Abstract:
A hybrid photoluminescent display consumes little electrical power and provides for light emission/color in a desired color. The display includes a housing having openings forming a desired legend. White LEDs internal to the housing provide light for energizing photoluminescent material. A legend panel housed within the housing defines openings corresponding to the legend. Photoluminescent material is disposed within the openings of the legend panel. The photoluminescent material is selected to be energizable by light from the white light source, and to emit light primarily in a selected wavelength range corresponding to a desired legend color. A color is filter disposed adjacent the photoluminescent material on a side of the legend panel opposite the light source. The color filter is selected to selectively transmit substantially all light in the selected wavelength range, and to selectively not transmit substantially all light outside the selected wavelength range.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority, under 35 U.S.C. §119(e), of U.S. Provisional Patent Application No. 62/006,648, filed Jun. 2, 2014, the entire disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to illuminated displays, and more particularly to an illuminated display having illumination components providing multiple modes of efficient illuminated operation with enhanced performance in a selected band of the visible light spectrum. 
       BACKGROUND OF THE INVENTION 
       [0003]    As used herein, the term “display” is intended to broadly encompass any informational, pictorial or graphic displays, e.g., containing alphabetic and/or numeric text, graphic components, icons, symbols or other visually discernable indicia. These displays may be used in various contexts as signs, panels or any other visual display. One specific and non-limiting example of such a display is a fixed-image sign for emergency lighting purposes, such as an EXIT sign used to indicate an exit or egress path from a building in the context of commercial building construction. Other examples include informational displays in a variety of other locations and/or contexts different from emergency lighting, such as displays indicated “LASER IN USE,” “AREA OF RESCUE ASSISTANCE,” “MRI ON,” or “ON THE AIR.” 
         [0004]    In the specific context of signs for emergency lighting, building codes, transportation safety codes, and/or other regulations require such signs to be plainly visible and to be illuminated at all times when a building is occupied. 
         [0005]    Certain emergency lighting signs include internal energy/light sources powered by building/mains power. With respect to common incandescent, neon, and fluorescent light sources, such essentially continuous illumination is expensive and inefficient. 
         [0006]    Standard photoluminescent emergency lighting signs are commonly available that do not contain an internal energy source, but require a continuous source of ambient light to provide adequate activation when building/mains power is available. This is typically provided from a lighting fixture mounted in close proximity to the photoluminescent exit sign, which in many cases requires a costly and high power consuming installation primarily required to activate the emergency lighting sign as well as periodic maintenance to ensure adequate activation. 
         [0007]    Such ambient light-based systems are susceptible to downtime due to power failures in the electrical power grid. To provide illumination in the event of building power failure, some hybrid signs have been developed to provide multiple illumination modes. Such hybrid photoluminescent signs typically consist of a code-approved legend illuminated by an internal energy source that provides required illumination for a means of egress from an internal source when building/mains power is available, and from an afterglow from photoluminescent material that has been activated from said internal source after mains power becomes unavailable. 
         [0008]    U.S. Pat. Nos. 6,364,498, 6,843,010 and 7,412,790 disclose exemplary signs with multiple illumination modes. For example, U.S. Pat. No. 6,364,498 discloses a sign that uses a powered light source to illuminate lettering/characters and to energize photo-luminescent pigment during normal operation. The pigment glows and thereby illuminates the lettering in the event of a power failure. 
         [0009]    Alternatively, some signs have been developed to include battery backup systems. However, battery backup systems have several limitations and/or disadvantages, including that they consume power essentially all of the time, which is still further expensive and inefficient. In addition, batteries have limited lives, and thus require periodic testing of the sign and frequent battery replacement, which has a resulting adverse environmental impact. 
         [0010]    To address the inefficiency of battery backup systems and/or signs with incandescent or other light sources, some energy efficient signs have been developed that use energy-efficient LEDs as the light source. U.S. Pat. Nos. 7,937,865, 8,302,336, 8,539,702, and 6,883,926 disclose exemplary signs using LEDs as a light source. 
