Illumination device for simulation of neon lighting

An illumination device for simulating neon lighting comprising a plurality of spaced point light sources positioned adjacent a lateral light receiving surface of a substantially rod-like waveguide made of a material that preferentially scatters light entering the light receiving surface such that the light intensity pattern exiting a lateral light emitting surface of the waveguide has a substantially uniform light intensity pattern.

BACKGROUND OF THE INVENTION

The present invention relates to illumination devices using optical waveguide and, more particularly, to lighting devices for the simulation of neon lighting using optical waveguides and high intensity low voltage light sources and ideally adapted for signage and advertising uses.

Neon lighting, produced by the electrical stimulation of the electrons in the low pressure neon gas filled glass tube, has been a main stay in advertising and for outlining channel letters and building structures for many years. A characteristic of neon lighting is that the tubing encompassing the gas has an even glow over its entire length irrespective of the viewing angle. This characteristic makes neon lighting adaptable for many advertising applications including script writing and designs because the glass tubing can be fabricated into curved and twisted configurations simulating script writing and intricate designs. The even glow of neon lighting being typically devoid of hot spots allows for advertising without visual and unsightly distractions. Thus, any illumination device that is developed to duplicate the effects of neon lighting must also have axially even light distribution over its length and substantially even about its circumference. Equally important, such lighting devices must have a brightness that is at least comparable to neon lighting. Further, since neon lighting is a well established industry, a competitive lighting device must be light in weight and have superior “handleability” characteristics in order to make inroads into the neon lighting market. Neon lighting is recognized as being fragile in nature. Because of the fragility and heavy weight primarily due to its supporting infrastructure, neon lighting is expensive to package and ship. Moreover, it is extremely awkward to initially handle, install, and/or replace neon lighting structures. Any lighting device that can provide those previously enumerated positive characteristics of neon lighting while minimizing its size, weight, and handleability shortcomings will provide for a significant advance in the lighting technology.

U.S. Pat. No. 4,891,896 issued on Jan. 9, 1990 to Boren and assigned to the Gulf Development Company is an example of many attempts to duplicate neon lighting. Like this attempt, most prior art neon simulations have resulted in structures difficult to fabricate and providing a little in the way of weight and handling benefits. The Boren patent exemplifies this by providing a plastic panel with essentially bas-relief lettering. The material comprising the lettering is transparent and coated with a translucent material. The surrounding material is opaque. When the panel is back lit the lettering tends to glow with a neon-like intensity.

The more recent introduction of light weight and breakage resistant point light sources as exemplified by high intensity light emitting diodes (“LEDs”) have shown great promise to those interested in illumination devices that may simulate neon lighting and have stimulated much effort in that direction. However, the twin attributes of neon lighting, uniformity and brightness, have proven to be difficult obstacles to hurdle as such attempts to simulate neon lighting have largely been stymied by the tradeoffs between light distribution to promote the uniformity and brightness. For example, U.S. Pat. No. 4,976,057 issued Dec. 11, 1990 to Bianchi describes a device that includes a transparent or translucent hollow plastic tubing which is mounted in juxtaposition to a sheet of material having light transmitting areas that are co-extensive to the tubing. The sheet is back lit by light sources such as LEDs which trace the configuration of the tubing. The tubing can be made into any shape including lettering. While the tubing may be lit by such arrangement, the light transfer efficiencies with such an arrangement is likely to result in a “glowing” tube having insufficient intensity to match that of neon lighting. The use of point light sources such as LEDs may provide intense light that rival or exceed neon lighting, but when arranged in arrays lack the uniformity needed and unfortunately provide alternate high and low intensity regions in the illuminated surfaces. Attempts to smooth out the light has resulted in lighting that has unacceptably low intensity levels.

It is therefore a paramount object of the present invention to provide for an energy efficient, virtually unbreakable alternative to neon lighting.

