Light Signal

#Field of the Invention

#The invention relates to a light signal, in particular for rail-bound traffic routes, having a light source, an optical system and a control device for adjusting an emission characteristic.

#In principle, light signals serve as signal emitters or symbol indicators which impart particular information by means of coloring and/or shaping of a luminous surface, that is, by means of the emission characteristic. This often involves safety-related information which must not be optically falsified or overlaid with extraneous light. The unwanted lighting up or falsification of a light point by the ingress of ambient light, for example sunlight or headlamp light is designated a phantom effect. By means of the phantom effect, in extreme cases, a false indication can occur due to an untimely illumination of a light point or a color shift. This effect is particularly disturbing when LED arrays are used as the light source, since LEDs can be stimulated to luminesce by incident light and in the case of LED light sources, rear reflectors are often used. Apart from the phantom generators which are predictable with projection, for example, a low sun for signals in an east-west orientation, sporadic or unforeseen sources also arise as phantoms, for example, vehicle or building lights, reflection at surfaces, for example, on glazed facades or snow coverings. Thus a signal which is intended to be phantom-proof by virtue of the location can be phantom-prone. In general, the attempt is made to minimize the phantom effect through shades, shields, the avoidance of east-west orientation or by the repetition of critical signals.

#The invention will now be described in greater detail by reference to the illustrations in the figures. In the drawings:

#FIG. 1 is a schematic representation of the light signal of known construction, described above, and

#FIGS. 2-4 are three exemplary embodiments of light signals of known construction in the same manner of representation as FIG. 1.

#FIG. 2 shows a light signal in which in place of the front panel (6, FIG. 1), a smart glass element (9) is provided. The transmittance of the smart glass element 9 and thus the brightness of the light signal is adjusted with the control device 7. The usual brightness adjustability of the light source 2 according to FIG. 1 is therefore dispensable. In the exemplary embodiment, the smart glass element 9 consists of two separate transmission controllable smart glass panels 10 and 11. By this means, the switchover between day and night operation is simplified. Furthermore, a blink function can also be realized through alternating control of the smart glass panels 10 and 11 when the desired blink frequency is not implementable due to too high a switching time of a single smart glass panel 10 or 11.

#FIG. 3 shows a light signal with phantom light reduction. In place of the front panel (6, FIG. 1), a smart glass element 9′, the transmission of which is adjustable by means of the control device 7 dependent upon measurement values of an extraneous light sensor 12, serves this purpose. In order to compensate for the increasing graying-out of the smart glass element 9′ with relatively strong phantom effect, the control device 7 simultaneously increases the light intensity of the LED light source 2.

#The exemplary embodiment represented in FIG. 4 shows a combination of the brightness regulation according to FIG. 2 with the smart glass element 9 and the phantom light reduction according to FIG. 3 with the smart glass element 9′ and a further smart glass element 9″ for light flux deflection relative to the optical axis. It is evident that the smart glass element 9″ is arranged between the LED light source 2 and the optical system 3. In the exemplary embodiment, the smart glass element 9″ consists of two separate smart glass panel segments 13 and 14, which protrude differently far into the light flux. Apart from the control signals for the smart glass elements 9 and 9′, the control device 7 also generates the control signals for the transmittance of the smart glass panel segments 13 and 14. The latter control signals can certainly be different in order to adjust the desired spatial light distribution, in particular depending on the respective track geometry.