Retro-reflective road studs are well known in the art. These studs are normally mounted in spaced relation relative to one another along a centre and/or side line of a road. Light emitted by the head lights of a first vehicle traveling in a first direction is reflected in an opposite or reverse direction by the stud, to make the stud and hence the line on which it is mounted better visible to a driver of the first vehicle. A problem with this system is that when a second vehicle is approaching the first vehicle from an opposite direction, the head lights of the vehicles ought to be dipped.

The result is that only a few nearby studs reflect light back to the drivers of the vehicles and accordingly the visibility of the line is reduced. Furthermore, the head lights of the approaching vehicle tend to at least partially blind the driver of the other vehicle. Hence, for at least a critical period while these two vehicles are approaching one another from opposite directions, the known road studs and accordingly also the lines on which they are mounted are often not sufficiently visible to either of the drivers. OBJECT OF THE INVENTION Accordingly, it is an object of the present invention to provide an alternative road sign, more particularly a road marker and associated method with which the applicant believes the aforementioned disadvantages may at least be alleviated.

SUMMARY OF THE INVENTION According to the invention, there is provided a road sign comprising: a body; - a photodetector on the body; the photodetector being configured on the body to be sensitive to illumination by headlights of a first vehicle approaching the body in a first direction; the photodetector being connected in a circuit on the body also comprising a light emitting device; the circuit being configured to energize the light emitting device in response to illumination of the photodetector by the head lights of the first vehicle; and the light emitting device being mounted on the body to enhance visibility of the body.

The light emitting device preferably emits light in a direction wherein visibility of the body is enhanced for a driver of a second vehicle being driven in a direction other than the first direction.

In one embodiment of the invention the body may be the body of a vehicle carrying the sign.

In another embodiment, the sign may be in the form of a road side marker.

In yet another embodiment, the sign may be in the form of a road surface mountable stud and wherein the body is configured to be mounted on a road surface.

In some embodiments, the photodetector may be a photoswitch connecting the light emitting device to a power supply.

The power supply may be externally of the body and in other embodiments at least part of the power supply may be mounted on the body of the sign.

The power supply may comprise a photosensitive power source and a charge storage device.

In other embodiments, the photodetector is connected to the light emitting device to act as power supply and to power the light emitting device upon illumination of the photodetector. A photoswitch may be connected in the circuit with the photodetector and the light emitting device.

The photodetector may be mounted on one sidewall of the body and the light emitting device may be mounted on another sidewall of the body, such as an opposite sidewall.

A retro-reflector may be mounted on at least one of said one sidewall and said other sidewall of the body.

Also included within the scope of the present invention is a method of signaling to traffic on a road, the method comprising the steps of: providing a road sign comprising a body carrying a photodetector and an electrical circuit connecting the photodetector to a light emitting device on the body; utilizing impinging light emitted by headlights of a first vehicle traveling in a first direction to cause the photodetector to cause energization of the light emitting device; and - causing the light emitting device to emit light to enhance visibility of the body.

The method may comprise the further steps of causing a light reflector on the body to reflect the impinging light in an opposite direction towards the first vehicle and causing the light emitting device to emit light in a direction wherein visibility of the body is enhanced for a driver of another vehicle which is being driven in a direction other then the first direction.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein figure 1 is a diagrammatic representation of a road section, two mutually approaching vehicles on the road section and a plurality of known road studs mounted on a centre line of the road section; figure 2 is a diagrammatic perspective view of one embodiment of a road marker according to the invention, in the form of a road surface mountable road stud according to the invention; figure 3 is a very basic block diagram of part of an electric circuit forming part of said one embodiment of the road stud according to the invention; figure 4 is a similar diagram showing other detail of the stud in figure 2 according to the invention; figure 5 is a basic block diagram of a second embodiment of the stud according to the invention; figure 6 is a block diagram of an external power supply connected to a plurality of road studs according to the invention; figure 7 is a diagrammatic representation of another road stud; and figure 8 is a diagrammatic representation of a further road sign according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION In figure 1 , there is shown a conventional road 1 0 having a center line 1 2.

On the line there are mounted in known manner a plurality of road studs 1 4. 1 to 14.n. A first vehicle 1 6 travels in a first direction A and a second vehicle 1 8 travels in an opposite direction B.

The known road stud comprises a body mountable on the road surface and carrying a retro-reflector. The reflector in use reflects back in direction BJmpinging light 1 7 emitted by the head lights of the vehicle 1 6. This reflection makes the stud and hence the line more visible to a driver of vehicle 1 6. However, when a second vehicle 1 8 approaches the first vehicle, the lights of the vehicles ought to be dipped. This causes the problem referred to in the introduction of this specification in that only one or two nearby studs are illuminated by the head lights of the vehicles to reflect light to the driver of the relevant vehicle, and which problem is aggravated by the temporary blinding effect of the light emitted by the headlights of the other vehicle.