A further important object of the present invention is to provide for a lighting device that is safe to transport and economical to operate while providing all of the application virtues of neon lighting including uniformity and brightness.

Yet another object of the present invention is to provide for an alternative to neon lighting that is environmentally friendly, requiring no neon gas, and running on significantly less electricity that its neon equivalent.

Still another important object is to provide for a neon equivalent that is easy to install without complex high voltage electrical installations.

Yet a further object is to provide for a lighting device that can be placed in hostile environments such as in a freezer case without need for protective guards against accidental contact by customers.

These and other objects of the invention will become readily apparent and addressed through a reading of the discussion below and appended drawings.

SUMMARY OF THE PRESENT INVENTION

The present invention utilizes a profiled rod of material having waveguide characteristics that preferentially scatters light entering one lateral surface (“light receiving surface”) so that the resulting light intensity pattern emitted by another lateral surface of the rod (“light emitting surface”) is elongated along the length of the rod. A light source extends along and is positioned adjacent the light receiving surface and spaced from the light emitting surface a distance sufficient to create an elongated light intensity pattern with a major axis along the length of the rod and a minor axis that has a width that covers substantially the entire circumferential width of the light emitting surface. In a preferred arrangement, the light source is a string of point light sources spaced a distance apart sufficient to permit the mapping of the light emitted by each point light source into the rod so as to create elongated and overlapping light intensity patterns along the light emitting surface and circumferentially about the surface so that the collective light intensity pattern is perceived as being uniform over substantially the entire light emitting surface when being viewed from a normal head-on and side perspectives.

DETAILED DESCRIPTION OF THE INVENTION

To provide the desired result, i.e., an illumination device that is an effective simulator of neon lighting, it is important that the proper materials be selected for the component parts and those parts appropriately and geometrically positioned so that the resulting illumination device has an essentially uniform light intensity distribution pattern over the entire surface with the maximum obtainable brightness. To accomplish this, it is necessary to use a high intensity but dimensionally small light source together with an element that acts both as an optical waveguide and light scattering member, but permits light to exit laterally out of its surface (a “leaky waveguide”). By placing the light source contiguous such a leaky waveguide in a specific manner so as to cause the waveguide to uniformly glow over its lateral surface while maximizing the amount of light exiting the surface, applicants are able to obtain an illumination device that rivals or surpasses the uniform glow of neon tubing. There are many light sources which have the necessary light intensity output that is required but most are dimensionally too big to be practical, are fragile, or consume too much energy. It has been further observed that the best light source would likely be one with a small diameter that provided a uniform light output over an extended length. However, such light sources have not yet been developed to the technological state providing the intensity needed. Thus, applicants have determined that the best available light source for the purpose here intended is a string or strings of contiguously mounted, essentially point light sources such as spaced apart high intensity LEDs.

The ultimate objective of the illumination device of the present invention is to simulate an illuminated neon tube that glows with the proper intensity and uniformity over its length. Thus, applicants have determined that it is important that the leaky waveguide (used to simulate the neon tube) be comprised of a profiled rod of material having sufficient diffusivity that collectively with the other components of the invention visually eliminates any recognizable individual light distribution light pattern that originates from a respective LED or other light source. As stated above, the profiled waveguide preferentially scatters light along its length but ultimately allows light to exit through its lateral surfaces. Such a waveguide provides a visible elongated or oval-like light pattern for each LED, brightest at the center and diminishing continuously out from the center along the major and minor axis of the pattern. By spacing the LEDs a certain distance apart and each LED an appropriate distance from the exposed and lateral far side of the leaky waveguide, the light intensity distribution patterns on the surface of far side of the leaky waveguide are caused to overlap to such an extent that the variations in the patterns are evened out. This causes the collective light pattern on the lateral surface to appear to an observer to have an uniform intensity along the length of the waveguide. Other components of the illumination device of the present invention including, for example, the shape of the light sources may assist in establishing the required brightness and uniformity.

