LIGHT TRANSMITTING PLATE MEMBER

Abstract: By a light transmitting plate member (2) for illuminated signs, illuminated tables or similar illuminated flat items and intended for uniform diffusion of light from a light source positioned at a side edge (6) of the light transmitter (2) which has a flat side (8) and an opposing side which has a gradual slope, the plate member having a reduced thickness in the direction away from said end edge (6), said opposite sides are produced with optically smooth surfaces as the light transmitting plate member (2) consists of transparent and light transparent material with specific optical properties, the said side with the gradual slope is provided with a number of angled divisions (4) which are defined by transverse divisional lines which run parallel to the side edge (6) and which are positioned with either uniform intervals or with graded intervals which are reduced in the direction receding from said side edge (6), in that the thickness of the light transmitting plate member at the transverse divisional lines corresponds to the thickness of the light transmitting plate member (2) at the side edge (6), whose angled divisions (4) from said divisional lines and in the direction away from the side edge (6) have reducing thicknesses.

Description: LIGHT TRANSMITTING PLATE MEMBER The present invention relates to a light transmitting plate member for illuminated signs, illuminated tables or similar illuminated flat items and of the type described in the introductory part of claim 1. A such light transmitter or light source by way of example is known from the description to Danish Patent Application No. 3800/84. Furthermore, this known light source in general is described in the earlier published description to US Patent No. 3,464,133 dealing with a display apparatus comprising a number of successively activated light sources as the apparatus is adapted to animate a multi-dimensional picture when this is observed from the front side of a prismatic light transmitter being illuminated from a narrow side edge by means of one or more light sources. These known devices and moreover also the light transmitting plate member according to the invention are based on the particular optical and/or light technical conditions which a ray of light being introduced from a side edge of a prismatic member is reflected from opposite surfaces of the member with a still reduced angle of refraction as this for each reflection is reduced with the cone angle of the prism, i.e. the angle of inclination between the opposite surfaces of the prism. By introducing not only a single ray of light but a pencil of rays of light under different angles of incidence into the light transmitter is obtained a rather uniform diffusion of the reflected and finally transmitted rays of light from the light transmitter. As a matter of fact there is also applied a lower as an upper critical angle of refraction determined by the index of refraction for the actual material from which the light transmitting plate member is produced. The invention has for its purpose to provide an improved light transmitting plate member of the introductory described type and by means of which by simple measures may be obtained a considerably better and uniform diffusion of light - also by light transmitting plate members having a considerable length. According to the invention the light transmitting plate member is characterized by said side with the gradual slope being provided with a number of angled divisions which are defined by transverse divisional lines which in general run parallel to said first side edge and which are positioned with either uniform intervals or with graded intervals which are reduced in the direction receeding from said first side edge, in that the height or the thickness of the light transmitting plate member at the transverse divisional lines in general corresponds to the thickness of the light transmitting plate member at said first side edge, whose angled divisions from said divisional lines and in the direction away from said first side edge have reducing thicknesses, i.e. are inclined in relation to a reference plane parallel to said first particular plane side of the light transmitting plate member. Hereby is obtained a quite new and improved type of light transmitting plate member which may be produced with a considerably less self-weight per unit of length and which is suitable for production by extruding, whereby also the costs of production may be minimized - of course on condition of a reasonably large production. Furthermore, the light transmitting plate member according to the invention shows a considerably increased efficiency as to uniform light diffusion ability - even with a rather considerable total length. By way of example the light transmitting plate member according to the invention may be produced from a rather cheap acryl plate, e.g. having an initial thickness of about 10 mm and with a length of up to about 1400 mm and a width which nearly alone is determined by the width of the item which is to be illuminated - and of course the actual used light source i.e. the length of, by way of example, a low voltage tub lamp (PL-lamp ) . Preferably, the angles of inclination of said angled divisions of said opposite side and the said mutual length between said divisional lines are varied in such a manne that each of said angled divisions or gradual slopes ar illuminated approximately uniform by light diffusion from th the respective sides of the light transmitting plate member of which the said first preferable plane side is considere as the front side of the light transmitting ' plate membe which is preferably turned against the item which is to b illuminated e.g. a sign plate, while said opposite side o the light transmitting plate member with said gradual slope is considered as the rear side of the light transmittin plate member whereby preferably a reflector is positione being adapted to reflect the light right through the ligh transmitting plate member, i.e. out through the plane fron side thereof. Appropriately, the light transmitting plate " member is . ' produced from a preferably plane acryl plate of minor thickness, e.g., 5 - 15 mm, preferably 10 mm and with a considerable length, e.g. 200 - 1400 mm, preferably about 1200 mm, as said angled divisions are varying from about 0.1° - 5° nearest at said first side edge to about 5° - 20° farthest of from said first side edge - dependent on the total length of the light transmitting plate member. In the following the invention is described in more details reference being made to the accompanying drawing, in which:- Fig. 1 is a side view - partly in section - of an embodiment of a light transmitting plate member according to the invention, shown almost in natural size in five parts, Fig. 2 is a side view - partly in section - of another embodiment of a light transmitting plate member according to the invention. Fig. 3 is a perspective view of an illuminated sign provided with a light transmitting plate member according to the invention, while Fig. 4 is a perspective view of the illuminated sign shown in Fig. 3 - seen from the opposite side. The light transmitting plate member shown in Fig. 1 is - as alluded - produced from a limpid acryl plate with an initial thickness of about 10 mm and with a plate geometry which is shown in the below table 1, in which -the lengths of the left column are representing the longitudinal extent of angled divisions 4 of the light transmitting plate member which as a unit is designated 2 as the length of the angled divisions 4 are each 20 mm and all being measured "from a left side edge 6 of the light transmitting plate member, i.e. that the measures shown along a plane front side 8 thereof are also to be found in the left column of table 1. To save space the light transmitting plate member 2 of Fig. 1 is divided into 5 uniform pieces of each 240 mm. Also to save space table 1 is shortened by omission of some partial sections of the plate geometry of the light transmitting plate member 2. The middle column of table 1 shows the height or the thickness of the light transmitting plate member 2 at the respective crossings between said angled divisions 4, while the right column of table 1 shows the respective inclination angles of the divisions in relation to a reference plane parallel to the plane front side 8 , as the vertical interval ' s between the divisions 4. are indicated as 90° angles. The plate geometry shown is calculated by computer as the length of each divisions 4 and the plate thickness at the crossings between the divisions have been kept as predetermined constants on 20 and 10 mm, respectively. Besides, the method of calculation has aspired to uniform light diffusion in the light transmitting plate member 2 which by way of calculation has been supplied with pencils of light rays which have been introduced from the center of the left side edge 6 by angles of incidence from -42° to +42° TABLE 1 (Plate geometry - Fig. 1) Length (mm) Height (mm) Angle (°) 0.000 10.000 -0.600 20.000 9.791 90.000 20.000 10.000 -0.600 40.000 9.791 90.000 40.000 10.000 -0.600 60.000 9.791 90.000 200.000 10.000 -0.600. 220.000 9.790 90.000 220.000 10.000 -0.600 240.000 9.790 90.000 320.000 9.790 90.000 320.000 10.000 -0.602 340.000 9.790 90.000 340.000 10.000 -0.603 360.000 9.790 90.000 360.000 10.000 -0.604 380.000 9.789 90.000 560.000 9.774 90.000 560.000 10.000 -0.659 580.000 9.770 90.000 580.000 10.000 -0.674 740.000 10.000 -0.967 760.000 9.662 90.000 760.000 10.000 -1.039 780.000 9.637 90.000 780.000 10.000 -1,123 980.000 10.000 -3.125 1000.000 8.908 90.000 1000.000 10.000 -3.509 1180.000 1,0.000 ■ 10.000 1200.000 6.473 90.000 1200.000 0.000 0.000 as consideration has been taken to the lowermost angle of limitation a little under 42° of the material in question - acryl. Concerning the used optical/light technical rules of calculation see the descriptions to Danish Patent Application No. 3800/84 and US Patent No. 3,464,133 which rules of calculation hereby are included in the present description. Furthermore is refered to the description to US Patent No. 4,059,916. Another embodiment of a light transmitting plate member 12 according to the invention is shown in Fig. 2. This light transmitting plate member 12 is also produced from limpid TABLE 2: (Plate geometry - Fig. 2). Length (mm) j Height (mm) I Angle (°) acryl with a plane front side 14 and a rear side 16 which i provided with angled divisions 16, i.e. with a plate geometry, which in full is indicated in the accompanyin table 2, in which the middle column like table 1 indicate the actual height or thickness of the light transmittin plate member 12 at the respective crossings between th angled divisions 16, while the right column of table indicates the actual angles of inclination of the division 16 and the right-angled edge portions at the crossings between the angled divisions 16, respectively. In this case the plate geometry is also calculated by means of a computer - as assumption has been constant values of the heights or the plate thickness at the crossings between the divisions 16 and predetermined angle intervals of the angles of inclination of the angled divisions 16, viz. an initial angle on -0.5° adjacent to the left