TECHNICAL FIELD

The disclosure relates to the field of optics, and more particularly to optical systems for railway signals.

BACKGROUND

A railway signal is a safety relevant device and a lot of requirements must be fulfilled, concerning color, intensity, faulty behavior and visibility in all circumstances, especially in certain sunshine conditions. Signals are normally mounted on masts next to the railroads and above the train level, and tilted at a small angle downwards to be focused on an average driver position at some hundred meters distance. When the sun is shining on the signal at a certain angle, the signal may seem to be switched on when it is not, due to the sun reflection. This phenomenon is called phantom light and it can lead to misinterpretation of the signal status, potentially causing accidents. The problem is less prevalent in older signals with filament bulbs, as the light source is a small filament and the sunlight normally does not reflect off its position. However, in Light-Emitting Diode (LED) based signals the light sources have a larger area and often are placed on a board with other optics, so the reflection is more likely .

Reduced phantom light is one of the features that may be necessary for safe recognition of railway signaling systems. Others include high axial light intensity, a narrow beam angle, uniformity of brightness and appropriate thermal conditions within the system. These requirements present a challenge for manufacturers of LED-based railway signals. Additional challenges arise from existing variations in colors of LED-s used. SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

It is an objective of the present invention to provide a new and improved optical system for railway signals that would satisfy and possibly exceed the requirements in various railway signals of different sizes and colors, including the requirements for phantom light. It is a further objective to provide a new lens for a railway signal based on LED-s designed to reduce phantom light of the railway signal and provide mixing of light emitted by LED-s.

The foregoing and other objectives are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, an optical system for railway signals is provided. The optical system comprises a frontal body section and a rear body section attached to the frontal body section. The rear body section comprises a light source comprising one or more light-emitting diodes, a rear lens at least partially covering the light source, and a light-absorbing structure surrounding the rear lens. The frontal body section comprises a converging frontal lens arrangement positioned such that the rear lens is substantially in the focal point of the frontal lens arrangement, and a casing connecting the frontal lens arrangement to the rear body section. The rear lens is configured to pass light collected from the light source towards the frontal lens arrangement, and the rear lens also comprises a cut-out under a substantially horizontal line below its center. The light-absorbing structure surrounding the rear lens covers the cut-out of the rear lens, and is configured to absorb light coming from the direction of the frontal lens arrangement. The terms "frontal" and "rear" in this description refer to positioning in relation to the direction of emitted light, wherein rear refers to a position close to (or behind) the light source, and frontal refers to a position at a predetermined distance from the light source in the direction of emitted light. These indications are not to be interpreted as limiting or describing the shape of the optical system. A horizontal line below the center of the rear lens refers to a line which is substantially horizontal in relation to the ground surface once the signal is installed. The line may be straight or slightly curved depending on the shape of the rear lens.

A focal point of the converging frontal lens arrangement means an approximate focal point location. The frontal lens arrangement may comprise one converging lens or two and more lenses which form a converging lens arrangement. The frontal body may be attached to the rear body by various means, rigidly or detachably via the casing. The light-absorbing structure may comprise light-absorbing material, or for example be covered in mat black color. The light-absorbing structure is positioned to surround the rear lens perimeter and follow the shape of its outline. This includes the cut-out of the rear lens, so the area under the horizontal line remains covered by the light-absorbing structure.

The arrangement of the optical system wherein the rear lens has a cut-out covered by the light-absorbing structure according to the first aspect provides an effect of minimized phantom light. This effect is especially relevant in situations where the sunlight or any other external source of light has low elevation of a few degrees above horizon. Due to optical properties of a converging frontal lens arrangement, the light from an external light source with low elevation (such as the sun) focuses by the frontal lens arrangement slightly lower than its horizontal focal point, and the cut-out in the lower part of the rear lens provides a light absorbing spot below the focal point, which prevents unwanted reflections. At the same time, the shape of the rear lens according to the first aspect has little to no effect on the active light passed through the rear lens towards the frontal lens arrangement.