Structurally, the preferred embodiment of the present invention is portrayed inFIGS. 1-6and shown generally as character numeral10. The device10may be considered as having two major body components. The first component is a waveguide12having an exposed curved lateral surface13serving as the light emitting surface and a hidden lateral surface15(best seen inFIG. 3) that serves as the light receiving surface. Waveguide12is the aforementioned leaky waveguide and surface13serves as the counterpart to the neon tube. That is, the light laterally entering the waveguide from a light source juxtaposed to the surface15is preferentially scattered so as to exit with a broad elongated light intensity distribution pattern out of surface13. Visually, the waveguide12, when not illuminated internally, has a milky appearance due to the uniform scattering of ambient light that enters the waveguide and that ultimately exits the lateral surface thereof. Applicants have found that acrylic material appropriately treated to scatter light and to have high impact resistant to be the preferred material for use in forming the waveguide components of the present invention. When shaped into the profiled rods, the rods take on the desired leaky waveguide characteristics. Moreover, such material is easily molded or extruded into rods having the desired shape for whatever illumination application may be desired, is extremely light in weight, and withstands rough shipping and handling. While acrylic material having the desired characteristics is commonly available, it can be obtained, for example, from AtoHaas, Philadelphia, Pa. under order number DR66080 with added frosted characteristics. When shaped into a rod, such acrylic material is observed to have the leaky waveguide characteristics desired. Other materials such as such as beaded blasted acrylic or polycarbonate, or painted acrylic or polycarbonate provided with the desired preferential light scattering characteristics may be used as well for other applications.

The second component of the present invention is a housing14positioned adjacent the surface15of the waveguide12. Housing14comprises a pair of side walls20,22abutting and downwardly extending from the surface14and defining an open ended channel18that extends substantially the length of waveguide12. The housing14generally functions to house the light source and electrical accessories and to collect light not emitted directly into surface15and redirect it to the waveguide In other words, the housing further serves to increase the light collection efficiency by directing by reflection the light incident upon the internal surfaces of the housing into the waveguide12and assist in the scattering of the light. From a viewer's perspective, it is desirable that the visual appearance of the housing14not be obtrusive with respect to the glowing surface13of the waveguide12; thus, it is preferred that the outside surface of the housing be light absorbing and thus visually dark to an observer. Again, it is preferred that the housing also be made from an impact resistant acrylic material with the outer walls20and22having an outer regions formed from a dark pigmented, thus light absorbing, acrylic while the inner regions are made from a white pigmented, thus light reflecting, acrylic. The two regions are best viewed inFIG. 3Ashow an enlarged segment of wall20in which the outer region20ais the dark acrylic and the inner region20bis the white acrylic. Such acrylic materials preferably are the same as used for the waveguide. While the waveguide12and housing14may be separately formed and then appropriately joined, it is preferred that the components be molded or extruded as a unit in long sections with the channel18already formed.

An alternate wall structure is shown inFIG. 3Bin which the wall20′ has three components, an outer dark region20c, and intermediate light reflecting20d, and a transparent wall20ewhich may be comprised of a scattering acrylic like the waveguide. The outer and intermediate regions20cand20dcould be dark and white coatings painted on the wall20′ which itself may be comprised of a transparent acrylic material or scattering acrylic. The light reflecting coatings can be of a color matching the color of the LED if desired.

Although the above discussion sets forth a preferred construction of the housing, it should be understood that in some applications the reflecting and absorption characteristics may be provided by light reflecting and absorption paint or tape. Additionally, where there is little concern about the visibility of the housing, it may not be necessary to provide the light reflecting and/or absorption characteristics to the outer surface of the side walls.

