EP0419229A2

EP0419229A2 - Improvements in or relating to signalling devices

Info

Publication number: EP0419229A2
Application number: EP90310241A
Authority: EP
Inventors: Ian Alexander Shanks
Original assignee: Thorn EMI PLC
Current assignee: Thorn EMI PLC
Priority date: 1989-09-20
Filing date: 1990-09-19
Publication date: 1991-03-27
Also published as: GB9009208D0; EP0419229A3; GB8921294D0; JPH03151406A

Abstract

A signalling device (1,2), such as a traffic cone, is constructed from a plastics material containing a fluorescent dye and bearing a marking (4). Light incident upon the device (1,2) causes flurorescence within the dye and fluorescent light so generated is constrained within the material such that the majority may only leave the device (1,2) via the marking (4).

Description

This invention relates to signalling devices, and it relates especially, though not exclusively, to such devices as may be used to convey information to the drivers of road vehicles.
There are many circumstances, for example in the vicinity of road works, traffic accidents, floods etc. where it is necessary for the drivers of vehicles to be advised of a danger or directed towards or away from a particular route or in general to be communicated with visually. At present, cones of plastics material are typically used in such circumstances, but such cones as are currently used convey little information other than that which is indicated by their physical presence.
In more permanent situations, fixed devices such as bollards can be used, but these are no more effective as information carriers than cones, particularly in conditions of darkness or otherwise poor visibility, unless they are connected to a supply of electricity which permits illumination of symbols or other characters.
Both cones and bollards can be made reflective and it has been proposed to use fluorescent, scattering and retroreflective materials to make them more readily visible. The problem still remains, however, that the bollard, or cone as the case may be, conveys little or no information (other than that indicated by its physical presence) unless it is connected to an external source of power.
German Patent Application DE 2934140 discloses a light source with a high light output and a large range of variation of the spectral intensity distribution. This active device uses fluorescent materials as a means to collect light produced by conventional lamps and concentrate it at output points.
It is an object of this invention to provide an improved form of signalling device.
According to the invention there is provided a light responsive signalling device including at least a portion fabricated from a plastics material containing a fluorescent dye for generating light by fluorescence within the material in response to light from an external source incident thereon, the plastics material bearing a marking in the form of a symbol or sign conveying information which it is desired to communicate, the marking being arranged such that at least a portion of the light generated by fluorescence is scattered or otherwise diverted from the plastics material in substantial conformity with the symbol or sign.
It is envisaged that such signalling devices in the form of traffic cones, for example, could be valuable in the provision of a more visible indication for drivers of road vehicles. In complete contrast German Patent Application DE 2934140 is essentially concerned with producing a concentrated beam of light from a point, although the finite point may be in the form of any geometrical shape.
In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described with reference to the accompanying drawings of which:

Figure 1 shows, in cross-sectional view, a device in accordance with one example of the invention and;
Figure 2 shows, in perspective view, part of the device of Figure 1.
Figure 3 shows, a device in accordance with a second example of the invention. Figure 4 shows, in plan view, the device in Figure 3.