In an implementation of the optical system according to the first aspect, the light-absorbing structure comprises a light-absorbing element having the shape of a conical torse with two openings having a smaller and a larger area, wherein the opening having a smaller area surrounds the rear lens and the opening having a larger area faces towards the frontal lens arrangement, and wherein the light-absorbing element comprises light- absorbing material on the inner surface of the conical torse .

By conical torse is meant a geometric shape of a cone with openings on both sides, the smaller opening surrounding the rear lens. The conical torse provides a geometrical structure that allows the light coming from an outside source into the system through the frontal lens arrangement to be spread over a larger area of the conical torse walls, instead of focusing into a small dot. Apart from preventing unwanted reflections, the light-absorbing element shaped as a conical torse also reduces inner temperature and improves the longevity of the system.

In a further implementation of the optical system according to the first aspect, the opening of the light absorbing element having a smaller area is shaped to match the shape of the rear lens comprising a cut-out below its centerline. In this implementation, walls of the conical torse start at the perimeter of the rear lens .

In a further implementation of the optical system according to the first aspect, inner surface of the conical torse comprises a plurality of triangular ribs covered with light-absorbing material. These ribs may be radially spread around the inner surface of the conical torse. The triangular ribs may have an acute angle pointing toward the central axis of the conical torse. This implementation may have an effect of forming a light-trap, meaning that light rays coming from any direction are absorbed and partly reflected at least twice off the walls of each triangular rib. In a further implementation of the optical system according to the first aspect, the inner surface of the casing connecting the frontal lens arrangement to the rear body section is covered with light-absorbing material. This can further improve light absorption of the optical system and prevent unwanted reflections from the inner walls of the casing. In a further implementation of the optical system according to the first aspect, the rear lens has an elliptic or circular outer perimeter with a cut-out portion under a substantially horizontal line below its center. This implementation includes lenses of various shapes but having an elliptic or circular outer perimeter .

In a further implementation of the optical system according to the first aspect, the rear lens has the shape of a dome comprising a cut-out under a substantially horizontal line below its center, wherein the dome has facetted surface structure. This structure has an effect of mixing and focusing of light emitted by the light sources towards the frontal lens arrangement.

In a further implementation of the optical system according to the first aspect, the rear lens comprises a grid of domes configured to spread light passed from the light source towards the frontal lens arrangement. This structure has an effect of reduced brightness of light passed towards the frontal lens arrangement. Reduced brightness may be needed for example due to physical properties of LED-s of certain color. The frontal lens arrangement in this implementation can still remain evenly lit by the rear lens passing light from the light sources. A facetted dome, a grid of small domes or other types of rear lens surface features may be referred to as light mixing elements.

In a further implementation of the optical system according to the first aspect, the rear lens comprises a superposed cylindrical structure. This provides a further surface feature of the rear lens suitable for horizontal spreading of light, to get a better horizontal mixing of two LEDs in a row and minimal vertical spreading .

In other implementations of the optical system according to the first aspect, the rear lens may be a regular lens with a cut-out under a horizontal line below its center, but without additional surface features.

In a further implementation of the optical system according to the first aspect, the rear lens comprises dimming material that limits the intensity of light emitted by the light source. This implementation may improve operation of a railway signal that has higher light intensity than is allowed.

In a further implementation of the optical system according to the first aspect, the rear body section comprises a casing enclosing the light source and surrounding the rear lens to prevent light emitted by the light source from escaping the optical system outside of the rear lens location. In a further implementation of the optical system according to the first aspect, the light source comprises two or four LEDs of the same color. In a further implementation of the optical system according to the first aspect, the rear body section comprises a controller and electrical circuitry driving the light source. The controller may be configured to control the intensity of light throughout the lifetime of the railway signal.

In a further implementation of the optical system according to the first aspect, the rear body section comprises two or more light sensors configured to measure the intensity of light emitted by the light source at a predetermined location in the rear body section, and to provide light intensity readings to the controller; wherein the light-absorbing structure is configured to prevent light coming from the direction of the frontal lens arrangement from reaching the two or more light sensors .

