also mounted on the parking places of an airport. The requirements on such light devices which are normally mounted as units, are strict and can in practice only be fulfilled at considerable costs. The light devices of this kind must emit a well-defined.light beam in a certain direction, particularly at a very small angle to the ground, and they also have to be reliable in operation and be resistant to dirt, rain, snow, ice and rough treatment, e.g. in connection with snow clearance. However, these light devices often cause difficulties in that the bulbs or light sources develop much heat which results in the melting of snow and the forming of ice. So far, generally two types of such light devices have been used, namely,on the one hand, open, flat devices and, on the other hand, closed,-protruding devices. The open, flat typ (mostly provided with slots)) permit the use of steel scrapers in case of snow clearance in order to clean the runways satisfactorily and to meet the demands regarding braking action of aircrafts. This type, however, needs to be cleaned at short intervals by means of special equipment. The other type, i.e. the closed, protruding type, requires the use of rubber scrapers for snow clearance, and therefore the demands on braking action will not always be met. Moreover, the use of rubber scrapers over the runway surface will often result in a non-uniform clearance. Therefore, in such cases, it is necessary to additionally spread out sand and urea and to carry out blow sweeping to an increased extent. An advantage of the latter type of device is that it does not need to be cleaned as often as the open, flat type. The object of the invention is to accomplish a light device which is flat as well as closed and which thus combines the advantages of the previously known devices. This object is achieved in that the cover, which consists of a transparent material, has a substantially planar external surface and a stepped internal surface, in that the light source is arranged in such a way that the light rays emitted therefrom enter the stepped surface portions of the inside of the cover substantially at right angles, and in that the inclination of the stepped surface portions and the refractive index of the cover material are adapted so that the light rays upon refraction at the external surface of the cover emerge therefrom at a desired small angle. Since the external surface of the cover is entirely planar, the whole light device can be made fully flat and closed at the top, thereby considerably facilitating cleaning as well as snow clearance. Moreover, it is possible to achieve a well-defined emitted light beam of high indensity, because the light rays generated by the light source impinge on the opposite stepped surface portions generally at right angle at the inside of the cover, and when emerging therefrom (from an optically dense medium into an optically thin medium) they are refracted away from the normal of the external surface of the cover. Hereby, the losses due to reflection at each interface are reduced to a minimum. Even if a colour filter is inserted in the beam path, the intensity of the emitted light beam can be of such a high value that, in spite of the use of a relatively weak light source, the international standards can be satisfied. A further very essential advantage of the invention is that the above-mentioned refraction away from the normal at the external surface of the cover enables the emission of an intensive beam being directed at as small an angle relative to the cover plane as desired. The emitted light beam can practically sweep in parallel to the ground surface. This is hardly possible to achieve by means of the previously known light devices. As compared to the known light devices provided with slots, a further advantage of the inventive device is that it is possible to achieve a certain, although relatively diffuse light distribution sideways. Hereby, a marking light can be made visible even from the side, e.g. in curves, crossing taxiways or the like. In order to achieve a well-collected emitted light beam, as sometimes required, the inventive light device should preferably permit the light rays from the light source to impinge onto the internal stepped surface portions at a well-defined, preferably right angle, so that all the light rays propagate obliquely through the cover in parallel each other and are all refracted at the top surface of the cover in exactly the same way. This would require a wellcollimated light beam emerging from the light source and, consequently, an optic system of very high quality between the light source and the cover. However, in a preferred embodiment of the invention, the cover consists of several inclined discs which are made planar at the external side of the cover and form the stepped surface portions at the inside. The discs are separated from eachbtherbymeans of a light absorbing or light reflecting interface layers. In such an emobidment of the light device, not only exactly parallel light rays can emerge from the light source, since the non-parallel rays will be "filtered out" by absorption or reflection (and subsequent total reflection at the top, planar surface of the cover). A conventional parabolic reflector has turned out to be sufficient to obtain a substantially parallel light beam. The total manufacturing costs of the light device can therefore be kept down at a favourably low level. Thanks to the additional advantages mentioned above, the operational costs can also be considerably reduced in comparison with the prior art light devices. A preferred embodiment of the invention will be described further below with.reference to the drawings. Fig. 1 shows schematically a light device as seen from above Fig. 2 shows a central section through the device shown in Fig. 1; Fig. 3 shows, in a larger scale, a partial longitudinal section through the cover of the device, illustrating the paths of various light rays; and Fig. 4 shows a corresponding longitudinal section through the cover of a modified embodiment having interposed aluminium layers. The light device shown in Figs. 1 and 2 comprises a boxlike casing 1, which is installed in the ground in such a way that the upper surface of its transparent cover 2 is aligned with the ground surface. In the illustrated example, the light device serves as a marking lighton the centre line of a take off or landing runway cr a taxiway at an airfield. The device could be used as well on roads or high ways or generally at any place where a well-defined light beam is desired. In the casing 1, two light sources (e.g. light bulbs) 3a, 3b are mounted with conventional parabolic reflectors 4 on a bracket 5 fastened at the side-walls of the casing. The electrical supply conductors 6 of the light sources are connected to an external cable (not shown) preferably via a fuse, so that the light sources can be energized from a central power source. In the illustrated example, each light source may have a power of appr. 50 Watts. The two light sources 3a,3b (see Fig. 1) are disposed on each side of the longitudinal centre line C of the device, and directed obliquely upwards. The light beams emitted from the two light sources emerge towards the centre line C at an angle o( so that the light beam emerging from the light device has an aperture angle of appr. 20( In case coloured light is desired,e.g. green light for marking the centre line of a runway, a colour filter 7 can be inserted in the path of the beam between the light source 3 and the casing cover 2. As appears from Fig. 2, the light beams propagate obliquely upwards towards the cover 2. The latter is made of a transparent material, preferably a clear epoxi resin (obtainable e.g. from the firm Nils Malmgren AB, Sweden, under No. 520 430). According to the invention the underside or internal surface 8 of the transparent cover 2 is formed with steps, whereas the external surface 9 of the cover is flat or planar. The design of the two surfaces 8 and 9 is such that the light rays (compare ray L2 in Fig. 3) emitted from the light source 3 impinge substantially at right angle on the stepped surface portions of the inside of the cover and are refracted away from the normal at the external surface of the cover. In this way, it is possible to obtain an emerging light beam which, in spite of only a small reduction of intensity, propagates almost along the ground surface. The stepped internal surface 8 of the cover can be produced by making the cover 2 of identical plates or discs, which are oriented obliquely and joined together by fusion or glueing. The side opposite to the stepped surface is then filled out with a clear epoxi resin and/or ground to become smooth, so that a fully planar external surface 9 of the cover is obtained. The interfaces between the discs (indicated by dashed lines in Fig. 3) are light absorbing or reflecting, e.g. in the form of fabric reinforcement strips, in order to secure that scattered light rays cannot pass over from one disc into an adjacent one. The emitted light beam will in this way be strictly limited between two definite angles in the vertical plane relative to the normal, these angles being designated as ssl and A3 in Fig. 3 for the two extreme light rays Ll and 113. For a given value of the refractive index nl (= 1.47 for the epoxi plastic of the kind referred to above, whereas the refractory index of air is assumed to be 1,00) it is possible to adapt the thickness -h of the cover 2 and the thickness d of each disc in such a way that the light beam emitted from the cover lies between the desired angles ss1 and On the basis of the relatively simple geometry in Fig.l and the Schnell law of refraction, the following relationships can be obtained: sin disc inclination angle K = arc sin n ss2 (1) disc thickness d = h x tan (6 -z1) (2) cos &alpha;1 maximum angle of beam zl= arc sin sin ss1 (3) n1 Assuming the values: nl = 1.47 h = 15.0 mm d = 0.98 the relationships (1), (2) and (3) will give: &gamma;( = 42,8 or Q #1 = 40.0 1 71.00 2 = 87.0 The maximum light intensity of the emitted beam is thus obtained at an angle of 3 relative to the ground surface. The maximum angle (for the ray L1) is only 190 relative to the ground surface. The discs constituting the cover 2 function as Venetian blinds, although the impinging light beam is refracted towards the plane of the cover. In the embodiment of Fig 4, thermally conducting metal layers, preferably sheets 10 of aluminium, are inserted between the inclined discs of the cover. These metal layers will hereby secure an effective transfer of heat away from the inside of the casing, which is important, since the light sources will necessarily emit a great deal of heat apart from the visible light. By leading away the heat to the ambient air, the risk of overheating is reduced, and more powerful light sources can be installed, if desired or required. In other modified embodiments of the invention, it may be sufficient to place only one light source 3 in the casing 1. If two light sources 3a and 3b are used, the emission direction of each light source in the horizontal plane may be different in order to achieve the desired beam distribution, either symmetrically (2 according to Fig. 1) or assymmetrically, the latter exemple being applicable in curves of taxiways or the like. Finally, it is advantageous to embed granular particles (not shown) into the material forming the cover 2, especially at the external surface 9. The upper edges of such particles are preferably located in the ground level, as described in the published Swedish patent application 7803611-8.

Claims: CLAIMS 1. A light device, especially for airports and roads, comprising at least one light source disposed in a casing having a light pervious, substantially flat cover, from which a light beam, generated by the light source, emerges, c h a r a c t e r i z e d in that said cover (2), which consists of a transparent material, has a substantially planar external surface (9) and a stepped internal surface (8), in that said light source (3) is arranged in such a way that the light rays (L2) emitted therefrom enter the stepped surface portions of the inside of the cover substantially at right angles, and in that the inclination of the stepped surface portions and the refractive index of the cover material are adapted so that the light rays, upon refraction at the external surface (9) of the cover, emerge therefrom at a desired small angle. 2. A device as set forth in claim 1, c h a r a ct e r i z e d in that the cover (2) consists of a plurality of inclined discs, which are levelled into a plane at the external surface (9) of the cover by means of a clear filler and/or by grinding and which form, at the internal surface (8) of the cover, said stepped surface portions, and in that the discs are separated from each other by light absorbing or light reflecting interface layers. 3. A device as set forth in claim 1 or 2, c h a r a ct e r i z e d in that inclined layers (10) of thermally conducting material are inserted in the cover (2).

Inventors: DAHLBERG, ANDERS
Applicants: META-FER AG
Application year: 1980
Main classification: F21Q3
IPC codes: B64F1, F21S8, E01F9