One the most beneficial attributes of the present invention is the ease that the illumination device10can be bent to form designs or lettering. The channel18permits the device10can easily be deformed and bent into the desired shape. Once the device10has been shaped, the LEDs24and the electrical connection board26are then inserted into the channel18and then the channel18be filled with a filler compound. Thereafter the filler or potting compound is permitted to harden, thus maintaining the positioning of the LEDs and circuit board26. There are various configurations of the LEDs24and board26that may be positioned within the channel18. Examples of the configurations are shown inFIGS. 5A and 5B. A preferred configuration is that shown inFIG. 5because of the compact nature of the arrangement. In this arrangement, it is important, however, to observe the orientation of the circuit board26within channel18so that the board26extends along the length of channel to facilitate bending. The flexibility of the circuit board26with attached LEDs24permit this post design insertion into the channel18with the apex of the LED24essentially abutting the lower surface of the waveguide12(as illustrated in FIG.3). It is also important that the potting compound30used to fill channel18have the desired light transmitting characteristics and be effective in maintaining the positioning of both the LEDs and the board. The potting compound further serves to eliminate air gaps between the LEDs and the waveguide. It is preferable that the potting compound harden into an impact resistant material having an index of refraction essentially matching that of the housing24aof the LEDs24to minimize Fresnel losses at the interface there between. The potting compound further adds strength to the structure by filling in the channel18and assists in reducing hot spots from forming on the lateral surface13. Such potting compounds may be selected from commonly available clear varieties such as, for example, that obtainable from the Loctite Corporation, Rocky Hill, Conn. under the brand name Durabond E-00CL. As is also seen inFIG. 3, the bottom surface of the device10may be covered with a light reflecting surface32which may be, for example, a white potting compound or paint and this optionally covered with a light absorbing material34. In those instances where the selected LEDs24have a certain color the light reflecting surface may also be selected to have a matching or substantially the same color. To take advantage of ambient light certain dyes may be added to the acrylic material so that the device10exhibits some readily distinguishable coloring upon viewing.

The intensity of the point light sources preferably used by the present invention are typically sufficient to provide the requisite brightness. It bears repeating that the quintessentially feature of the present invention, however, is the careful spreading or distribution of the individual light patterns of the point light sources such that the light patterns are preferentially expanded along the light emitting surface and form an oblong or oval-like light intensity pattern. Equally important is that the minor axis of the oval-like light intensity pattern extends substantially the entire circumferential width of the curved light emitting surface. The preferential spreading of each of the light intensity patterns along the waveguide also permits an the overlapping of the individual light patterns. This in turn enables the present invention to provide an observed uniform collective light pattern along and over the entire light emitting surface.

There are various parameters that have an impact on both the brightness and uniformity of the light intensity pattern emitted by the surface13of the waveguide12. Among the most important are the scattering characteristics of the waveguide material, the spacing “l” between LEDs24as shown inFIG. 2, the lensing effect of the LED housing and internal optics where the light emitting portion of the LED resides, the shape and structure of the housing, and the distance “d” (shown inFIG. 3) from the apex of the LED housing24ato the apex point12aon the lateral surface13. To promote uniformity of the light intensity distribution pattern on the surface of the waveguide is that the line of LEDs24must be positioned a predetermined distance “d” from apex point12aof the waveguide. Positioning the LEDs24too close to the surface will cause a “hot spot”, i.e., a region of higher light intensity to locally appear on the surface12aof the waveguide and spoil the quality of the uniform glow. Placing in too far from surface12awill clearly and undesirably diminish the overall light intensity emanating from the waveguide12and may also prevent the minor axis of the oblong or elliptical-like pattern from extending over the circumferential width of the light emitting surface. As an example only, it has been determined that when the curved surface has a radius of curvature of about 3/16 (about 4.76 mm), the device10(shown inFIG. 3) has a height “h” of about 31 mm and a width “w” of about 9.5 mm, and the LEDs have a candle power of about 280 mcd and are spaced apart about 12 mm, the distance “d” should be about 17.75 to 17.80 mm. It should be understood, however, that while the above describes a preferred waveguide structure that resembles neon tubing dimensionally, other and different shapes of waveguides may be used yet still providing the desired uniform glow.

