Description

The present invention relates to a signalling device for placement along a roadway, which signalling device comprises a housing for capturing light emitted by passing vehicles onto a photoluminescent surface disposed in the housing, which photoluminescent surface comprises a luminescent material, as well as a lens for directing the captured light to the photoluminescent surface.

Such signalling devices are generally known; they are used to emit light for some time after the luminescent material in the photoluminescent surface has been irradiated by a light source. Such signalling devices are used along public roads, for example, in particular along roadways of public roads where such signalling devices emit light for some time in dark surroundings after being irradiated by a light source of a vehicle passing on the roadway. Thus, active road marking for further vehicles on the roadway is provided for the period during which the luminescent material continues to emit light.

The presence of a lens in the housing of the signalling device causes the light captured to be directed to the luminescent material in the housing. In particular, a light beam as emitted by the headlights of a passing vehicle is converged to the photoluminescent material in the photoluminescent surface by a lens mounted in the housing.

However, such signalling devices have the drawback that the photoluminescent surface is effectively irradiated mainly at certain angles of incidence. When a vehicle on the roadway in line with the device radiates light on the device, the lens will focus the light onto the photoluminescent surface in such a manner that the photoluminescent surface will capture sufficient light for emitting an afterglow for some time after being irradiated. Since the device is irradiated with light from various positions of the vehicles on the roadway, however, the photoluminescent surface will optimally capture the light only from some of these positions.

Accordingly it is an object of the present invention to provide a device as described in the introduction which captures the light from passing vehicles on the roadway in a better way. This object is achieved by the present invention in that the photoluminescent surface lies in a curved plane. The vehicles on the road are not static, that is, they move forward on the road, past the signalling device. Because the signalling device, on the other hand, is static, different positions of the vehicles on the road lead to different image points on the photoluminescent surface. Prior art signalling devices have a straight photoluminescent surface. By using a curved photoluminescent surface, however, the focal point will be located at least substantially on the photoluminescent surface for several positions of the vehicles on the roadway.

The object of the present invention, according to a first aspect thereof, is thus achieved by providing a signalling device that employs an improved method of capturing the light irradiated thereon. More in particular, light is captured on the luminescent material from several positions of the light source on the roadway, as a result of which more electrons in the luminescent material are excited. This results in a larger number of electrons returning to a lower energy level, and thus the light intensity of the light emitted from the luminescent material will remain sufficient for performing a signalling function for next vehicles on the roadway.

JP 2004-144857 describes a retroreflection element for use as a visual guide in traffic. Said document is focused mainly on the retroreflection efficiency. Laterally incident light falls on the lens, which is shaped in the form of a hemisphere. The light is broken, so that it falls on a retroref lector on the opposite side of the hemisphere and is reflected substantially in the direction of incidence via the lens. A strip of a luminescent material extends under the flat bottom side of the lens, substantially parallel to the expected direction of incidence of light. Light from passing traffic will hardly irradiate said strip, if at all, however.

In another embodiment, the concave side or the convex side of the photoluminescent surface faces the lens, and in yet another embodiment the lens comprises a concave or a convex lens.

In yet another embodiment, the photoluminescent surface is curved, viewed in a transverse cross-section of the signalling device. Because the photoluminescent surface, which comprises luminescent material, is curved, it provides an improved photoluminescent effect of the material from several positions of the vehicles on the roadway. Since the headlights of the passing vehicles radiate light substantially transversely to the lens surface in a faraway position of the device, the effect of the luminescent material can be said to be efficient for this position. When the vehicles approach the device, however, the light will no longer be radiated transversely to the lens surface, because the device is static. The image point of the incident light for these positions thus no longer lies in the focal point, i.e. no longer on the luminescent surface, as a consequence of which the photoluminescent effect of the device will diminish. If the luminescent surface is curved, viewed in a cross- section of the device, this has the advantage that the focal point of the light emitted by the headlights will lie on or at least substantially on the photoluminescent surface for several positions of the passing vehicles, resulting in an improved effect over the various positions of the vehicles on the roadway.

