The invention relates to an obstacle hght optic, for example for marking a tower, such as a tower of a wind turbine.

For marking a tower as an obstacle easily discernible by aviation and, if the tower is located offshore, by ships, warning lights are mounted to the tower. It is for example known to mount a warning light at the outside of the wind turbine tower.

A problem associated to such lights is that installation and maintenance is costly, because reaching locations at the outside of the tower, especially location for obstruction lighting for aviation that are high above the ground or sea level, is cumbersome and requires highly

specialized high altitude climbers and special climbing equipment. In offshore situations high altitude work is often impossible in view of weather circumstances, or at least very expensive.

Additionally, when such a warning light fails, it is time consuming and costly to send a worker up to the tower wall to repair and/or replace the failed warning hght.

Various attempts have been made to alleviate this problem. One approach is mounting the light fixtures inside or from the inside of the tower.

For example it is known to install a light source inside the tower, and then, via a fiber optic cable going through a hole in the tower wall, to transmit the light to a light optic outside of the tower. However, obtaining a required light emitting pattern is difficult to due to the random light distribution exiting from the fiber optic cable. Also, it is known to install a rod-shaped light fixture from inside the tower through holes or other openings in the tower. However this requires relatively large openings to be made in the tower, which may compromise the strength of the tower or may require reinforcements or other measures to compensate therefor. Also, it turned out that aligning of the light fixture was rather burdensome due to the installation from the inside, as during installation it is difficult to see what happens with the light at the outside of the tower.

Therefore, there is a need for an obstacle light for marking a tower that obviates at least one of the above mentioned disadvantages.

Thereto, the invention provides for an obstacle light optic according to claim 1.

By providing an optic with a first reflecting part having a surface of revolution and a second reflecting part having a surface of revolution with respect to a first and a second revolution axis respectively, the light emitted by the light emitting element can be optimally directed towards the exit surface such that a side-emitting optic is obtained. As now almost all hght is directed towards the exit surface, i.e. towards a single side of the optic, more efficient use is made of the light emitted by the light emitting element. This is advantageous for marking e.g. towers. Part of the light emitting is now being used for the light output of the optic and, additionally, light rays impinging on the tower wall and causing a diffused light spot on the tower wall is now being avoided. Such a diffused light spot on the tower wall was experienced annoying by pilots, captains etc. Also, since approximately all hght emitted by the light emitting element is now being used for light output of the light optic, a same or similar hght output or hght intensity can be obtained with a light emitting element of a lower intensity than the prior art omnidirectional optics.

Typically, such an obstacle light optic is arranged to emit light over a sector with an exit angle in a plane containing the exit axis and transverse to the entrance axis. This is the so-called horizontal beam spread. This horizontal beam spread, or exit angle, is preferably between approximately 30 degrees and approximately 200 degrees, such that hght is emitted to a single side of the optic only. Also, the obstacle light optic is preferably arranged to emit light over a relatively small angle in a plane containing the entrance axis and the exit axis, this is the so-called vertical beam spread. This vertical beam spread is usually defined by regulations, and can be between approximately 0, 1 degrees and approximately 15 degrees. Due to the efficiency of the light optic, the hght optic can be very compact, between approximately 5 mm and approximately 50 mm in height. This makes the configuration easy to handle and install.

By providing the first reflecting surface and the second reflecting surface as a surface of revolution, the light can be directed towards the exit surface within the predefined horizontal and/or vertical beam spread. The first revolution axis and/or the second revolution axis can be coincident with the entrance axis, but can also be parallel to the entrance axis.

Advantageously, the first and/or the second revolution axis are parallel to the entrance axis, as this improves the compact design, but depending on the desired light output pattern, the first and/or second revolution axis may be shifted somewhat with respect to the entrance axis.

Advantageously, the first reflecting part and the second reflecting part are a part of a cone shaped body, formed by a straight line rotated around the first revolution axis and the second revolution axis respectively. This provides for an efficient design, which can be easily manufactured.

The obstacle light optic is thus configured to emit hght

substantially to a single side of the optic only. Considering a plane containing the entrance axis and transverse to the exit axis, one side of the plane may be considered a first side in which the first reflecting part is substantially positioned, and the other side of the plane may be considered a second side in which the second reflecting part is substantially positioned. Of course, such a plane divides the optic in two parts of 180 degrees, while the second reflecting part may be between approximately 30 degrees and approximately 200 degrees. The second reflecting part has advantageously about the same or similar angle as the exit angle, and thus of the exit surface. The first reflecting part then has an angle of 360 degrees minus the angle of the second reflecting part, wherein the angle is measured in a so- called horizontal plane, containing the exit axis and transverse to the entrance axis.