To better understand the principal under which the present invention operates, reference is now made toFIGS. 7A-7Fas examples of the changes of the light intensity and spread of the light pattern comparing light intensity and spread of a typical diode to that of an illuminating device constructed in accordance with the present invention. A single LED or point light source provides a narrow light intensity pattern54as graphically portrayed by FIG.7A. Such a graph can be generated by using a photocell type of device50portrayed in FIG.7B and progressively measuring the light intensity at various angles from the center line51. This light pattern54should be contrasted to the one inFIG. 7Cin which the pattern56is considerably broader with a concomitant reduction in the intensity along the center line51.FIG. 7Crepresents the broad pattern emitted by the lateral surface13of the waveguide12constructed in accordance with the present invention. As stated above, it is important that the distance “d” and the LED spaced apart distance “l” be such that the oval-like intensity patterns of the individual LEDs overlap as portrayed in the schematic representation of FIG.7E and the projection depicted inFIG. 7Cschematically represents a plurality of LEDs24providing an broadened overlapping elliptical-like light intensity patterns31on the lateral surface13of the waveguide12.FIG. 7Eis top view using a Mercator-like projection of the light pattern areas24on the lateral surface.13. The minor axis of the light intensity patterns31are represented by dashed lines33. As stated above, for any given dimension of the waveguide and spacing of the point light sources, it is important that the distance “d” be appropriately set so distance so that the minor axis of the light intensity distribution pattern extends substantially the entire circumferential width of the curved lateral light emitting surface13. For purposes of this disclosure the light intensity distribution pattern can be defined as the visible area of the light pattern extending out from the center region of the area that is visible discernible by an observer.

To further assist in the preferential diffusion and scattering of the light intensity pattern, applicant has further determined that the use of oval shaped LEDs as shown inFIG. 6are helpful. The best effect is obtained when the oval shaped LEDs are positioned so that the major axis of the elliptically shaped light patterns seen in top elevation view is directed along the long axis of the waveguide12. The characteristic light pattern of an oval LED is shown inFIG. 8depicting graphically normalized light intensity along the major and minor axis. As can be seen, the oval LED tends to direct light along its major axis illustrated by the curve36.

The light weight and ruggedness of the illumination device10of the present invention lends itself to ready mounting to almost any surface and by a variety of mounting techniques. For example, as illustrated inFIG. 12, an extended length of the device10could be mounted in curtain rod fashion to a wall board44through the use of a bracket hook40and fastener42. Moreover, successive lengths of the device10can be easily juxtaposed such as, for example, depicted inFIG. 13where dowels46of matching refractive indices with the material of the waveguides12,12′ are inserted in complimentary openings in the respective ends. Other fastening techniques may be employed including gluing of the various lengths together at the ends thereof. In some instances where the lengths when appropriately supported, the ends of the lengths may merely be placed in a juxtaposed touching position. Thus, as can easily be understood, illumination devices10of an indeterminate length can easily be installed and supported.

FIGS. 9A,9B, and9C represent in schematic form but a few of the alternate constructions in which the LEDs24are appropriately spaced from the apex point of the waveguide.FIG. 9Adepicts a light scattering spacer member48between the waveguide12and the LED24. Such spacer48could be fabricated from the same material as the waveguide12, e.g., a high impact resistant acrylic material.FIG. 9Brepresents a construction in which the channel18is dimensioned so that the LED abuts an inner face of the channel and defines a space50between the apex of the LED housing and the waveguide12.FIG. 3shows the use of a transparent potting compound that fills the space between the LED24and waveguide12. The compound could easily be introduced into the channel18after the LED24and circuit board26are placed therein.