In a next embodiment, the photoluminescent surface is curved so that the image point of light radiated through the lens by a vehicle will lie at least substantially on the photoluminescent surface during the entire period of the passage of the vehicle.

The various positions of a passing vehicle on the roadway form a continuous transition from a position some distance away from the device to a position near the device. The image point of the light radiated through the lens from the light source will lie at different positions in the device during the entire period of this transition. Because the surface provided with luminescent material of the device is curved so that the image point of the light from the passing vehicle lies on (or substantially on) the photoluminescent surface for at least substantially all positions on the roadway, an improved effect of the surface will be obtained for several, if not all, positions of the vehicle. This results in an improved effect of the device for several or all positions of the vehicle passing on the roadway.

In another embodiment, the focal point lies a short distance behind the photoluminescent surface, and in another embodiment the focal point lies a short distance before the photoluminescent surface. Put differently, in such an embodiment the distance from the centre of the lens to the various positions on the photoluminescent surface is essentially 1x, 1x or slightly more than 1x the focal distance. If the focal point lies before or behind the photoluminescent surface, the surface on which the electrons in the luminescent material are excited will be larger than in the case where the focal point lies exactly or substantially on the luminescent material. The result of this is that a larger area will be activated and that thus a larger area of the material will emit an afterglow as a result of photons being emitted.

In a more specific embodiment, the device is configured so that the distance from the lens to the material ranges between 1.2x and 2x or between 0.5x and 1x the focal distance. More in particular, it ranges from 1 .1x to 1.5x and from 0.7x to 1x.

The lenses that are used may be lenses which are concave or convex on one side or concave or convex on both sides, i.e. biconvex, biconcave, plane-convex or plane-concave, or concave-convex.

In another embodiment, the luminescent material comprises a phosphorescent material or a fluorescent material.

The luminescent material, in particular the photoluminescent material, is a material which absorbs photons. As a result of said absorption, the photons are re-emitted. This can be regarded as excitation to a higher energy level, with the return to a lower energy level being accompanied by the emission of photons. The duration of the afterglow or the re-emission of the photons will be in proportion , it can vary from a few nanoseconds to a few seconds, a few minutes or even longer periods. In a specific embodiment of photoluminescent material, a photon of a particular wavelength is absorbed in the material and an equivalent photon is directly emitted. No significant transition of internal energy between absorption and emission takes place in that case.

When a specific luminescent material, such as a fluorescent material, is used, with internal energy transition taking place prior to emission, photons can be absorbed which have a comparatively high energy level in relation to the emitted photons. Such a fluorescent material is very suitable for use in traffic devices in which the attention of traffic participants on a public road is drawn to specific information or in which the road is indicated by means of reflector posts/roadside posts. In such fluorescent material, shortwave blue light is converted into colours with a longer wavelength, so that they appear to actively emit light under certain circumstances.

Another special form of luminescent material is a phosphorescent material. Phosphorescent material will emit an afterglow for some time after being irradiated, usually as a result of the slow return of electrons excited by being irradiated with light. Since the return of the electrons to the ground state constitutes a forbidden transition, the period during which the material will emit an afterglow is usually longer than when a fluorescent material is used. In another embodiment, the device further comprises adjusting means designed for adjusting the distance between the photoluminescent surface and the lens.

The adjusting means make it possible to adjust the distance between the photoluminescent surface and the lens. In some situations it may be desirable to irradiate a larger area of the photoluminescent surface than in other situations. In some cases a longer afterglow period is desired, and in other situations it is desirable to provide a larger afterglow area. The adjusting means make it possible to adjust the distance between the lens and the photoluminescent surface by moving the photoluminescent surface further away from the lens, i.e. adjusting the position of the luminescent surface in the device, or by adjusting the position of the lens in the device. In another embodiment, a rear side of the housing of the device may be formed by the photoluminescent surface, whilst in a special embodiment the distance from the rear side relative to the housing is adjustable.

In a specific embodiment, the adjusting means can be set in fixed positions. Being able to set the photoluminescent surface in discrete positions has the advantage that a large number of devices can be simply adapted to each other in this way. If it is desirable for a particular roadway or for a particular part of a roadway to position the photoluminescent surface closer to the lens such that it lies at a short focal distance, all the devices in question can be easily placed in a specific position.