A road sign in the form of a road surface mountable road stud 20 according to the invention is shown in figures 2 and 3. The stud 20 comprises a body 22, which may have a conventional shape and configuration. The body comprises a base that is mountable on a road surface, to abut against the road surface. The body further comprises known low profile sidewalls 28 and 31 rising in slanting fashion from the base. On at least one of the sidewalls 28, the body 22 carries a conventional retro-reflector 24 for reflecting impinging light propagating in direction A in an opposite direction B. The body further carries a photodetector 26 in the form of a photoswitch on the sidewall 28 thereof and facing in direction B.

The photoswitch 26 is electrically connected in a circuit 32 (shown in figure 3) to a light emitting device 30 and charge storage device 34. The light emitting device 30 may be a light emitting diode (LED), is mounted on opposite sidewall 31 of the stud and emits light in direction A, that is in a direction opposite to the direction B wherein the reflector 24 reflects the impinging light. When light emitted by the head lights of vehicle 16 traveling in one direction, such as direction A impinges on the photoswitch 26, the circuit 32 is closed, so that the LED is energized. The LED emits light in direction A, so that the body 22 of stud 20 is better visible to the driver of an approaching second vehicle 1 8, being driven in another direction, such as opposite direction B.

Further features of the circuit are shown in figure 4. The charge storage device 34 may be in the form of a capacitor or rechargeable battery 34 and is connected via a suitable charger circuit 36 to be charged by power generated by an on-board supply 37 and/or from another external supply. As stated hereinbefore, in this embodiment, the photoswitch 26 is configured to close the circuit 32 upon illumination thereof by light emitted by the headlights of approaching traffic.

In another form of this embodiment of the stud, a second and similar photoswitch may be provided on sidewall 31 to cause energization of a second LED provided on sidewall 28. In yet another form, a single photoswitch may be provided in a suitable position on the body 22 to cause energization of both the LED's simultaneously. A second retro- reflector may also be provided on sidewall 31 .

Another embodiment of the stud is shown at 40 in figure 5. The stud body 42 carries a photodetector arrangement 26 which is connected via optional day/night switch 38 to the light emitting device 30. During the day, the switch is normally open. In this embodiment, the LED 30 is energized by current generated at the arrangement 26, as a result of illumination of arrangement 26 by the head lights of an approaching vehicle. Hence, in this embodiment the arrangement 26 acts as power supply or voltage source or current source and not as a mere switch as in the previous embodiment. A charge storage device 34 may be provided over the arrangement 26 as shown in figure 5. A conventional retro- reflector is shown at 24.

In figure 6 a plurality of studs 50.1 to 50. n are provided on a road surface 52 on a line 54. Each stud comprises a respective body 56 carrying a respective light emitting device 58.1 to 58. n. The devices may emit light in predominantly a selected direction as hereinbefore described, or omni-directionally. Electrical power for energizing the devices is derived from an external power source 60. The external power source may be mounted on the road side and may comprise a solar panel 62 or any other suitable means for generating electricity. The source may comprise a local storage device such as a rechargeable battery 64. The source is connected by a circuit 68 to the devices 58.1 to 58. n, to power and drive same. Photoswitches similar to switch 26 in figures 2 and 3 may be provided on the stud bodies in series with the respective LED's 58.1 to 58. n, to ensure that the LED is energized only when the photoswitch is illuminated by the head lights of approaching traffic.

In figure 7 there is shown an alternative stud designated 70. The stud 70 comprises a body 72 and the body is configured to receive at face 74 thereof light impinging in direction A and to transmit and/or reflect the light through the body and beyond face 76 thereof in direction A. The body may be transparent or translucent. Alternatively, the body may comprise a mirror arrangement for receiving and reflecting the impinging light in direction A. The body may further comprise fluorescent and/or phosphorescent means.

A sign 80 according to the invention may be provided on a carrier vehicle as shown at 80 in figure 8. In the diagram the sign is shown where it is mounted on a rear end of the carrier vehicle 82. However, at least part of the sign, for example the light emitting devices thereof, may be mounted on other parts of the carrier vehicle, such as on the sides 85 thereof. The sign 80 comprises at least one photodetector 84 connected by an electrical circuit (not shown) to at least one light emitting devices 86. When illuminated by the head lights of a following vehicle for example, the detector 84 causes the light emitting devices to be energized, to emit visible signals towards a driver of the following vehicle and/or even a third vehicle. Especially when the light emitting devices are mounted on the sides of the carrier vehicle, they may, when energized, make the carrier vehicle better visible to the driver of another vehicle, including the driver of a third vehicle being driven in another direction.

In other applications, a similar arrangement may be used on road side markers or furniture to demarcate a hazardous area or section on a road.

The light emitting devices in all of the aforementioned embodiments may emit light in the red or orange or green parts of the visible spectrum. In other embodiments broad spectrum white light may be emitted.

The aforementioned electrical circuits may comprise means for pulsing energization of the light emitting devices intermittently, including periodically.