         [0011]    Unlike energy inefficient incandescent, neon and fluorescent light sources that produce white (broad visible spectrum) light, many energy-efficient LEDs do not generate white light. In the context of exit signs, the desired color is most often red (625 nm) or green (520 nm). Though energy-efficient, many LEDs are objectionable in that provide undesirably low radiative performance in the desired color spectrum, and/or undesirably high radiative performance outside the desired color spectrum. 
         [0012]    What is needed is an illuminated display comprising having illumination components providing multiple modes of efficient illuminated operation, while also provide enhanced radiative performance in a selected band of the visible light spectrum, such as the red or green spectrum for emergency lighting signs. 
       SUMMARY 
       [0013]    The present invention provides a hybrid photoluminescent display that consumes very low electrical power, e.g., approximately 0.5 watts, and also provides activation of internal photoluminescent material during the period when mains power is available, thereby not require a source of ambient light. In addition, the present invention allows for use of white LEDs while also providing for a legend color in a desired color/wavelength range. In the context of exit signs, the present invention can provide red or green light emission, as is commonly used in exit signs, along with a high contrast ratio against the housing face, when the sign is unpowered and viewed by ambient light. 
         [0014]    In one exemplary embodiment a hybrid photoluminescent display for displaying a visually-perceptible legend in a desired legend color includes an outer housing comprising first and second shells constructed of an optically opaque material. The shells are matable to define an enclosure. At least one of the first and second shells defines a plurality of openings collectively forming the legend. Each shell has a respective inner surface, and the outer housing defines at least one rib. 
         [0015]    A light source comprising a plurality of white light emitting diodes (LEDs) is configured to emit white light across a broad wavelength spectrum when energized by an electrical power source. 
         [0016]    A legend panel is dimensioned for receipt within the outer housing. The legend panel comprises a rigid substantially planar member of a first material. The planar member defines a plurality of openings corresponding to the plurality of openings in the outer housing that collectively form the legend. The plurality of openings are positioned to align with the openings when the legend panel is captured within the outer housing between the rib and the respective inner surface of the shell(s). 
         [0017]    Photoluminescent material is disposed within each of the plurality of openings of the planar member to provide a substantially planar and continuous legend panel. The photoluminescent material is selected to be energized by light from the white light source, and to emit light primarily in a selected wavelength range corresponding to a desired legend color. 
         [0018]    A color filter is disposed adjacent the photoluminescent material opposite the light source. The color filter is selected to selectively transmit substantially all light in the selected wavelength range, and to selectively not transmit substantially all light outside the selected wavelength range. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention will now be described by way of example with reference to the following drawings in which: 
           [0020]      FIG. 1  is a front elevational view of an exit sign in accordance with an exemplary embodiment of the present invention; 
           [0021]      FIG. 2  is a front perspective view of the exit sign of  FIG. 1 ; 
           [0022]      FIG. 3  is a front view of the components of the exit sign of  FIG. 1 ; 
           [0023]      FIG. 4  is a top view showing a legend template including cast luminescent material; 
           [0024]      FIG. 5  is an enlarged view of an interior portion of an enclosure of the exit sign of  FIG. 1 ; 
           [0025]      FIG. 6  is a front view of the components of the exit sign of  FIG. 1 , showing the color filter and legend panel assembled to the front shell  24 ; 
           [0026]      FIG. 7  is a front view of the components of the exit sign of  FIG. 1 , showing the color filter and legend panel partially assembled from the front shell  24 ; and 
           [0027]      FIG. 8  is a front view of the components of an alternative exit sign that is similar to that of  FIG. 1 , but showing an alternative housing having a double-face construction in which both the front and rear shells including openings for displaying a legend, and in which the sign further includes a second legend panel and color filter assembled to the rear shell  22 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    A hybrid photoluminescent display is discussed in the context of an exemplary exit sign suitable for use as emergency lighting in building construction applications. It should be noted that this discussion in the context of emergency lighting, and in particular as an exit sign, is for non-limiting illustrative purposes only. The inventive display may have any suitable configuration for any suitable application, context, or environment. 