side edge 18 of the light transmitting plate member 12 to a final angle of -7.0° farthest away from the side edge 18. On the ' assumption that the light transmitting plate member 12 should give an approximate uniform light diffusion summed up along opposite side surfaces .thereof the respective lengths of the divisions 16 are then calculated as indicated in the left column of table 2 and in Fig. 2, respectively. Also in this case the light-technical assumptions have been that light is introduced into the light tranmitter 12 along a center line of the side edge 18 with angle limitations from -42° to +42°. The light transmitting plate member 12 is as the case of the light transmitting plate member 2 shown in Fig. 1 produced from a limpid acryl plate with an initial plate thickness of 10 mm and a total length of about 550 mm. The illuminated sign 22 shown in Figs. - 3 and 4 is provided with a light transmitting plate, member 24 of the same type as the light transmitting plate member 2 cfr . Fig. 1 and table l,i.e. with uniform longitudinal extension of the angled divisions 4 and with increasing angles of inclination seen in the direction receeding from the side edge 6, whereby a light source in the form of a tubular lamp 26 is placed in a lamp housing 28 into which is inserted the side edge 6 of the light transmitting plate member 2. The lamp housing 28 and the illuminated sign 22 as a whole is surrounded of a not shown light tight edge frame in which furthermore a rearmost reflector plate member 30, the light transmitter 2 and a front sign plate member 32 are mounted. Preferably the sign plate member 32 consists of an opalescent glass plate or a white transparent acryl plate on which the actual sign text or other sign decoration is directly printed. As shown - the tubular lamp 26 of the illuminated sign 22 is surrounded by a reflector shade 34 being tightly connected to the side edge 6 of the light transmitter 2. The tubular lamp 26 used may be a low voltage lamp, e.g. 9 , PL-lamp, which has shown to be satisfactory to illuminate a sign plate of 200 x 1200 mm in an approximately quite uniform manner. A further and alternative plate geometry of the light transmitting plate member appears from table 3 below, where the assumptions for the calculation have been the number, viz. 10 angled divisions and constant values of the heights or the plate thickness at the crossings between the respective angled divisions. These heights are cfr. the middle column constant, viz. 8 and 10 mm, respectively. On the other hand table 3 also shows -varying angles of inclination of the angled divisions as varying longitudinal extension of the angled divisions which as earlier all are measured from the side edge where the light source is adapted to be placed. The light-technical assumptions have been the same as' in tables 1 and 2. TABLE 3: (Plate geometry - alternative) Length (mm) I Height (mm) I Angle (°) In order to illustrate the efficiency of the light transmitting plate member according to the invention, reference is made to the accompanying table 4 which indicates TABLE 4: (Light diffusion - %) . Front side Rear side Total the light diffusion in % for an alternative light transmitting plate member with a total length of 1200 mm, a plate thickness of 10 mm, 40 numbers of sloped surfaces each with a length of 30 mm, an initial angle of -0.450° and a final angle of -10.000° (i.e. a light transmitting plate member of the same type as shown in Fig. 1 and table 1, respectively) . Table 4 indicates the light diffusion, i.e. the amount of light radiated from divisions of 120 mm (corresponding to 4 angled divisions of each 30 mm) of as well the plane front side as the "saw-tooth-scaped" rear side. In right column is indicated the total amount of light from the respective divisions as it is assumed that all light radiates through the plane front side to the sign plate, because a reflector plate member is placed at the rear side of the light transmitting plate member. Cfr. table 4 no light at all radiates- from the respective surfaces of the first division of the light transmitter, because this, in the example of calculation " , has been effectively screened to both sides. Table 4 indicates the efficiency of the light tranmitting plate member as to very uniform diffusion of light which is introduced from the front side edge. Almost all the light is exploited effectively as only l. " 4% of the radiation of light has to be screened at the rearmost side edge if this light has not t.o be exploited also, e.g. by a double sign system. Such a double sign system by way of example may comprise two light transmitting plate members illuminated by lamps from opposite ends so that farthest side edge of both light transmitting plate members may be directly interconnected, whereby also the light radiation from both "farthest" side edges may be effectively exploited. By means of the light transmitting plate member according to the invention in this manner an illuminated sign may have a total length of more than 2000 mm. without the sign needing to be correspondingly extra thick and extra heavy to handle. A further alternative embodiment of the light transmitting plate member according to the invention may consist in that the light transmitter adjacent to the light source, i.e. at the first division, has an extra strongly graduated slope after which the succeeding divisions again have very little graduated slope with successively increasing angles of inclination in the direction receeding from the light source. Such alternative embodiment of the light transmitter according to the invention may advantageously be used in particular