The second reflecting part may, in an embodiment, be substantially inverted with respect to the first reflecting part with respect to the entrance axis. This can be obtained by two subsequently symmetric operations of the first reflecting surface. For example, firstly an intermediate symmetry surface of the first reflecting surface with respect to a plane containing the entrance axis and transverse to the exit axis can be provided. Then, secondly, from this intermediate symmetry surface further a symmetry surface can be obtained with respect to a plane containing the exit axis and transverse to the entrance axis. This further symmetry surface may then substantially correspond with the second reflecting surface. As such, the first and the second reflecting surface may form part of a diabolo-like body. Of course, the angle of the first reflecting surface with respect to the entrance axis may be different from the angle of the second reflecting surface with respect to the entrance axis. Also, the first axis of revolution may be shifted with respect to the second axis of revolution, so the second reflecting surface may not be exactly obtained by the previously described symmetry-operations, but may merely correspond as such.

Advantageously, the hght optic is a sohd body, that may be obtained by injection moulding. Due to the manufacturing process, it may be that the exit surface, in particular a skirt forming the exit surface, for example may have a slight inclination with respect to the entrance axis of about 0, 1 to about 3 degrees, depending on manufacturing tolerances.

Advantageously, the exit surface is substantially shaped as a bent surface with respect to the entrance axis, e.g. substantially cylindrically shaped, or substantially oval shaped, etc. and or the exit surface is provided with at least one lens. The exit surface can be obtained in various ways, e.g. s a revolution surface by revolving a line, which can be straight or curved or wave shaped, or any other shape, around the entrance axis. However the exit surface can also be shaped around the entrance axis, when seen in top view, as part of an oval shaped. Many variants and combinations thereof are possible. Advantageously, the exit surface is provided on a skirt of the optic extending over at least the exit angle, and over at least a part of the height of the optic. In further embodiments, the exit surface may itself be provided with at least one lens, to further direct or colhmate the light to obtain a predefined light output. The exit surface may be substantially shaped as a bent surface with respect to the entrance axis. Alternatively or additionally, the exit surface may even not be a surface of revolution, but may be obtained by other ways, e.g. may be segmented or partly polygonal etc. By further shaping the exit surface, e.g. with lenses, the light output can be better directed or distributed, or undesired light rays can be corrected or redirected. This may improve the total light output. Also, by further providing the exit surface with e.g. at least one lens, larger, in particular larger negative angles in a vertical spread can be obtained, so a wider vertical spread may be obtained.

The exit surface may be a substantially cylindrical surface extending over an azimuthal, or horizontal, angle substantially

corresponding with the exit angle, which gives a compact design. Further, the optic may be provided with a skirt, substantially cylindrical extending over approximately the exit angle, and extending over approximately the height of the optic. The exit surface may thus be provided on the skirt of the optic, preferably at a top part of the skirt. The bottom part of the skirt may then be provided may then be used for mechanical purposes, such as for mounting or stacking.

Advantageously, the obstacle hght optic is stackable onto a further obstacle hght optic. For example, mounting elements can be provided that are arranged for cooperation with corresponding mounting elements on the further obstacle light optic. The mounting elements can be provided e.g. on the skirt of the optic, or may be provided on a mounting board on which an optic can be mounted. Many variants are possible. Due to the compact design of the light optic, stacking multiple hght optics, still gives a compact design, and allows to provide for, for example, a safe-life optic system or for an optic system comprising an optic with a light emitting element emitting visible light and an optic with a light emitting element emitting infrared hght, or other variants.

The invention further relates to an obstacle light system

comprising at least two obstacle light optics.

Further advantageous embodiments are set forth in the dependent claims.

The invention will further be elucidated with reference to a drawing. In the drawing:

Figure la shows a schematic perspective view of an embodiment of a light optic with an exit angle of approximately 180 degrees;

Figure lb shows a schematic side view of the embodiment of figure la;

Figure lc shows a schematic front view of the embodiment of figure la;

Figure 2a shows a schematic perspective view of another

embodiment of a light optic with an exit angle of approximately 180 degrees;

Figure 2b shows a schematic side view of the embodiment of figure

2a;

Figure 3 shows a schematic perspective view of an embodiment of a light optic with an exit angle of approximately 90 degrees

Figure 4 shows a system of two hght optics wherein one light optic is stacked on another light optic;

Figure 5 shows a schematic side view of another embodiment of a hght optic with an exit angle of approximately 180 degrees; Figure 6a shows a schematic top view of hght rays emitted from the light optic;

Figure 6b shows a schematic side view of light rays emitted from the hght optic;

Figures 7a, 7b and 7c show a graphical representation of the exit angle of the light optic;

Figure 8 shows a schematic side view of a further embodiment of the light optic.