         [0029]    Referring now to  FIGS. 1-7 , the exemplary display sign  100  includes an outer housing  20 , an LED light source,  40 , a legend panel  60 , and a color filter  70 , as best shown in  FIGS. 1-3 . 
         [0030]    As best shown in  FIGS. 2 and 3 , the outer housing  20  is constructed of an optically opaque material, and includes separate shells matable to one another to form a substantially-enclosed outer housing  20 . By way of example, the housing may be molded from a die cast aluminum or a flame retarding (class I) polymeric material such as, but not limited to, polycarbonate, or ABS. 
         [0031]    In the exemplary embodiment, the outer housing  20  includes a rear shell  22  matable to a front shell  24 . A portion of the outer housing, in this case the front shell  24 , is configured to define a plurality of openings that collectively define or otherwise form the intended visually perceptible legend of the sign  100 . In this exemplary sign, the openings  26   a,    26   b,    26   c,    26   d,    26   e,    26   f  collectively form a legend including the word EXIT and a pair of chevron-shaped graphical elements. However, it should be appreciated that any suitable configuration of one or more openings may be used to provide the desired legend in accordance with the present invention. 
         [0032]    Further, in this exemplary embodiment, the housing  20  includes hinge members  28  pivotably interconnecting the rear and front shells  22 ,  24 , as best shown in  FIGS. 3 and 5 , so that the shells can pivot between an open position (similar to that shown in  FIGS. 3 and 5 , and a closed position in which the shells  22  and  24  abut one another to form the substantially-enclosed outer housing, as shown in  FIGS. 1 and 2 . 
         [0033]    Further, in this exemplary embodiment, the housing  20  further includes catch members  30 . The catch members  30  are configured to releasably retain the front and rear shells  22 ,  24  in the closed position. In this exemplary sign, each catch member  30  is comprised of a resiliently deflectable body that is configured to abut, deflect, and ride over a projection of the mating shell, and then to resile to cause the body to interfere with the projection and thereby retain the shells  22 ,  24  in the closed position. 
         [0034]    The housing  20  is further configured to support the light source  40 . In accordance with the present invention, light source  40  comprises one or more white light emitting diodes (“LEDs”)  42 , which are selected for both their energy efficiency and their admission of a broad spectrum of visible light, i.e., “white” light. As is well-known in the art, white LEDs include photoluminescent material that absorbs a portion of the radiation emitted by the LED and re-emits radiation of a different color (wavelength), so that the light emitted by the LED and re-emitted by the photoluminescent material collectively provide a combination of blue, red, green, and yellow light, which in combination provides “white” (broad visible light spectrum) light, that generally appears to the human eye as being “white.” The light source preferably includes a plurality of individual white LEDs  42  physically supported in roughly-equal spaced relationship on a substrate  44  that is in turn mounted on bosses or other supports  32  of the housing, as best shown in  FIGS. 3 and 5 . Preferably, the substrate  44  is supported along one of the long sides of a rectangular housing  20 . The light source further includes electrical wiring  46 , an electronic driver circuit  48  for supplying appropriate current and/or voltage to the LED&#39;s, and or other components necessary to cause illumination of the LEDs when the light source is connected to and receiving electrical power from a building&#39;s AC or other electrical power system. Accordingly, the display/sign also includes an electrical conductor  50  operably connected to the light source and extending outwardly of the housing. 