A technical effect of this implementation is that light sensors can independently measure the light intensity of LED-s and are protected from sun and scattered environmental light. This allows adjustments of intensity of light emitted by the LEDs based on their performance, to keep the brightness on the same level over lifetime of the railway signal. An end-of-live- message may also be generated because of internal control of LED-brightness .

In a further implementation of the optical system according to the first aspect, the rear body section comprises a flat board; the light-emitting diodes of the light source are positioned on the flat board under the rear lens; and the two or more light sensors are positioned on the flat board outside of the rear lens perimeter. The flat board may also be referred to as an LED-board in this specification, without limitation.

In a further implementation of the optical system according to the first aspect, the rear lens comprises a light-bending portion at its perimeter; the two or more light sensors are positioned symmetrically on the flat board in relation to the light source position; and the light-bending portion is configured to pass a portion of the emitted light directly onto the two or more light sensors. The portion of emitted light which does not go towards the frontal lens arrangement is passed through the light-bending portion directly at a flat angle onto the light sensors. In a further implementation of the optical system according to the first aspect, the rear lens comprises a light-bending portion at its perimeter; the rear body section comprises an enclosure formed by the back side of the light-absorbing structure and walls of the rear body section, the two or more light sensors are positioned symmetrically on the flat board in relation to the light source position, and the light-bending portion is configured to bend a portion of the emitted light away from the light sensors and onto the inner surface of the enclosure such that the light is diffused, absorbed and/or reflected of before reaching the light sensors with reduced intensity. The implementations above may be advantageous in systems with various light intensity of the LED-s and their color and sensor specifications .

In a further implementation of the optical system according to the first aspect, a portion of the inner surface of the enclosure is covered with reflective material .

In a further implementation of the optical system according to the first aspect, the controller is configured to adjust the intensity of light emitted by the light source based on the light intensity readings received from the two or more light sensors. Adjustments to the intensity of light based on the readings has an effect of maintaining brightness and uniformity of light that exits the frontal optical arrangement throughout the lifetime of the LED-based railway signal.

In a further implementation of the optical system according to the first aspect, the rear lens comprises a combination of pins corresponding to a set of parameters of the rear lens, the flat board comprises a combination of holes corresponding to a set of parameters of the light source, and the pins and holes are configured to match only in one or more predetermined combinations, in which the sets of parameters of the rear lens and the light source match. This implementation has an effect of preventing incorrect installation or change of non-matching components. The parameters may include, for example, color or intensity of the light source, as well as others.

In a further implementation of the optical system according to the first aspect, converging frontal lens arrangement comprises a converging Fresnel-type lens with an overlaid structure and a smooth outer surface.

In a further implementation of the optical system according to the first aspect, converging frontal lens arrangement comprises two or more lenses, and at least one of the two or more lenses comprises dimming material. This allows to reduce brightness when needed. In a further implementation of the optical system according to the first aspect, the optical system of any of the previous implementations has a modular structure, wherein the frontal body section and the rear body section are detachable from each other. Modular system may be easier to maintain, repair and transport.

According to a second aspect, a lens for a railway signal based on light-emitting diodes is provided. The lens comprises: a light focusing element configured to collect, mix and focus or spread the light emitted by the light-emitting diodes; and a base portion having an elliptic or circular outer perimeter with a cut-out portion under a horizontal line below its center, wherein the base portion comprises a light-bending portion at the perimeter of the base portion. This lens may be suitable for various railway signals where low phantom light is a requirement. The lens may be used as a rear lens according to the first aspect. In an implementation of the lens according to the second aspect, the lens is shaped as a light collecting dome comprising a cut-out under a substantially horizontal line below its center, wherein with the dome has a facetted surface structure. In an implementation of the lens according to the second aspect, the lens has a round or elliptical shape comprising a cut-out under a substantially horizontal line below its center, and comprises a grid of domes configured to spread light passed through the lens.

In an implementation of the lens according to the second aspect, the lens has a round or elliptical shape comprising a cut-out under a substantially horizontal line below its center, and comprises a superposed cylindrical structure.

