Abstract:
The present invention discloses an edge-lit panel for emergency lighting using dual mode illumination. The panel includes active lighting by the own light source of the equipment and passive lighting by photo-luminescent pigments coated on various surfaces of the panel. Thus, this edge-lit panel provides an improved and extended visibility of electrically energized edge-lit emergency signs during power failures.

Description:
CROSS-REFERENCE TO RELATED PROVISIONAL APPLICATION  
       [0001]     This application claims priority to U.S. Provisional Application No. 60/619,073, filed Oct. 15, 2004. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates generally to lighting sign applications and more specifically to an edge-lit panel with photo-luminescent features to provide illumination even during loss of power to the panel.  
       BACKGROUND OF THE INVENTION  
       [0003]     The edge-lit panels with emergency light signs such as a lighted exit sign are well known in the art. Exit signage using photo-luminescent (PL) materials are becoming more and more popular in the industry. The majority of these products are not internally powered and the PL coating of the legend in the panel is charged in the ambient light. During a power failure the EXIT legend provides passive illumination (glow) for several hours. The main disadvantage of this method is that the performance of the exit sign depends on the ambient light level. Furthermore, the equipment must be installed at a specified distance from a permanent light source, which has to deliver a specified minimum luminance level.  
         [0004]     Other solutions such as in U.S. Pat. No. 6,364,498 use EXIT signs with translucent legends where the PL coating is energized by the equipment&#39;s own light source, and is positioned behind the legend i.e., back-lit. This solution does not need ambient lighting for functioning. It uses a dual mode illumination, the active lighting with its own light source installed behind the display and passive lighting with photo-luminescent pigment coated on the display panel.  
         [0005]     Alternative solutions of EXIT signage for emergency lighting use display panels with the active light source positioned on the edge of the display i.e. edge-lit, instead of back-lit. One such solution is shown and described in a co-pending commonly assigned U.S. patent application Ser. No. 10/898,649, filed Jul. 23, 2004 entitled, “Cold-Cathode Fluorescent Lamp Assembly for Lighting Applications”. This application is incorporated by reference herein for all purposes.  FIGS. 1 and 2  show typical methods of manufacturing edge-lit panels  10  for EXIT signs with a legend  11  and a contour  12 . The light source  13  is applied on the panel edge, perpendicular to the display surface. The display i.e. legend  12  is illuminated as an effect of the multiple reflections  14  and refractions  15  of the light beams on the panel front  10   a  and back surfaces  10   b.  The legend coating  12  is applied either on the back  10   b  of the panel  10  as shown in  FIG. 1  or on the panel front face  10   a  as shown in  FIG. 2 , with this second option allowing for a better background illumination.  
         [0006]     It is thus desirable to provide an improved edge lit panel having improved and extended visibility.  
       SUMMARY OF THE INVENTION  
       [0007]     In one embodiment of the present invention there is provided an edge lit panel including a front side and a back side. The back side includes a frosted clear acrylic surface with a white opaque lamination glued on the frosted surface. A layer of photo-luminescent material is disposed entirely on the back side. A legend is printed on the front side using first and second layers of semi-transparent materials. The first layer is white and second layer is colored.  
         [0008]     In another embodiment of the present invention, there is shown an edge lit panel including a front side and a back side. The back side includes a frosted clear acrylic surface with a white opaque lamination glued on the frosted surface. The legend is printed on the front side using first and second layers of semi-transparent materials. The first layer is white and the second layer is colored. A contour is engraved on the legend on the front side. Also, the photoluminescent material is disposed only on the engraved contour on the front side of the panel.  
         [0009]     In an alternate embodiment of the present invention, there is shown an edge lit panel having a front side and a back side with a legend printed on the backside. The legend includes first and second layers of semi-transparent materials with the first layer being white and the second layer being colored. Also, a contour is engraved on the legend on the back side. The photo-luminescent material is disposed only on the engraved contour on the back side of the panel.  
         [0010]     In another alternate embodiment of the present invention, there is shown an edge lit panel with a front side and a back side with the back side including an opaque lamination. The legend is printed on the back side using first and second layers of semi-transparent materials. The first layer is white and the second layer is colored. Also, the photoluminescent material is disposed only on the legend. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a perspective view of a prior art edge-lit emergency sign with legend coating applied on the back of the panel.  