         [0035]    Referring now to  FIGS. 3 and 4 , the exemplary display  100  further includes a legend panel  60 . Legend panel  60  is a substantially flat/planar member, constructed of a rigid sheet  64  such as a polycarbonate, ABS, or acrylic, that is configured to define a plurality of openings  62   a,    62   b,    62   c,    62   d,    62   e,    62   f,  each of which is configured, sized and positioned to correspond to the openings in the housing. By way of example, the panel may be molded or machined to include such openings. Accordingly, in this example, the plurality of openings collectively forms a legend including the word EXIT and a pair of chevron-shaped graphical elements. Preferably, the openings in the rigid sheet  64  are as large as or larger than the openings in the housing, so as to be coextensive with (or larger than) the openings in the housing. Within these openings is provided photoluminescent material, e.g., via a casting or molding process, to provide corresponding photoluminescent characters  66 . Accordingly, the legend panel  60  is substantially planar and continuous, as will be appreciated from the front and rear sides of the legend panel, two legend panels being shown in  FIG. 4 . A legend panel  60  is dimensioned to be received within the outer housing  20 , and to abut support structures consisting of side walls  32  and ribs  34  within the outer housing such that when the shells of the outer housing are in the closed position, legend panel  60  is captured and fixedly supported between the shells  22 ,  24 , as will best appreciated from  FIG. 6 . Thus, the legend panel  60  is mountable in the outer housing  20  with the photo-luminescent character(s) disposed adjacent to an inner surface of the first front shell  24 .  FIG. 6  is a front view of the components of the exit sign of  FIG. 1 , showing the legend panel  60  assembled to the front shell  24 . 
         [0036]    Any suitable photoluminescent material may be selected for this purpose. However, it is preferable to select a photoluminescent material that will emit light in a wavelength range corresponding to the light desired to be emitted from the sign. In the context of exit signs, red and green light emission from the sign is often preferred. In this example, green light emission from the exemplary exit sign green is preferred. 
         [0037]    Many current photoluminescent exit signs use strontium aluminate photoluminescent material, which typically has excitation and emission spectra as shown in Table 1 below. 

 
         [0038]    InGaN LEDs with YAG phosphors are commonly available to produce white light, and are a preferred choice for exciting this photoluminescent material. These LEDs are generally energy-efficient, have a lifetime in excess of 50,000 hours, include useful areas of the spectrum for this application, and do not produce UV radiation in the range damaging to humans and/or polymer materials. 
         [0039]    The spectral characteristic shown below in Table 2 is associated with an exemplary InGaN LED that is suitable for this application. 

 
         [0040]    In this example, the peak Relative Emission Intensity of 450 nm provides an efficient source for providing excitation for the strontium aluminate photoluminescent material. In addition, there is adequate emission in range of visible green (520 nm) to provide desirable green legend color while mains power is available. 
         [0041]    However, utilization of InGaN LEDs with YAG phosphors as the light source, without correction, provides undesirable effects for sign for which green light emission is desired. Particularly, with building power available, the 450 nm energy, while efficiently activating the strontium aluminate photoluminescent material, also bleeds through the photoluminescent material, creating a “royal blue” color effect to light emitted from/through the legend panel, and thus the display sign, which is undesirable when the desired sign color is green. 
         [0042]    In addition, the 600 nm energy and above, also bleeds through the photoluminescent material, creating yellow and red color effects to light emitted from/through the legend panel, and thus the display sign, which is undesirable when the desired sign color is green. 
         [0043]    Accordingly, in accordance with the present invention, the display  100  further includes a color filter  70 , as best shown in  FIG. 3 . The color filter is selected to provide specific spectral energy transmittance characteristics to selectively block/absorb light outside the desired color range, and to selectively transmit light within the desired color range. 
         [0044]    In one embodiment, the color filter  70  is a separate polycarbonate or polyester film produced by co-extruding or surface coating with appropriate dyes, or screen printing with transparent color pigments. In the assembled sign, the color filter is sandwiched between the legend panel  60  and the portion of the outer housing  20  including the openings providing the legend, and thus is captured and supported therebetween. 
         [0045]    In an alternative embodiment, the color filter  70  comprises a layer of transparent pigment, having the appropriate spectral characteristics, applied to the surface of the legend panel  60 , in particular, over the photoluminescent material/characters. By way of example, this layer of transparent pigment may be applied by a screen printing process, though any suitable process may be used. In either case, the color filter  70  is positioned on a side of the legend panel  60  opposite the light source  40 . 