In another embodiment of the present invention, the housing comprises one or more side walls extending toward a rear wall, the inner side of which side walls is preferably reflective. Light that is radiated onto the housing by the headlights of passing vehicles on the roadway, which light is not directly converged on the photoluminescent surface by the lens, are reflected onto the photoluminescent surface yet by the reflective side walls. Consequently, the electrons of the luminescent material are excited by a larger number of photons of the light incident in the housing. In another embodiment, only one side wall consists of a reflective material or is lined with a reflective material. In said embodiment, the other side wall forms part of the curved photoluminescence surface. The device according to said embodiment is thus formed by a lens positioned at the front side of the housing, a photoluminescent surface positioned at the rear side of the housing, opposite the lens, which surface is curved so that it smoothly merges into one of the side walls, wherein the second side wall does not form part of the luminescent surface but is lined with or made of a reflective material.

A second embodiment of the invention is characterised by a signalling device for placement along a roadway, comprising a housing for capturing, at a front side thereof, light emitted by passing vehicles onto a photoluminescent surface disposed in the housing, which photoluminescent surface comprises a luminescent material, as well as a converging lens for directing the captured light to the photoluminescent surface, which lens comprises a multitude of lenses.

In an embodiment of a signalling device in which the light incident in the housing is converged to the photoluminescence surface by one lens, the light reflected from the luminescent material will also be emitted as one beam again through said one lens. In a special case it may be desirable, however, to provide a different light beam. For example, a light beam that consists of a multitude of parallel light beams. If according to the second embodiment the lens comprises a multitude of lenses, all individual lenses can emit parallel light beams. Consequently it appears to next vehicles on the roadway, for which the light from the device is provided, as if the device comprises several light sources, which may contribute to the attention- drawing effect of the device. In a more specific embodiment, the lenses to that end lie in one plane, and in yet another embodiment the lenses are arranged in a matrix in said plane.

The lenses may be individually operative lenses, which are arranged in a lens assembly at the front side of the light incident in the housing; the lenses may also be lens elements/facets, however, which are arranged to form one lens.

If the lenses are arranged in a matrix in the plane, they may alternately be operative and non-operative in a special embodiment, or be arranged some distance apart in the plane, for example by alternately including a lens element and no lens element in each of the rows of the matrix, so that half the lens area comprises lens elements and the other half does not comprise lens elements. Said lens elements may or may not furthermore be arranged at varying positions in the rows, so that a lens matrix corresponding to the fields of a chessboard is obtained.

The present invention will be explained in more detail below with reference to the following figures, in which:

Figure 1 is a schematic view of the device according to an aspect of the present invention; and Figure 2 is a schematic view of the device according to an aspect of the invention.

Figure 1 schematically shows a longitudinal sectional view of a signal device according to a first aspect of the invention for placement along a roadway of a public road. Figure 1 in particular shows a roadside post used a roadsign for public road users. Figure 1 shows a housing 10 comprising an upper side wall 3 and a lower side wall 4. The side walls 3, 4 have a reflective surface for reflecting light incident on the side wall to the luminescent material on the photoluminescent surface 6. Said surface 6 is curved, viewed in a transverse cross- section of the housing 10, as is shown more clearly in figure 2, wherein, viewed in the direction of the right-hand side wall 1 1 of the housing 10, the surface 6 extends further toward the front side of the housing 10, where the lens 7 is disposed, than toward the left-hand side wall 9.

The inside of the housing 10 comprises a photoluminescent surface 6 near the rear wall 2. On said surface, a luminescent material is present. Said material is in particular a phosphorescent material, which emits an afterglow upon being irradiated with light from a headlight of a vehicle. Various kinds of phosphorescent material can be used for this purpose, depending on the required characteristics of the device. In the housing 10, a convex lens 7 is present at the front side thereof. Said lens converges incident light in the direction of the rear wall 2, onto the photoluminescent surface 6. In other embodiments, however, said lens may also be a concave, concave-plane, plane-concave, convex-concave or concave- convex lens.