In an implementation of the lens according to the second aspect, the light-bending portion is configured to pass a portion of light emitted by the light-emitting diodes directly outwards. The light can be then picked up for example by light sensors. In an implementation of the lens according to the second aspect, the light-bending portion comprises a prism that bends a portion of the emitted light to a predetermined degree upward from or downward to the lens plane. Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings. DESCRIPTION OF THE DRAWINGS

The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein:

Fig. 1A is a schematic cross-section view of an optical system according to an embodiment,

Fig. IB is a schematic cross-section view of an optical system with a conical torse element;

Fig. 2a illustrates a rear lens with a facetted dome; Fig. 2b illustrates a rear lens with a grid of domes; Fig. 2c illustrates a rear lens with a superposed cylindrical structure;

Fig. 3 shows a light-absorbing structure shaped as a conical torse, and its cross-section;

Fig. 4a is a schematic cross-section of the area around the rear lens with a light-bending portion and light sensors ;

Fig. 4b is a schematic cross-section of the area around the rear lens with a light-bending portion that does not provide the light directly onto the sensors; and

Fig. 5 shows a schematic example of several sensor positions .

Like references are used to designate like parts in the accompanying drawings .

DETAILED DESCRIPTION

The detailed description provided below in connection with the appended drawings is intended as a description of the embodiments and is not intended to represent the only forms in which the embodiment may be constructed or utilized. The same or equivalent functions and structures may be accomplished by different embodiments.

Improvements in railway signals are tied to the strict requirements of brightness of light, railway signal sizes, relevant colors, low phantom light etc. In the present invention, an improved optical system and lens for railway signals are presented, and the requirements are addressed systematically and structurally. Embodiments of the invention, as described with reference to the drawings below, include an optical system with a rear lens positioned close to the light sources to collect and mix the light from one or more LEDs, configured to provide appropriate color-dependent light intensity by collecting or spreading light from LEDs via the rear lens and directing it towards the frontal lens arrangement. The rear lens in some of the embodiments comprises a horizontal step below its center caused by a cut-out lens segment, and the rear lens with this cut-out is surrounded closely by a conical torse having a light absorbing structure, to reduce phantom light. The rear lens in some embodiments is used to pass light from the LEDs to light sensors through a light bending rear lens perimeter, either directly or indirectly over reflection surfaces. Light intensity measurements and adjustments based on these measurements can further help to improve operation and safety of the signaling system. Fig. 1A shows a vertical view of a signal according to an embodiment, in cross-section. The embodiments illustrated on Figs. 1A-1B are only examples and include optional features that are not necessary for the achievement of the technical result provided by the claimed invention. For example, it is clear to a skilled person that a LED-board is not necessary for the functioning of LEDs, however it illustrates one way that the light source can be implemented.

On Fig. 1A signal body 1 comprises a rear body section la, and a frontal body section lb attached to the rear body section la. The body sections can be adaptable to several diameters and customized mounting needs. The rear body section la comprises a flat LED-board 2 with

LEDs 3 which make up a light source, covered by a rear lens 4. Rear lens 4 may include indexing pins 6 reaching into holes 7 in the LED-board 2, which ensures that certain properties of rear lens 4 is and the type of LEDs 3 match, and secures a correct position. The rear body section la also includes a lens holder 8 which is an example of a light-absorbing structure surrounding the rear lens 4 and protecting the LED-board 2. The frontal body section lb comprises an opening 10, which is normally circular in railway signals. The frontal lens arrangement 11 is provided in the opening 10. The frontal lens arrangement 11, illustrated in Figs 1A-1B as a Fresnel-type lens, collects the light 12a exiting from the rear lens 4 of the light source and refracts it to a substantially parallel beam 12b in an axial direction, addressed as optical axis 13, and possibly some peripheral light to the side and below, depending on the requirements. The frontal body section lb comprises a casing connecting the frontal lens arrangement 11 to the rear body section la, and the base wall of that casing may have a centered hole surrounding the light-absorbing structure in the lens holder 8 and protect the light source and electronics against environment and light ingress. In an embodiment, the inner surfaces of the casing are painted in black mat color and/or have a light absorbing structure as well. The frontal body section lb can be adapted to various requirements such as different signal diameters, different mounting devices and different signal lengths, but can also be made as one piece with the rear body la.