It is to be noted that the figures are given by way of exemplary embodiments only. Corresponding elements are designated with

corresponding reference numbers.

Figure la shows a schematic perspective view of an obstacle hght optic 1. The optic 1 comprises a light transmitting element 2 having an entrance surface 3 with an entrance axis A and an exit surface 4 with an exit axis B. The exit axis B is oriented substantially transverse with respect to the entrance axis A. The exit surface 4 allows to exit light to a single side of the optic only 1 in a direction substantially transverse to the entrance axis A over an exit angle alpha. The entrance surface 3 defines a recess 5 in the light transmitting element 2 in which a light emitting element 6 can be received. The light emitting element 6 typically is a LED. The recess 5 is sized to receive a single light emitting element 6. The light emitting element 6 is arranged in the recess 5 such that a light emitting surface 7 faces the entrance surface 3 of the light transmitting element 2. The light emitting element 6 typically emits light approximately hemispherical in a main light emitting direction along the entrance axis A.

The light transmitting element 2 comprises a colhmating part 8, a first reflecting part 9 and a second reflecting part 10. Considering a plane P containing the entrance axis A and transverse to the exit axis B, this plane P basically defines two sides, a first side 11 and a second side 12. The second side 12 contains the exit surface 4, and the first side 11 is opposite. The first reflecting part 9 is substantially positioned at the first side 11 and the second reflecting part 10 is substantially positioned at the second side 12. The first reflecting part 9 and the second reflecting part 10 are, when seen in a direction along the entrance axis A, positioned above the collimating part 8. The light emitted by the hght emitting element 6 will pass through the collimating part 8 before entering the first reflecting part 9 and/or the second reflecting part 10. The second reflecting part 10 is also situated more above the colhmating part 8 than the first reflecting part 9.

The first reflecting part 9 and the second reflecting part 10 are arranged to reflect light towards the exit surface 4. The first reflecting part 9 has a first reflecting surface 13 and the second reflecting part 10 has a second reflecting surface 14. The first and the second reflecting surface 13, 14 are surfaces of revolution obtained by rotating a line with respect to a first revolution axis Rl and a second revolution axis R2 respectively around an angle Betal and Beta2 respectively. The first revolution axis Rl and the second revolution axis R2 are preferably coincident with the entrance axis A to obtain a more optimal optical performance, as shown in the embodiment of figures 2a, 2b. Alternatively, the first revolution axis Rl and the second revolution axis R2 are parallel to the entrance axis A, as in this example shown in figures 1 and 3.

When the revolution axes Rl and R2 are coincident with the entrance axis A, this provides for a more optimally optical output of the light optic. The reflecting surfaces 13 and 14 then have a common 'starting point' where they intersect the entrance axis. This even more gives a shape of a 'diabolo' or a 'sandglass'. Also for manufacturing, coinciding revolution axes with the entrance axis makes it easier to loosen the body from the mould. In the embodiment shown in figures 2a and 2b, the angles Betal and Beta2 are 45 degrees, but here too, the angles Betal and Beta2 can differ and vary between approximately 30 degrees and approximately 60 degrees, depending on the desired light output pattern. Also, the skirt 16 on which the exit surface 4 is provided has here a lower part 16b, on which mounting element 17b is provided and an upper part 16a comprising the exit surface 4. Both parts may be shaped differently, for example the upper part 16a can be cylindrically shaped, and the lower part may be conical shaped, and many variants thereof may be possible. It is advantageous that at least the lower part is somewhat conically shaped to improve loosening of the body from the mould after injection moulding. The embodiment of figure 8 illustrates that the exit surface 4 may be shaped further, e.g. with at least one additional lens 20. As such the light output pattern can be even more directed or shaped to the desired light output pattern. Then, the exit surface may even not be a surface of revolution, but may be obtained by other ways, e.g. may be segmented or partly polygonal etc.

The line to be rotated around the first revolution axis Rl and/or around the second revolution axis R2 can be a straight line, or a parabolic line, or any other shaped line to obtain a reflecting surface shaped to reflect the light towards the exit surface 4.