Figure 1 shows the situation in which a beam of light 8, for example from headlights of a car on the roadway, is radiated in the direction indicated by arrows Pi. The beam of light 8 is incident on the lens 7 and is converged onto the photoluminescence surface 6 by said lens. Viewed in the vertical plane, the photoluminescent surface 6 is therefore spaced from the lens by a distance that corresponds to the focal distance. The electrons in the phosphorescent material are excited by the photons of the converged light beam 8. However, the electrons can also be excited by indirect light which is incident on the surface 6 from another direction Pt, via the reflective side walls 3, 4.

After being irradiated, the phosphorescent material will emit an afterglow. Subsequent vehicles on the roadway can benefit from this. Thus, an active signalling device or roadsign that does not need be supplied with power is provided. Under the influence of the afterglow effect of the phosphorescent material, light is radiated from the device again, via the lens 7, after the vehicle has passed, i.e. in the absence of the incident light.

Figure 2 schematically shows a cross-sectional view of the signalling device according to a first aspect of the invention. In figure 2, the housing 10 is shown again, in this case, however, with the left-hand side wall 9 and the right- hand side wall 1 1. This figure clearly shows that the photoluminescent surface 6 with the phosphorescent material lies in a curved plane. In this embodiment, the surface is curved so that the concave side of the surface faces the lens 7. In another embodiment, the surface 6 may also be configured as a cylinder, however, and consequently be convex over the entire area. In such an embodiment, the surface 6 forms part of a larger cylinder which comprises one or more lens elements 7 over the entire area thereof. The light can thus be radiated into the device from all sides and fall on the photoluminescent surface 6 via the lens.

In figure 2, position 16 indicates a light source (L), for example a headlight of a car. When said car is far removed from the device, the image point (B) 14 of said light source will be located substantially in the focus (F) of the lens and accordingly at the focal distance f from the lens 7. When the car on the roadway is moving in the direction of the device, however, the light source L will move as well. Due to the location of the device beside the roadway, the light source will become further and further removed from position 16. In a certain position of the vehicle on the roadway, the light source L will be located at position 17, for example. Consequently, incident light will converge in image point (B) 15 in the device via the beam 8. If the photoluminescent surface would be a straight surface, the material would no longer be located at the focal distance for such a position of the light source/car. Thus, the effect of the photoluminescent material is not optimal for those positions.

In the embodiment according to the invention as shown in figure 2, however, the photoluminescent surface is curved, the concave curvature of the surface being formed by the continuous line of image points from 14 to 15 formed by the movement of the light source from 16 to 17.

Figure 2 furthermore shows adjusting means 12 which can be used for adjusting the distance from the photoluminescent surface 6 to the rear wall 2. Using said adjusting means, the surface 6 can be positioned at a distance equal to, smaller than or larger than the focal distance relative to the lens. Said distance could in particular be adjusted in steps of 1 cm if the focal distance of the lens mounted in the housing 10 is 20 cm, for example. Relatively, the photoluminescent surface can be set in steps of 0.1 between 0.5 and 1.5 times the focal distance by means of the adjusting means 12.

In the appended figures and the above description, the present invention is shown and described merely by way of example on the basis of only one embodiment. It will be understood, however, that many variant embodiments, which may or may not be obvious to the skilled person, are conceivable within the scope of the present invention as defined in the appended claims. Where mention is made of a phosphorescent material in the figures, it is also possible to use another photoluminescent material, such as a fluorescent material. The use of the correct photoluminescent material depends on the desired afterglow period for a particular application and the cost of the material; the skilled person will be able to determine which material to use. The housing of the device is shown in a particular configuration and geometry herein. It will be understood that also in this regard variants that are obvious and known to the skilled person may be chosen.

In the description, the device is consistently described as a visual guide for vehicles on a roadway of a public road. However, the invention can also be used for other applications, preferably for applications in which the direction of incident light is known, but also for applications where this is not known in the variant of the cylindrical photoluminescent surface and the cylindrical lens disposed in front thereof. The application need not relate to guiding vehicles or persons moving forward, but the device may also be used as a recognition point in a more static situation.