Frontal lens arrangement 11 is a converging arrangement and may be only one combined lens as shown in Figs. 1A- 1B, or an assembly of two or even more lenses, constituting a modular optical system providing several standards and light distributions, for example depending on track curves or train velocity. In an embodiment, the frontal lens arrangement can be of high surface precision and polishing quality to create a condensed focal point F near to the LEDs 3 and rear lens 4, to create the substantial parallel beam 12b with low tolerances. The rear lens 4 provides a necessary amount of light by sampling or spreading light, depending on the type of LEDs, color and LED current, and blurs positions of LEDs by a defined optical structure. To avoid unwanted reflections and phantom light, sunlight should not hit the rear lens 4. To provide clear visibility of the signal, in an embodiment all interior walls of the frontal body lb and lens holder 8 can have black mat surfaces because of the material, paint or/and surface structure used, to suppress any straylight generated by optical or lit surfaces. If sunlight 14b is falling onto the frontal optics, in most cases it would be falling from at least a small angle above the horizontal direction. According to optical laws the almost parallel sunlight beams 14b are focused by the frontal lens arrangement 11 in a small area below the LEDs 3, creating a virtual hot spot H. It is named "hot spot" because the sunlight also contains radiation heat, and "virtual" because sunlight would be focused in a spot at the focal length of the frontal lens arrangement 11, but in fact it does not reach the hot spot. Sunlight and radiation are absorbed before reaching this virtual hot spot H by the light-absorbing surfaces in this enclosure. According to phenomena described by Fresnel formulas, a small part of sunlight 14b is reflected at the surfaces of frontal optics 11 and creating a reflex phantom light 14c. These surfaces are usually curved and therefore spread the light over a wide area to minimize disturbances in axial direction. Reflections also occur on other optical surfaces inside the frontal lens arrangement 11 (not shown) and on all other lit surfaces, and these incidental reflections are referred to as straylight or flare, and contribute to a false phantom light that can be seen from outside the railway signal by an observer, for example an engine driver .

If some focused sunlight 14a still ends up touching the rear lens 4, a part of the sunlight can also fall onto the LED 3 itself and may be reflected from it using the same light path as the active light 12a, 12b and causing backlighting, also referred to as true phantom light. The false phantom light and the true phantom light together form the phantom light that must be limited in intensity and color influence according to certain requirements .

To prevent sun light from entering the rear lens 4, a horizontal segment is cut-off at its lower circumference, building a step 15. This has minimal impact on active light, however provides a technical effect of reducing phantom light by increasing absorption space for, and area of the hot spot H.

In some instances, active light and phantom light caused by the sun reflection can occur at the same time, passing the lenses without influencing each other. In this case the color of the light must be clearly recognizable when active light is switched on, as opposed to the color of phantom light when the active light is switched off, which can only be achieved if the phantom light is at a low level. Fig. IB is a cross-section of another embodiment wherein the rear body section la of the optical system comprises a light-absorbing conical torse 8a surrounding the rear lens 4 and exiting light 12a and protecting the LED- board 2. The rear body section also comprises a controller 20 and light sensors 5a, 5b outside the rear lens 4. Fig. IB clearly shows that the hot spot H is located behind the inner wall of the conical torse 8a, so the radiated area of the cone is bigger and therefore causes less heat in the light-absorbing material. The triangular light-absorbing structure 17 may support heat resistance by increasing the cone surface as well.