Referring now to the drawings, the device shown therein comprises a traffic cone of which at least the upper part 1 is constructed of a plastics material such as polycarbonate, containing an organic fluorescent phosphor dye. If desired, combinations of layers containing different fluorescent dyes can be used to produce various colours (including white). A suitable plastics material is that known as Lisa, developed by Bayer in West Germany. The base part 2 of the cone may or may not be formed of or include fluorescent material and it may be weighted for stability if desired. Conveniently, the region 3 of the cone is formed with or otherwise supports material capable of reflecting or diffusing incident light on the upper part 1.
The material of the upper part 1 of the cone is shaped and configured to ensure that most of the light generated by fluorescence therein is constrained to remain within the material until it encounters a scattering or other diverting agency. In this example it will be observed that the thickness of the plastics material increases as the cone tapers.
In accordance with this example of the invention, the scattering or diverting agency comprises a carved or sculpted symbol 4 (see Figure 2) in the internal or external surface of the upper part 1 of the cone. Alternatively, or in addition, the agency could comprise a layer of paint or other suitable substance printed or otherwise applied to or deposited on the inner surface of the upper portion 1 of the cone in accordance with the desired form of symbol 4.
In either event, a substantial amount of the light generated by fluorescence within the upper portion 1 emerges therefrom in substantial accordance with the shape of the symbol which, in this instance, consists of a "keep left" arrow.
It will be appreciated that this arrangement is straightforward and practically more useful than the assembly of symbols such as arrows from matrices of point light sources such as, for example, provided by German Patent Application DE 2934140.
It is feasible that marks such as fingerprints, for example, on the plastics material might act as scattering-out points, thus reducing the intensity of light available at desired light emergency positions. Hence the fluorescent plastics material may if desired be "shrink-wrapped' in a comformable plastic as there would then always be an air film between the shrink wrapper and the cones and thus marks such as fingerprints on the plastic wrapper would not undesirably interfere with light emission.
Additionally or alternatively, convenient techniques such as metallising, or the use of a non-contacting light scatterer, can be used to couple back into the cone light which might otherwise be lost, e.g. at the edges of the cone.
It will be appreciated that, under conditions of daylight and/or illumination by vehicle head-lamps and/or artificial light, the material of the upper portion 1 will respond to the incidence of such light by fluorescing and since the collection area and fluorescing volume of the cone is very much larger than the region of light emission (i.e. the vicinity of the symbols) there is a significant concentration of light which causes the symbol region to glow brightly relative to its immediate surroundings.
Thus, with no requirement for a local power source, the invention provides for the communication of visual signals of enhanced brightness compared with their background. It will be appreciated that a local power source may be added if required.
It will be appreciated that a device in accordance with this example of the invention is capable of showing the symbol 4 in one direction in response for example to illumination from the headlamps of vehicles travelling in the opposition direction, or approaching at some other angle.
It will also be appreciated that the invention is not limited in its application to the field of traffic cones but may be used in any situation where it is desired to convey information by visual signalling and where the device carrying the symbol or other form of visual information is or can be illuminated.
In an alternative arrangement, the upper part of the cone may be made of clear plastics material 5 and fluorescent plastic elements, for example of triangular form 6, may be solvent welded 7 edge-on to the inner surface of the cone in a predetermined format (see Figures 3 and 4). The fluorescent plastic elements are preferably left free at their innermost surfaces so that the cones can be stacked on top of one another for storage.
Alternatively, the cones may be made collapsible by forming a number of sections that are retained together by suitable latching arrangements when extended. This would provide for improved storage efficiency.
In yet another arrangement a fluorescent cylinder may be used inside a protective, clear cone.
Alternatively, the light responsible signalling device may take the form of a shroud or cover for use with conventional traffic cones.
It will be appreciated from the foregoing that a large area of the surface of the fluorescent plastic has to be exposed to the ambient light (or at least to the appropriate wavelengths in ambient light) in order to drive the fluorescence and light concentrating processes. This means that this surface cannot be covered significantly with a conventional retroreflecting layer since such layers are opaque and would prevent ambient light entering the fluorescent plastic over this area. Putting a retroreflecting layer underneath the fluorescent plastic layers causes the retroreflected light to be reduced in intensity and coloured by the absorption of the fluorescent plastic, i.e. it cannot be white. It can be most advantageous to permit light concentration from an area covered by a retroreflecting layer so that the headlights of a car are retroreflected brightly while other ambient light sources are concentrated to give light emission, and the following embodiment of the invention achieves this.
In this embodiment, a plastic foil, embossed with corner-cubes on its rear surface, retroreflects light entering its front surface within a range of angles (e.g. 30 degrees) either side of the normal to the foil. This involves (total internal) reflections from the faces of the corner-cubes on the rear surface. Outside this range of angles, these reflections become insignificant and incident light is transmitted through the foil and emerges from the rear surface. Such a foil may be obtained by removing the back (translucent) layer from a transflective corner-cube retroreflector such as that made by Reflexite Limited (Transflector, non-adhesive, Nos. D50-15000180 or D52-1800-180).
If this is placed over the central portion of a fluorescent plastic layer, e.g. on a cone, it retroreflects light near normal incidence but allows obliquely incident light to pass through to stimulate the fluorescence and light concentrating processes in the fluorescent plastic. Thus light may be emitted from the regions above or below the retroreflector, or even from behind the retroreflector provided that it is viewed obliquely. Due to the curvature of a conical shape the white light from the headlights of a car is retroreflected back to the driver from this central portion over most of its width, whilst light falling near the edges of the cone is transmitted to pump the fluorescent plastic and cause light to be emitted from the desired areas or symbols. The retroreflected light may be coloured if desired by using a suitable filter layer which does not significantly absorb the wavelengths required to stimulate the fluorescence.
The effect of the foregoing embodiment is that the light emitting areas of a cone or display sign (e.g. the border of a number plate) will glow brightly in daylight, road lighting (not low pressure sodium unless the fluorescent plastic is red), moonlight and in the light from other vehicles which are oncoming, in front or behind. Light from a car's own headlights is, however, very brightly retroreflected from the central area of the cone or display sign as in a conventional cone or number plate.
In a preferred embodiment, a final layer of transparent material is sealed or otherwise provided over the fluorescent plastic and retroreflector to prevent dirt and moisture from degrading these too much in use.
Alternatively, the retroreflector may be made by embossing corner-cubes over part of the inside surface of this protective layer, or the transparent sheet may be welded to the edges of the retroreflector.
In the event that any of the foregoing embodiments or examples of the invention is used as a cone or bollard, there may be advantage in constructing the object in question in the form of a three- or four-sided pyramid rather than a true cone with circular geometry.

Claims

1. A light responsive signalling device including at least a portion fabricated from a plastics material containing a fluorescent dye for generating light by fluorescence within the material in response to light from an external source incident thereon, then plastics material bearing a marking in the form of a symbol or sign conveying information which it is desired to communicate, the marking being arranged such that at least a portion of the light generated by fluorescence is scattered or otherwise diverted from the plastics material in substantial conformity with the symbol or sign.

2. A device according to claim 1 constructed to constitute a free-standing traffic cone or bollard.

3. A device according to claim 1 or claim 2 wherein the plastics material is disposed and configured such that a majority of the light generated by fluorescence of the dye is constrained within the plastics material except at the marking.

4. A device according to any one of the preceding claims wherein the symbol or sign is carved or sculpted into or upstanding from a surface region of the plastics material.

5. A device according to any one of claims 1 to 3 wherein the symbol or sign is printed or otherwise deposited on a surface region of the plastics material.

6. A device according to any one of the preceding claims further including retroreflective material located over at least part of the plastics material and arranged to retroreflect light incident thereon over a predetermined range of angles only and to allow light incident thereon at angles outside the predetermined range to reach the plastics material so as to stimulate the fluorescence of the dye therein.

7. A device according to any preceding claim further including a layer of optically transparent material, which transparent material substantially overlies the plastics material.