         [0012]      FIG. 2  is a perspective view of a prior art edge-lit emergency sign with legend coating applied on the front face of the panel.  
         [0013]      FIG. 3  is a perspective view of an edge-lit emergency sign of the present invention with photo-luminescent (PL) layer added on the back of the panel.  
         [0014]      FIG. 4   a  is a perspective view of an edge-lit emergency sign of the present invention with the legend and PL contour engraved on the front of the panel.  
         [0015]      FIG. 4   b  is a perspective view of an edge-lit emergency sign of the present invention with the legend and PL contour engraved on the back of the panel.  
         [0016]      FIG. 5  is a perspective view of an edge-lit emergency sign of the present invention having the PL legend with clear or colored opaque background.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     An edge-lit panel of an emergency sign according to the present invention uses dual mode illumination. One mode is active lighting by the own light source of the equipment and the other mode is passive lighting by photo-luminescent (PL) pigments or material coated on the panel. The PL material is energized by the light source of the equipment. During a power failure, after the equipment back-up power has depleted and its light source has extinguished, the PL-based legend components (text, text contour, and background) will still glow in the dark for several hours, indicating the path of egress, as described in greater detail hereinbelow.  
         [0018]     Referring to  FIG. 3 , there is shown a perspective view of an edge-lit panel emergency sign according to one embodiment of the present invention.  
         [0019]     The edge-lit panel shown in  FIG. 3  is a rectangular shaped panel  30  formed of acrylic plastic or other clear materials. The panel  30  includes a front side  30   a  and a back side  30   b.  The surface of the back side  30   b  may preferably be clear or matted (frosted). The panel  30  also includes side edges, top edge  30   c  and bottom edge  30   d.  A layer of PL material  31  is added on the back side  30   b  of the panel  30 . A white, opaque lamination  32  such as plastic or paper is preferably glued on the PL layer  31  to increase the layer reflectivity.  
         [0020]     The panel  30  further includes a legend  34  including the word “EXIT” printed on the front side  30   a  of the panel  30  by using two consecutive layers  34   a  and  34   b  of semi-transparent materials (screening ink, plastic lamination, etc.). The first layer  34   a  is white and has the role to split the light. The second layer  34   b  is colored with either red, green, blue, etc. A light source  35  is placed at the top edge  30   c  and therefore panel  30  is illuminated from the top edge  30   c  as shown. The light falls from the top edge  30   c  of the panel  30  as shown by straight vertical lines  36 . Part of the light is reflected back into the panel  30  as shown by lines of multiple reflections  37 , thereby energizing the PL  31  on the background. The other part passes through as shown by lines of multiple refractions  38 , and lights the second layer  34   b  of the legend  34 . The second layer  34   b,  is colored and is illuminated by refracted light  38  coming from the panel. With this method, the legend  34  can be internally illuminated, i.e., red looks red in the panel  30  during complete darkness. A legend contour  39  may optionally be engraved on the legend side of the panel  30  as shown in  FIG. 3 .  
         [0021]     The word “EXIT” in the legend  34  is illuminated by the light source  35 . This illumination is reflected in the forward direction through the panel  30  making the “EXIT” sign visible and is also illuminated in the reverse direction to energize the PL  31  in the back side  30   b.  The light source  35  keeps the word “EXIT” in the legend  34  illuminated as long as there is power to the source  35 . However, when the power to the source  35  is cut, the word “EXIT” in the legend  34  remains visible only due to the PL coating  31  on the back side  30   b  serving as a background to the panel  30 . This PL based background will still glow in the dark keeping the word “EXIT” in the legend visible during long lasting power failures.  
         [0022]     Referring to  FIG. 4 , there is shown a perspective view of edge-lit panel  30  emergency sign according to an alternate embodiment of the present invention.  
