Internally illuminated sign

Abstract

An illuminated sign, internally illuminated by a source such as one or more LED'S generally located at one end, and having a character panel with at least partially transmissive portions to define the characters of the sign. The character panel is curved so as to face the source more squarely at distances further from the source. By this arrangement, the geometric fall-off of illumination with increasing distance from the source is compensated for by the curvature of the character panel, such that more uniform illumination is provided than with prior art flat panels. Power management systems for solar charged illuminated signs are also described, in which the illumination level of the sign is adjusted according to the ambient solar flux and according to the charge-holding capacity of the battery. The system also warns of the impending end of battery life without interrupting the sign functionality.

1 . An internally illuminated sign, comprising:
 at least one source of light; and   at least one display surface illuminated by said light and comprising regions generally opaque to said light and regions diffusively transmissive to said light, said diffusively transmissive regions forming at least one character to be displayed by said sign,   wherein said at least one source of light is mounted such that said light is directed at said at least one display surface at close to a glancing angle, and said at least one display surface has a curved contour, concave to said at least one source, and such that light from said at least one source impinges on said display surface at an angle of incidence which varies according to the distance of the point of impingement of said light from said light source.   
   
   
       2 . An internally illuminated sign according to  claim 1 , wherein said curved contour reduces variations in the luminous flux per unit area of said light impinging on said at least one display surface, in comparison with variations in said luminous flux per unit area impinging on a non-curved display surface. 
   
   
       3 . An internally illuminated sign according to  claim 1  and further comprising at least one reflective surface disposed adjacent said at least one display surface, and reflecting light towards said at least one surface. 
   
   
       4 . An internally illuminated sign according to  claim 1 , further comprising a second display surfaces illuminated by said light. 
   
   
       5 . An internally illuminated sign according to  claim 1 , wherein said curved contour is shaped such that the luminous flux per unit area of said light impinging on said at least one display surface is essentially independent of the distance of the point of impingement of said light from said at least one light source. 
   
   
       6 . An internally illuminated sign according to  claim 1 , wherein the side of said generally opaque regions of said at least one display surface facing said at least one source of light comprises a reflective layer, such that said light not transmitted through said at least partly transmissive regions of said one display surface is reflected back into said sign. 
   
   
       7 . An internally illuminated sign according to  claim 4 , and further comprising at least one reflective surface having a curved contour, convex to said at least one light source, and disposed between said two display surfaces illuminated by said light. 
   
   
       8 . An internally illuminated sign according to  claim 1 , wherein said at least one source of light comprises at least one light emitting diode. 
   
   
       9 . An internally illuminated sign according to  claim 6 , wherein said at least one display surface comprises:
 a reflective metallic layer, on which is formed a generally opaque coating defining a negative of the shape of said character, such that said character defines a clear area over said reflective metallic layer, said clear area being a mask for the removal of said reflective metallic layer in the region of said character.   
   
   
       10 . An internally illuminated sign according to  claim 1 , further comprising at least one rechargeable battery for powering said at least one source of light, and at least one solar cell for recharging said rechargeable battery. 
   
   
       11 . An internally illuminated sign according to  claim 9 , wherein said at least one display surface is produced by a method comprising the steps of:
 forming said character on said reflective metallic layer by means of a generally opaque coating applied around said character shape, such that said character defines a clear area over said reflective metallic layer; and   removing said reflective metallic layer in the region of said character, using said clear area as a mask.   
   
   
       12 . An internally illuminated sign according to  claim 1 , wherein said at least one source of light is disposed adjacent an end of said at least one display surface. 
   
   
       13 . An internally illuminated sign according to  claim 1 , wherein said at least one source of light comprises a plurality of light sources disposed in the central region of said at least one display surface, at least two of said plurality of light sources pointing in essentially opposite directions, such that said sign is double-ended. 
   
   
       14 . A method of improving the uniformity of illumination on at least one display surface of an internally illuminated sign, comprising the steps of:
 providing at least one source of light for illuminating said at least one display surface;   providing said display surface with a curved contour; and   directing said light at said display surface at close to a glancing angle, such that said curved contour reduces variations in the luminous flux per unit area of said light impinging on said at least one display surface, in comparison with variations in said luminous flux per unit area impinging on a corresponding non-curved display surface.   
   
   
       15 . A method according to  claim 14  and wherein said curved contour is shaped such that said luminous flux per unit area of said light impinging on said at least one display surface is essentially independent of said distance of the point of light impingement from said at least one source. 
   
   
       16 . A method according to  claim 15  and wherein said curved contour is determined by a method comprising the steps of:
 dividing said at least one display surface into areas according to the distance of said areas from said source;   determining the illumination falling on a first area of said at least one display surface as a function of the distance of said area from said at least one source and the angular orientation of said area relative to the direction to said at least one source;   determining the distance of a second area of said display surface from said at least one source; and   calculating the angular orientation required of said second predefined area of said at least one display surface such that said first and said second predefined areas of said screen receive essentially the same illumination.   
   
   
       17 . An electronic system for a solar charged, battery operated, illuminated sign, comprising:
 a solar panel providing an output in accordance with the solar illumination incident thereon;   at least one light source for illuminating said sign;   at least one battery chargeable by said output, for supplying current to said at least one light source, said at least one battery providing a voltage dependent on the state of said charge of said at least one battery; and   a controller programmed to control said current at least in accordance with said voltage, such that said current is reduced when said voltage falls below a first predetermined level.   
   
   
       18 . An electronic system according to  claim 17  and wherein said current is reduced to a level dependent on the level of said voltage below said first predetermined level. 
   
   
       19 . An electronic system according to  claim 17  and wherein said controller is further programmed to pass said current in an intermittent mode when said voltage falls below a second predetermined level less than said first predetermined level. 
   
   
       20 . An electronic system according to  claim 19  and wherein said intermittent mode is operative to indicate that said at least one battery requires replacement.