DIFFUSOR

Abstract: A diffusor for use with a traffic sign or the like which displays an illuminated symbol has a central opaque zone (10) adapted to reduce light transmission through the portion of the symbol on and adjacent to the optical axis of the sign, a second opaque zone (11) on the inner face of the diffusor adapted to transmit more light than the central portion and a third opaque zone (12) on the outer face of the diffusor adapted to transmit more light than the central zone. The second and third zones are not necessarily being in alignment and the third zone may transmit more light than the second zone.

Description: DIFFUSOR TECHNICAL FIELD This invention relates to illuminated traffic signs such as pedestrian WALK and DON'T WALK signs. BACKGROUND ART Illuminated pedestrian signs normally consist of a housing, a light source in the housing, a lens for distributing transmitted light, a masking means between the lens and the light source to restrict the transmitted light to a predetermined pattern and a diffusor between the light source and masking means to modify the illumination of the predetermined pattern. Some pedestrian signs of the kind having a symbol of a man have employed a clear plastics diffusor which is a segment of a sphere and is dimensioned to overlie the pattern or symbol of the man on the masking means. In order to modify the illumination of the symbol, the diffusor has a central opaque portion which may be formed by spark-eroding both surfaces of the die in which the diffusor is formed in the vicinity of the centre so that the diffusor has an embossed opaque surface on both its convex and concave faces at and around its optical axis. Although such modification of the diffusor does enhance that illumination of the symbol, signs fitted with these diffusors do not achieve the high optical performance specified by Australian Standards and various local government user specifications. The critical area of the illumination requirement is that there is to be an even illumination of the symbol on display and it is an object of this invention to provide an improved diffusor for an illuminated traffic sign which provides a more even illumination of the symbol on display that has been achieved with prior art traffic signs. SUMMARY OF THE INVENTION According to the invention there is provided a diffusor for use with a traffic sign adapted to display an illuminated symbol, said diffusor comprising a central opaque zone adapted to reduce light transmission through the portion of the symbol on and adajcent to the optical axis of the sign, a second opaque zone on the inner face of the diffusor adapted to transmit more light than the central portion and a third opaque zone on the outer face of the diffusor adapted to transmit more light than the central zone, the second and third zones not necessarily being in alignment. The invention also provides a method of manufacturing a diffusor for use with a traffic sign adapted to display an illuminated symbol in which a die from which the diffusor is formed is spark-eroded at predetermined portions to provide a central opaque zone on and adjacent to the optical axis of the sign, a second zone on the inner face of the diffusor and a third zone on the outer face ofthe diffusor, said second and third zones being adapted to transmit more light than the central zone and not necessarily being in alignment. BRIEF DESCRIPTION OF THE DRAWINGS;- In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings in which: Fig. 1 is a plan view of a diffusor according to one embodiment of the invention, and. Fig. 2 is a view taken along lines A-A of Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENT An illuminated traffic sign normally includes a box¬ like housing having an open front face in which is mounted a parabolic reflector. A lamp holder supported by the reflector carries a lamp, the filament or light source of which is located at the focus of the reflector. Light from the light source is directed by the reflector into a generally horizontal beam on the optical axis of the sign. The lens or reflector overlies the reflector and the light source and is sealed at its circumference to a cover plate which closes the housing. The refractor is molded from a polycarbonate material to provide a body portion that is a segment of a sphere and a mounting or sealing rim by means of which the lens is sealed in the cover plate. On the inner concave surface of the body portion of the refractor there is formed a ray of lenticular elements which are arranged in rows that extend generally horizontally across the lens. The cover plate also supports a masking plate which is also a segment of a sphere so that it may be mounted against the inner or concave face of the refractor. A diffusor is mounted on the inside of the masking plate and to this end is similar in curvature to the masking plate and is dimensioned to overlie the symbol formed on the masking plate. A diffusor according to one embodiment of the invention isshown in Figs. 1 and 2. The diffusor is injection moulded in clear polycarbonate. The central portion 10 of the diffusor is modified to provide an opaque zone adapted to reduce light transmission through the portion of the symbol on or adjacent to the optical axis of the sign. The central opaque zone 10 is, in this instance, formed by spark-eroding the appropriate portion of the die in which the diffusor is made. In accordance with the invention, the diffusor is further modified by providing a second opaque zone 11 on the inner face of the diffusor that surrounds the central opaque zone and which is adapted to transmit more light than is transmitted through the central zone. The second opaque zone 11 is also formed by spark-eroding the appropriate portion of the die in which the diffusor is made. In order to achieve the desired result of more light transmission through the second opaque zone, the spark-erosion of the die which creates the second opaque zone is less than that done to create the central opaque zone. A third opaque zone 12 is formed on the outer or convex face of the diffusor and is adapted to transmit more light than the central zone. The third opaque zone is formed in the same way as the second opaque zone and its light transmission capabilities may be more or less than that of the second opaque zone but always will transmit more light than the central opaque zone. The shape and configuration of the second and third opaque zones will depend, in the main, upon the configuration of the symbol on the masking plate. The light transmission characteristics of the second and third opaque zone need not be constant over the entire zones but may vary as required to ensure that the sign provides the required illumination. Although the invention has been described in relation to the provisions of the second and third opaque zones by spark-eroding the die from which the diffusor is made, the first, second and third opaque zones may well be formed by sandblasting or otherwise treating the diffusor. In a preferred form of the invention, the die is spark eroded to provide an opaque finish on the surface of the diffusor so that: (a) the central zone is adapted to reduce the light transmission of the diffusor by 60%, (b) the second zone is adapted to reduce the light transmission of the diffusor by 40%,and (c) the third zone is adapted to reduce the light transmission of the diffusor by 20%. Various modifications may be made in details of design and manufacturing techniques without departing from the scope and ambit of the invention.