         [0023]     Specifically in  FIG. 4   a,  the legend  34  including the word “EXIT” is printed on the front side  30   a  using the white layer  34   a  and the colored layer  34   b  as in  FIG. 3 . Also, the contour  39 ′ is engraved on the word “EXIT” in the legend  34 , also on the front side  30   a.  This engraving contour  39 ′ is coated with PL material  31 . Additionally, similar to  FIG. 3 , the back side  30   b  of the panel  30  also includes an opaque lamination  32  preferably glued on the backside  30   b.    
         [0024]     The light source  35  at the top edge  30   c  of the panel illuminates the word “EXIT” in the legend  34 . However, during power failure of the source  35 , the word “EXIT” in the legend  34  remains visible only due to the PL coating  31  on the contour  39 ′. This PL based text contour glows in the dark keeping the outline of the word, “EXIT” visible during long lasting power failures.  
         [0025]     In  FIG. 4   b,  the legend  34  including the word “EXIT” is printed on the back side  30   b.  Also, the contour  39 ″ is engraved about the legend  34  on the back side  30   b.  This engraving contour  39 ″ is coated with PL material  31 . Also, preferably the white reflective layer  32  is applied on the back side  30   b  of the panel  30  as shown. The light source  35  at the top edge  30   c  of the panel illuminates the word “EXIT” in the legend  34 . This illumination is reflected forwardly through the panel  30  making the “EXIT” sign visible and is reflected back to energize the PL coating  31  in the contour  39 ″. During the power failure of the source  35 , this PL based text contour glows in the dark keeping the outline of “EXIT” visible.  
         [0026]     Referring to  FIG. 5 , there is shown a perspective view of edge-lit panel according to an alternate embodiment of the present invention. The legend  34 ′ including the word “EXIT” is printed on back  30   b  of the panel  30  and coated with the PL material  31 . Preferably a layer of clear or colored opaque lamination  32  is glued on the back side  30   b  of the panel  30 . Again the contour  39  may optionally be engraved on or about the legend  34 ′, and also on the back side  30   b  of the panel  30 .  
         [0027]     The word “EXIT” in the legend  34 ′ is illuminated by the light source  35 . This illumination is reflected in the forward direction through the panel  30  making the word “EXIT” in the legend  34 ′ visible in the front side  30   a.  The source  35  also illuminates in the reverse direction to energize the PL  31  in the legend  34  in the back side  30   b.  The light source  35  keeps the word “EXIT” in the legend  34 ′ illuminated as long as there is power to the source  35 . However, when the source  35  is cut, the word “EXIT” in the legend  34 ′ remains visible only due to the PL coating  31  on the legend  34 ′ itself. This PL based legend will still glow in the dark keeping the word “EXIT” visible long after a power failure.  
         [0028]     Therefore, in the present invention, the photoluminescence material can be operatively coupled with an active illumination means, to provide fail-safe illumination when the active lighting elements fail or are interrupted in operation. The invention thus combines a passive illumination means (photoluminescence) with an active illumination means (powered lighting source), in such a way that operational efficacy of the passive system is assured in the event of loss or interruption of the normal operation capability of the active system.  
         [0029]     Photo-luminescent materials are well known in the art, and include for example strontium oxide aluminate, zinc sulfide, calcium sulfide, and strontium sulfide. The intensity of illumination provided by photo-luminescent materials begins to decay immediately upon the removal of ambient or charging light. However, human visual perception increases shortly after the removal of ambient light, as physiological adjustments occur to the eye, and individuals progress to the achievement of “night vision.” Thus, photo-luminescent materials may provide sufficient luminous energy to a sign to render it readable for several hours following the removal of ambient or powered light.  
         [0030]     The active lighting means in the illumination device of the present invention may be of any suitable type and configuration that sufficiently illuminate the display in low or no ambient light conditions. Such active lighting source may comprise, for example, incandescent bulbs, LEDs, fluorescent tubes, electroluminescent lamps, or combination thereof.  
         [0031]     The active lighting source may be positioned in any location that suitably illuminates both the display and the photo-luminescent material. In a preferred embodiment, the active lighting source may be placed on the top of the panel as discussed above. The active lighting source may be powered by any appropriate configuration of power supply and wiring or other energizing circuitry, as are well known in the art associated with the respective active lighting element types.  
         [0032]     While the particular embodiments of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the teachings of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.