In an embodiment, a lens holder 8 can be mounted into the rear body section la, pressing the rear lens 4 onto the LED-board 2 and via a thermal elastic foil 9a against a plane 9b of the controller body la, to have good thermal contact. The light sensors 5a, 5b are configured to measure the intensity of light emitted by the LEDs 3 at a predetermined location in the rear body section la, and to provide light intensity readings to the controller 20. At the same time the light-absorbing structure 8 is configured to prevent light coming from the direction of the frontal lens arrangement from reaching the light sensors 5a, 5b. The use of light sensors 5a, 5b becomes more apparent from the embodiment shown in Figs. 4a-4b and 5.

Figs. 2a-2c show variants of rear lenses 4 according to embodiments. All of them include the cut-out 15 under a horizontal line below their centers which provides the effect of reduce phantom light. The example embodiments of rear lenses 4 shown on Figs. 2a-2c also comprise pins 6 at certain positions round the perimeter 16 to secure a correct combination with a corresponding LED-board 2. Some of these variants of rear lenses 4 can perform a mixing of light emitted by different LEDs, for example to allow emergency operation for a short period if one of the LEDs has failed. Structures of these variants can be geometrically predefined, optimized and have polished surfaces for high efficiency, to ensure that the light passed through them hits the frontal lens arrangement 11 in an even manner, and to minimize losses into black absorbing frontal body lb.

Fig. 2a shows a condensing rear lens 4 for maximum light sampling. The lens dome is covered with plain facettes 4a, working as structure instead of a common smooth lens dome. For optimal efficiency the facetted dome also has an oval shape. Fig. 2b shows a spreading rear lens 4 for reduced brightness. By using a grid of domes 4b the light is mixed and spread to surrounding black surfaces. A spreading lens refers to a lens with geometrically defined structure providing a pre-defined light distribution. This rear lens 4 may be beneficial with bright LED colors that cannot be made darker otherwise because of a specified minimum LED-current. This structure is designed for intentional losses in light intensity, but at the same time evenly lit frontal lens arrangement 11.

Fig. 2c shows a condensing rear lens 4 with a superposed cylindrical structure 4c for horizontal spreading, to get a better horizontal mixing of two LEDs in a row and nearly no vertical spreading.

Fig. 3 shows the conical torse 8a of a lens holder 8, or of a light-absorbing structure in other embodiments; and a cross-section of the triangular ribs 17. The ribs 17 may be positioned radially along the inner wall of the conic torse, with a triangular shape and an acute angle pointing upward from the base of the triangle. Surfaces can be black mat and form a light-trap, meaning that light rays coming from any direction are absorbed and partly reflected at least twice within this structure. Any straylight created by minor reflections is absorbed or reflected again due to the structure of the ribs 17. In other embodiments, triangular ribs 17 can also be applied to every light-absorbing inner surface of the frontal body lb, surrounding the conical torse 8a, to reduce the level of internal straylight.

In one embodiment, shown also on Fig. 3, the smaller opening of the conical torse 8a surrounds the rear lens 4 at the perimeter, including the cut-out 15. The conical torse 8a angle is defined based on the angle of exiting light 12a. The conical torse provides a structure wherein no surface around the rear lens 4 is perpendicular to sun rays in the area of the hot spot H, which reduces local heating. So this geometry allows to use a heat- resistant plastics material for the lens holder 8 and conical torse 8a, advantageous also for electric isolation and for fixing the rear lens 4, the LED-board 2 and other components like foils 9a together.

The area around the conical torse 8a can be reached by the sunlight, but due to optical properties of the frontal lens arrangement would not be focused anymore, so there is minimal danger of higher heat radiation and weakening. This area may also be covered by the frontal body section lb, for example made of aluminum.