Claims: CLAIMS 1. A diffusor for use with a traffic sign or the like adapted to display an illuminated symbol, said diffusor comprising a central opaque zone adapted to reduce light transmission through the portion of the symbol on and adjacent to the optical axis of the sign, a second opaque zone on the inner face of the diffusor adapted to transmit more light than the central portion and a third opaque zone on the outer face of the diffusor adapted to transmit more light than the central zone, the second and third zones not necessarily being in alignment. 2. A diffusor according to claim 1 wherein the diffusor is formed by moulding a plastics material and the central, second and third zones are formed by deformations on the mould. 3. A diffusor according to either of the preceding claims wherein the third zone is adapted to transmit more light than the second zone. 4. A duffusor according to any one of the preceding claims wherein:- (a) the central zone is adapted to reduce the light transmission of the diffusor by 60%, (b) the second zone is adapted to reduce the light transmission of the diffusor by 40%, and (c) the third zone is adapted to reduce the light transmission of the diffusor by 20%. 5. A diffusor according to any one of the preceding claims wherein the light transmissibility of each said zone is not constant over each said zone. 6. A method of manufacturing a diffusor for use with a traffic sign or the like adapted to display an illuminated symbol in which a die from which the diffusor is formed is treated at predetermined portions to provide a central opaque zone on and adjacent to the optical axis of the sign, a second zone on the inner face of the diffusor and a third zone on the outer face of the diffusor, said second and third zones being adapted to transmit more light than the central zone and not necessarily being in alignment. 7. A. method according to claim 5 wherein the die is spark eroded. 8. A method according to claim 5 or claim 6 wherein:- (a) the central zone is adapted to reduce the light transmission of the diffusor by 60%, (b) the second zone is adapted to reduce the light transmission of the diffusor by 40%, and, (c) the third zone is adapted to reduce the light transmission of the diffusor by 20%. 9. A method according to any one of claims 6 to 8 wherein the light transmissibility of each said zone is not constant over each said zone.

Inventors: HOLST BARRIE JAMES, HOLST, BARRIE, JAMES
Applicants: ALDRIDGE TRAFFIC SYSTEMS, ALDRIDGE TRAFFIC SYSTEMS PTY. LTD.
Application year: 1986
Main classification: G02B5
IPC codes: G02B5, G08G1