FIGS. 10A and 10Billustrate that the configuration of the illumination device10including the waveguide and/or housing could be changed as determined by the application to which the illumination device may be applied.FIG. 10Adepicts parallel side walls20,22that merge into sharply diverging side walls23,25of the waveguide12whileFIG. 10Billustrated as structure in which the walls20,22diverge gradually and blend into the diverging side walls23,25of the waveguide12.FIG. 11depicts further variations to the illumination device10where multiple strings of LEDs may be used in place of the single one discussed above. The various other elements including the reflective and absorption layers are not shown to maintain clarity.

Although it is preferred that the LEDs24be oriented in an upright position as depicted inFIG. 3in order to provide the most efficient light intensity along the light pattern, other positioning arrangements-may be used. One example is shown inFIG. 14where the positioning of the LEDs is tilted so that central axis50′ of the LEDs is placed at some predetermined angle X to the normal orientation50of the central LED axis to the longitudinal axis52.FIG. 15shows the LED24positioned with the apex positioned downwardly (vertically positioned or tilted) with respect to the axial length of the waveguide. The light collection of the various reflective surfaces direct the light from the LED24to the waveguide for the scattering in the same manner as described above.

FIG. 16depicts still another structure where the housing110of the LED120or point light source is incorporated directly in the body of the waveguide100with reflective and absorption layers not shown to maintain clarity.

Technology is being developed where a light source may be fabricated in elongated or rope form from, for example, sheets of electro-luminescencing material that has sufficient light intensity to be juxtaposed to a leaky waveguide in place of the strings of LEDs.FIG. 17illustrates that such a construction of an illumination device140showing an elongated light source170extending in a parallel relationship with the longitudinal axis of the waveguide150within the housing160.

The thin and flexible circuit board26can be obtained from various sources such, as, for example, Flexible Circuit Technologies, Saint Paul Minn. The nature of the electrical connection and the circuitry on the board26depend upon the illumination sequence desired. While the circuitry is not part of the invention, it should be observed that the considerable sequence variety is permitted by the nature of the structure of the present invention. That is, the light weight, resistance to the rigors of packaging, handling, shipping, and installation, and the minimal heating aspects of the illumination device permit essentially endless possibilities for lighting and color sequences. The circuit board, may for example, be provided with various electrical components that permit flashing or fading of the light sources in timed sequences and give the effect of movement Various light source colors can be used and flashed/faded in almost any combination. If the LEDs are interlaced with different colors, then a striping effect can be obtained.FIG. 18illustrates schematically a circuit which may be used with the present invention. A multiplicity of LEDs230are shown connected in series to a remote power source232and to a NPN transistor234in turned connected to a programmable controller236. The LEDs230may be of the same color or in color groupings as desired. A second set of LEDs240(and additional sets of LEDs) similarly connected to the power source232, NPN transistor242, and controller236may be separately grouped or alternated with LEDs230as desired. Using the former grouping, the controller236could be programmed to cause the transistors to go on or off, thus causing the first group and then succeeding groups of LEDs to pulse or flash, simulating motion. Should each of the groups mounted in a device form a sequence of words, for example, “drink cola”, the words could be flashed in sequence. If the LEDs of various groups were alternated in position, the resulting grouping could form a multi-color striping pattern.

From the discussion above, it may now be appreciated that the illumination device of the present invention is rugged and resists breakage that normally would be expected for neon lighting counterparts in shipping and handling. The illumination sources, preferably solid state lighting devices such as LEDs, uses far less electrical energy and remains relative cool to the touch. This allows the illumination device of the present invention to be used in places where the heat generated by neon lighting precludes its use. Moreover, the light weight of the illumination device facilitates mounting on support structures that could not support the relative heavy weight of neon lighting, and its required accessories including the high voltage infrastructure. Finally, the illumination device is flexible in its use, allowing a tremendous variety of lighting techniques very difficult to obtain in neon lighting without substantial expense. Other advantages and uses of the present invention will be clearly obvious to those skilled in the art upon a reading of the disclosure herein and are intended to be covered by the scope of the claims set forth below.