In addition to optical properties of system and lens for railroad signals, in further embodiments there may be additional internal means for supervising functionality, brightness compensation and failure detection. These means can include two optical sensors 5a, 5b to measure the light intensity of the LEDs, supported by an electronic controller 20 in two-channel safety architecture, including analysis and compensation modules. If an LED fails, a decision can be made to shut down the signal, or to increase the current for the remaining LED and report a warning, for example by switching the signal from the primary to the secondary circuit, imitating incandescent signals with a two- filament bulb. Fig. 4a and 4b are cross sections of the rear lens 4, conical torse 8a and LED-board 2, according to an embodiment, showing how the sensors are lit, depending on sensitivity and working range of sensors 5a, 5b. The sensors are mounted onto the LED-board 2, outside the rear lens and covered by the lens holder 8, conical torse 8a and conical torse wall 8b, forming an enclosure 8c together with the LED-board 2 against any disturbing light from outside the signal. Fig. 4a shows a rear lens 4 with its perimeter 16 configured as a prism for the light from LEDs exiting aside missing the rear lens structure, and bending it towards the active surface of sensors 5a, 5b. An LED- light can be substantially brighter than the measuring range of a brightness sensor. Using the light coming from aside and hitting the sensors at a distance at a very flat angle may reduce light intensity to a useful range . Fig. 4b shows a rear lens 4 with a perimeter 16 configured as a prism for the light from LEDs exiting aside missing the rear lens structure, and bending it away from the sensors, falling onto the surrounding wall 8b and backside of the conical torse 8a and finally hitting the sensors 5a, 5b with strongly reduced intensity. Absorption of black materials is less than 100%, so the light is reflected and spread around in this enclosure 8c, but with heavy losses in intensity. This absorbing material reduces light intensity on the sensors by tens of magnitude. In other embodiments, light intensity on the sensors can be adapted to a useful level by additional walls and surfaces 8d in this enclosure 8c .

Fig. 5 shows a scheme of sensor positions in relation to LED-positions . The two LEDs 3a, 3b according to this embodiment are positioned in a horizontal row at minimum distance in the center of the rear lens 4, having a border 16 like for example in Fig. 4a.

If the sensors 5a, 5b are mounted left and right ("L" and "R") , every sensor is configured to check its preferred LED 3a or 3b. If a LED fails, one sensor's level goes nearly down to zero. But this may also be a sensor failure.

If sensors are mounted up and down ("U" and "D") , every sensor is configured to check both LEDs together. If one LED fails, both sensors will report half intensity. In this case it may not possible to find out which LED failed. If only one sensor reports failing, LEDs may be o . k . If sensors are mounted symmetrically between left/right and up/down (for example "LD" and "RD") , it is possible to check and identify LED-functions as well as sensor- functions . LED-current can be regulated by pulse width modulation. If sunlight is falling onto the LEDs and reflected towards the sensors this is recognized as an overlapping constant light level and considered in the controller 20. If the rear lens 4 has a border like Fig. 4b, spreading the light over the whole enclosure 8c, both sensors will report sum of LED-brightness , regardless to its positions. In other embodiments, more than two LEDs are used in the signal, and also more than two sensors. The sensors will react differently, depending on position of LEDs and sensors, which has to be considered and customized in the controller 20.

In yet another embodiment, any of the lenses can be used with neutral dimming material or grey filters to reduce brightness. This has no color effect on colored or white light, because light intensity is reduced for the same factor at every wavelength, but it can be beneficial to further reduce phantom light, because sunlight must pass grey materials twice, the active light only once and so phantom light is reduced more than the active light. In addition, radiation heat can partly be transferred to the lens comprising dimming material, and so it reduced at the conical torse 8a.

Proportions in the drawings may be exaggerated or altered for illustrative purposes, and should not be interpreted as the only accurate visual representation of the structures and devices shown. Any range or device value given herein may be extended or altered without losing the effect sought. Also any embodiment may be combined with another embodiment unless explicitly disallowed.

Although the subject matter has been described in language specific to structural features and/or functions, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or functions described above. Rather, the specific features and functions described above are disclosed as embodiments of implementing the claims and other equivalent features and functions are intended to be within the scope of the claims.

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items. The term 'and/or' may be used to indicate that one or more of the cases it connects may occur. Both, or more, connected cases may occur, or only either one of the connected cases may occur. Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought .

The term 'comprising' is used herein to mean including the elements, structures or modules identified, but that such elements, structures or modules do not comprise an exclusive list and a method or apparatus may contain additional elements, structures or modules.

It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, embodiments and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this specification.