The first reflecting part 9 and the second reflecting part 10 thus may form a part of a cone shaped body. The line to be rotated around the first revolution axis Rl and/or around the second revolution axis R2 is preferably inclined with respect to the respective revolution axes around an angle Betal and Beta2 respectively, and thus with respect to the entrance axis A, about an angle between approximately 30 degrees and

approximately 60 degrees. For example, the angle Betal of the first reflecting surface 13 with respect to the entrance axis A may be about 42 degrees, and the angle Beta2 of the second reflecting surface 14 with respect to the entrance axis A may be about 42 degrees. In another embodiment, the angle of the first and the second reflecting surface 13, 14 may be about 45 degrees. Many variants are possible.

The exit surface 4 is substantially cylindrically shaped with respect to the entrance axis A and extends over approximately the exit angle alpha. The substantially cylindrically exit surface 4 may be a part of a cylinder having the entrance axis A as central axis. However, the exit surface 4 may be inclined somewhat as well, for example for manufacturing reasons, so it may well be that the exit surface 4 is not exactly cylindrically, but slightly conical e.g. over an angle of approximately 0, 1 degrees to approximately 3 degrees. This is advantageous when manufacturing the light transmitting element 2 by means of injection moulding for loosening the light

transmitting element 2 from the mould.

The exit surface 4 preferably extends over an azimuthal angle gamma of about the exit angle alpha, for reasons of manufacturing etc. the azimuthal angle gamma over which the exit surface 4 extends may be somewhat larger than the exit angle alpha. Preferably, the second reflecting part 10 extends over about the same azimuthal angle gamma,

approximately the exit angle alpha. The first reflecting part 9 thus extends over an azimuthal angle of 360 degrees minus the azimuthal angle gamma of the second reflecting part 10. In the embodiment of figures la - lc, the exit angle alpha is approximately 180 degrees. Figure 3 shows an

embodiment similar to the embodiment of figures la - lc, but with an exit angle alpha of approximately 90 degrees. As such, the light output of the optic 1 is at one side of the optic 1 only. When using the hght optic 1 for marking a tower, the light is outputted to a side towards the environment as seen from the tower. There is thus no or minimal hght directed to the tower itself, which is advantageous to optimally use the light emitted by the hght emitting element. Alternatively, an omnidirectional light system can be obtained by using two optics as in figures la - lc or by using four optics as shown in the embodiment of figure 3.

By arranging the collimating part 8 for collimating the light entering the entrance surface 3 towards the first reflecting surface 13 and towards the second reflecting surface 14, most of the light emitted by the light emitting element 6 can be used, and an efficient hght optic 1 can be obtained. Also, by arranging the first reflecting part 9 and the second reflecting part 10 such that light is directed towards the exit surface 4, almost all light is reflected towards the exit surface 4 as light output of the optic. This provides for a more efficient light optic in which optimal use is made from the light emitted by the hght emitting element. Also, a very compact light optic 1 can be obtained. Typically, a height H of the light optic 1 may be between approximately 5 mm and approximately 50 mm, for example around 20 mm. So, a very small warning hght can be obtained which provides for sufficient hght intensity for marking the tower.

The collimating part 8 advantageously comprises a surface of revolution 15 with the entrance axis A as rotation axis. The surface of revolution 15 of the collimating part 8 is obtained by revolving a line around the entrance axis A, wherein the line typically is a parabolic line to optimally collimate the light towards the first reflecting surface 13 and towards the second reflecting surface 14. Light emitted by the light emitting element 6 is reflected and collimated by the surface of revolution 15.

In the side view of figure lb can be seen that the first reflecting part 9 is substantially at the first side 11 and the second reflecting part 10 is substantially at the second side 12. The exit surface 4 is at the second side 12. The second reflecting part 10 can be considered as being inverted from the first reflecting part 9 with respect to the entrance axis A. The first and second reflecting surfaces 13, 14 thus form somewhat surfaces of a so-called diabolo. In fact, when mirroring the volume forming the first reflecting part 9 with respect to a plane transverse to the first reflecting surface and then inverting this mirrored volume - material becomes air and air becomes material - the second reflecting part 14 is more or less obtained. As such, the second reflecting part 10 may be considered "inverted" with respect to the first reflecting part 9.

The exit surface 4 preferably extends over an azimuthal angle of approximately the exit angle, and preferably extends over an height sufficiently to allow light reflected by the first reflecting surface 13 and by the second reflecting surface 14 to exit the optic. This is for example shown in figure 5. The height Hx is about the height of the first reflecting part 9 and of the second reflecting part 10. In an embodiment, e.g. the embodiment of figures la - lc, the light transmitting element 2 may be provided with a skirt 16 extending over the height H of the optic 1. An upper side of the skirt 16 comprises the exit surface 4, while a lower side of the skirt 16 may have a mechanical function e.g. as support, for mounting or provided with

mounting elements, or may be provided for improved manufacturing of the hght transmitting element 2. The hght transmitting element 2 is preferably a solid volume made as a single piece for example by injection moulding. For easy removal of the moulded piece from the mould, some surfaces may have a slight inclination.