         [0046]      FIG. 7  is a front view of the components of the exemplary exit sign of  FIG. 1  shown partially disassembled to show the color filter  70  between the legend panel  60  and front shell  24 . 
         [0047]    In the context of the exemplary exit sign discussed above that employs InGaN LEDs with YAG phosphors as the light source and strontium aluminate as the photoluminescent material in the legend panel  60 , and for which green light emission is desired from the sign, it is therefore desirable to block both the 450 nm energy (blue) and below, and the 600 nm and above (yellow and red energy) from exiting the photoluminescent legend panel  60 , and also to allow emission of 500 nm energy (green) from the photoluminescent legend panel  60 , to provide for an essentially green light emission from the sign. 
         [0048]    Accordingly, a color filter  70  may be used having the desired specific spectral energy transmittance characteristics. For example, polycarbonate color filters in thin film form are commercially available from Lee Filters USA of Burbank, Calif. that provides various spectral energy transmittance characteristics. For the particular example discussed herein, Lee Filters&#39; polycarbonate color filter no. 122 is appropriate and provides the specific spectral energy transmittance characteristics shown below in Table 3. 

 
         [0049]    Accordingly, for this exemplary color filter  70 , the transmittance at 450 nm (blue) is approximately less than 5% thereby attenuating the peak “royal blue” energy viewed from the face of the sign. Further, the transmittance at 600 nm and above (yellow/red) is approximately an average of about 10% thereby attenuating the yellow and red energy viewed from the face of the sign. Further, the transmittance at 500 nm is approximately 80%, thereby causing just a modest loss of green energy emission of the photoluminescent material when viewed from the face of the sign. 
         [0050]    When viewed by white reflected ambient light, and powered from mains, these characteristics produce the desired dark green (in this example) color to the legend, which is preferred in exit signs. Further, this exemplary arrangement provides a high contrast ratio against a light-colored/white-colored outer housing, even when building power is available, and under ambient light conditions. 
         [0051]    It will be appreciated that different photoluminescent materials in the legend panel  60  and different color filters with different spectral energy transmittance characteristics can be combined with the use of white LEDs to provide for other signs having other desired emission wavelength ranges—e.g., to provide essentially blue, yellow, red, etc. displays. 
         [0052]    When assembled, the display  100  includes the legend panel  60  and color filter  70  supported within the outer housing  20 , namely, between the rear shell  22  and light source  40 , and the shell  24 . 
         [0053]      FIG. 8  is a front view of the components of an alternative exit sign that is similar to that of  FIG. 1 , but showing an alternative housing  20  having a double-face construction in which both the front and rear shells  22 ,  24  include openings (similar to those shown above in reference to the front shell) for displaying a legend, and in which the sign further includes a second legend panel and color filter assembled to the rear shell  22  in a manner similar to that described above with reference to the front shell. Accordingly, the sign&#39;s legend is visible from the front and back of the display. 
         [0054]    In operation, when building/mains power is available, white light emitted by the energy-efficient white LEDs irradiates the photoluminescent material of the legend panel  60 , causing excitation of the photoluminescent material and emission of light from the photoluminescent material of the legend panel  60 . In this example, the photoluminescent material emits green light as well as white light from the LEDs that has bled through the photoluminescent material. This white/broad visible spectrum light emitted from the legend panel  60  then passes through the color filter  70 , which is selected to transmit only light of a desired color, blocking/absorbing undesirable royal blue, yellow and red radiation from the LEDs, resulting in visible green color which is preferred in exit signs, without reducing the effectiveness of activating the photoluminescent material by the radiation of the LEDs. When building/mains power is not available, the display further provides an afterglow in the desired color rage from photoluminescent material that has been activated by the LEDs during normal operation. 
         [0055]    While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. While there have been described herein the principles of the invention, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation to the scope of the invention, and that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.