cases where one due to certain reasons is forced to use a light source of less efficiency. In such a case it may even be actual to use a light transmitter with increased thickness, e.g. the double thickness, at the front side edge, while the light transmitter already after first division again is of "normal" thickness. For very short and narrow illuminated signs may be used a light transmitting plate member cfr . the invention with a very little initial thickness, e.g. on 5 mm or even less. For the executed tests have been used light transmitting plate members according to the invention which were produced from plane acryl plates by milling and succeeding polishing. However, it is expected that the light transmitting plate member according to the invention in the coming production should be produced by rolling of plane acryl plates or in a material with corresponding light- technical qualities. Furthermore, as has been mentioned, to produce the light transmitting plate member according to the invention by extrusion which presumeably especially would be advantageous for smaller light transmitting plate members. Of course the light transmitting plate member according to the invention may also be produced by casting which by the way is a method which is very often used when producing, plate-scaped items from acryl or similar materials. Preferably the light transmitting plate member according to the invention consists of limpid acryl, but of course nothing would prevent production of the light transmitting plate member as described from tranparent, coloured artificial resin, such as acryl. The introduction of light into the front side edge of the light transmitter may according to a method known per see be improved by providing said side edge with a gradual slope in relation to the plane front side of the light transmitting plate member; or the said side edge thereof may be provided with a very weak curve, i.e. concave, whereby the introduction of rays of light may be more effective. If the foremost side edge portion of the light transmitter is inserted somehow into the lamp housing, it would furthermore be possible to improve the transmission of light through the light transmitting plate member by applying one or both opposite side surfaces thereof with a silvering which of course may not extend outside the lamp housing. Instead of illuminating the light transmitting plate member directly by means of a lamp there may be used more separate light transmitters which are inserted into suitable holes in the foremost side edge and which are supplied with light from a quite separate special lamp which could even be common for more separate light transmitting plate members.

Claims: CLAIMS : 1. A light transmitting plate member for illuminated signs, illuminated tables or a similar illuminated flat item and adapted for uniform diffusion of light from a light source positioned at a side edge of the light transmitter which has a preferable flat side and an opposing side which has a gradual slope, the plate member having a reduced thickness in the direction away from said first side edge, said opposite sides are provided with optically smooth surfaces as the light transmitting plate member consists of transparent and light transparent material with specific optical properties, c h a r a c t e r i z e d in that said side with the gradual slope is provided with a number of angled divisions which are defined by transverse divisional lines which run parallel to said first side edge and which are positioned with either uniform intervals or with graded intervals which are reduced in the direction receeding from said first side edge, in that the height or the thickness of the light transmitting plate member at the transverse divisional lines corresponds to the thickness of the light transmitting plate member at said first side edge, whose angled divisions from said divisional lines and in the direction away from said first side edge have reducing thickness. 2. A light transmitting plate member according to claim 1, c h a r a c t e r i z e d in that the angles of inclination of said angled divisions of said opposite side and the said mutual lengths between said divisional lines are varied in such a manner that each of said angled divisions or gradual slopes are illuminated approximately uniformly by light diffusion from the the respective sides of the light transmitting plate member, of which the said first preferably flat side is considered as the front side of the light transmitting plate member which is preferably turned against the item which is to be illuminated e.g. a sign plate, while said opposite side of the light transmitting plate member with said gradual slopes is considered as the rear side of the light transmitting plate member whereby preferably is positioned a reflector being adapted to reflect the light directly through the light transmitting plate member towards the plane front side thereof. 3. A light transmitting plate member according to claim 1 and 2, c h a r a c t e r i z e d in being provided of a preferably plane acryl plate of little thickness, e.g. 5 - 15 mjn, preferably abt. 10 mm and with a considerable length, e.g. 200 - 1400 mm, preferably abt. 1200 mm, as said angled divisions are varying from abt. 0.1° - 5° nearest at said first side edge to abt. 5° - 20° farthest of from said first side edge - dependent on the total length of the light transmitting plate member.

Inventors: TOFT NILS, TOFT, NILS
Applicants: DANSKE STATSBANER, MOELLER JENSEN JENS, DANSKE STATSBANER DSB, MOELLER-JENSEN JENS
Application year: 1988
Main classification: G09F13
IPC codes: F21V8, G02B6, G09F13