In this embodiment, shown in figures la - lc the first reflecting surface 13 ends at end 13a while the second reflecting surfaced 14 begins at beginning 14a. The end 13a and the beginning 14a are at some distance from each other. However, in other embodiments, the end 13a and the beginning 14a may coincide, such that the second reflecting surface 14 may smoothly continue from the first reflecting surface 13.

In figure 3 can be seen that the skirt 16 of the light transmitting element 2 is provided with mounting elements 17. At a top side 16a of the skirt 16, mounting elements 17a are provided and at a bottom side 16b of the skirt 16 mounting elements 17b are provided. The mounting elements 17a, 17b may be embodied as a pin and a hole or as a rib and a groove or as any other means. By providing the mounting elements 17a, 17b, the light transmitting elements 2 can easily be stacked on each other, as shown in figure 4. By stacking the optics 1, a compact system can be obtained from which for example one optic is provided with a visible hght emitting element and another optic may be provided with an infrared hght emitting element, or another optic may be provided with a white light emitting element or with a red light emitting element, etc. Also, by stacldng optics on each other, a system may be provided that is safe-life, comprising sufficient redundancy such that, in case of failure of one light optic, another light optic can take over the function. This is advantageous for service, maintenance and thus costs. In fact, by providing such a safe-life system, this means that, in case of failure, another light optic can automatically, or by a manual switch at the inside of the turbine tower, take over the function of emitting light in a predefined pattern. In particular for offshore installations, this is

advantageous as expensive repairs can be avoided. Also, due to the limited and compact size of the light optic 1, a system of stacked light optics 1 remains relatively compact.

Alternatively to providing the mounting elements 17 onto the skirt 16 of the light transmitting element 2, the mounting elements 17 may be provided on a mounting board 18, as shown in figure 5. The mounting board 18 is preferably provided for mounting the light emitting element 6 thereon. The mounting board 18 may e.g. be a printed circuit board, or a plate comprising electronic components. The mounting board 18 may also be used as structural interface for mounting an optic 1 onto a further optic 1 and thus to stack optics.

Figures 6a and 6b show a light emitting pattern of a light optic 1 over an exit angle alpha of approximately 200 degrees. From the top view of figure 6a it can be seen that light is emitted to a single side of the optic 1 only, so that a side-emitting optic 1 is obtained. In figure 6b are light rays shown that are emitted from the light emitting element 6 schematically represented. It can be seen that the hght rays are first collimated by the collimating part 8. A first bundle of light rays is reflected and collimated towards the first reflecting surface 13, and a second bundle of light rays is reflected and collimated towards the second reflecting surface 14. The first reflecting surface 13 then directs the light towards the exit surface 4 and the second reflecting surface 14 directs the light towards the exit surface 4. This schematic representation shows that almost all light rays are directed towards the exit surface 4 and that there are minimal diffused light rays. This is advantageous for the use of the light optic for marking e.g. a tower. The light is preferably emitted with a relatively narrow vertical beam spread, typically between approximately 0,1 degrees and approximately 5 degrees, resulting in a relatively narrow beam in vertical direction, i.e. in direction along the entrance axis A. Further, the light is outputted in a light pattern with a predefined horizontal beam spread, i.e. the exit angle alpha, which is in this embodiment approximately 200 degrees. Examples of horizontal beam spread are given in figures 7a, 7b and 7c. Figure 7a gives an example of a horizontal beam spread of approximately 240 degrees, figure 7b gives an example of a horizontal beam spread of approximately 180 degrees and figure 7c gives an example of a beam spread of

approximately 140 degrees. Many variants are possible.

An obstacle light optic is provided having a collimating part, a first reflecting part and a second reflecting part. A light emitting element is provided that emits light towards the collimating part, wherein the collimating part reflects and collimates the emitted light towards the first reflecting part and the second reflecting part. The first reflecting part and the second reflecting part are configured to direct light from a light emitting element towards an exit surface at a single side of the optic only.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include

embodiments having combinations of all or some of the features described. It may be understood that the embodiments shown have the same or similar components, apart from where they are described as being different.

In the claims, any reference signs placed between parentheses shall not be construed as hmiting the claim. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage. Many variants will be apparent to the person skilled in the art. All variants are understood to be comprised within the scope of the invention defined in the following claims.