|Publication number||US2689917 A|
|Publication date||Sep 21, 1954|
|Filing date||Dec 28, 1949|
|Priority date||Dec 28, 1949|
|Publication number||US 2689917 A, US 2689917A, US-A-2689917, US2689917 A, US2689917A|
|Inventors||Joseph L Switzer|
|Original Assignee||Joseph L Switzer|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Referenced by (20), Classifications (14)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Sept. 2l, 1954 J. l.. swlTzER FLuoREscENzr DISPLAY DEVICE 2 Sheets-Sheet l Filed Dec.l 28, 1949 ,.1 .Q ..1 ,iii lllllllllllllllllllllllllllllllllllll l v n l.
ATTO NEYS J. L. SWITZER FLURESCENT DISPLAY DEVICE sept. 21, 1954 2 Sheets-Sheet 2 Filed Dec. 28, 1949 INVENTOR Josn/I L-Swfzer BY ATTgZl-fs Hb M y Patented Sept. 21, 1954 UNITED STATES PATENT OFFICE FLUORESCENT DISPLAY DEVICE Joseph L. Switzer, Cleveland Heights, Ohio Application December 28, 1949, Serial No. 135,388
(Cl. Vo-71) 14 Claims.
This invention relates to fluorescent display devices or signs in which the symbols or other indicia comprise fluorescent materials and more particularly to such signs which are illuminated by a source of iluorescigenous radiations disposed at the edge of the display or sign.
Fluorescent displays and signs are highly desirable since they give greater brilliance of colors, greater color contrasts and more pleasing effects than conventional, non-fluorescent signs which selectively absorb and reiiect different wavelengths of incident visible light.
Previous eiforts to provide inexpensive, eiiicient and simple fluorescent signs have failed either because the devices are too complicated and expensive -due to the need for a large source of iiuorescigenous radiations or because the ultimate elfect of the displays are not unlike the usual non-fluorescent signs.
It is generally desirable to direct the light beam onto a sign at as small an angle of incidence as conveniently possible to obtain the greatest amount of illumination, whether the sign is made of non-fluorescent or fluorescent materials. In the latter case, of course, a source of iluorescige- Vnous radiations is used. All commercial sources k of this type normally emit both visible light and ,black lightf or ultraviolet light. When a fluorescent sign is illuminated with both types of light, much of the visible light will be reflected in the usual manner not only from the fluorescent materials on the sign but also from the nonfluorescent materials which are generally used for background portionsV of the sign. This results in a low contrast ratio between the different portions of the sign thus destroying a major part of the effectiveness of the fluorescent sign.
On the yother hand when only ultraviolet light is to be used for illumination, the source of radiations must be provided with lters for blocking out the visible light. These filters however, also block out as much as 50% of the desired ultraviolet radiations. Thus, to obtain the requisite amount of illumination, a much larger source of radiations is needed, which obviously increases installation and operating expense of the display device. Furthermore, since as small an angle of incidence as possible is required for normal Viewing of the sign, it will be seen that large overhanging structures are necessary for proper positioning of the larger sourceof radiations and larger lters with respect to the display.
Another disadvantage of iiuorescent signs in which the radiations are directed toward the sign at as small an angle of incidence as possible is that some of the ultraviolet radiations are refiected to the eye of an observer. These reflected ultraviolet radiations cause the eye, which is susceptible to them to fluoresce to such an extent that the appearance of the sign is foggy and hazy.
Display devices and signs according to the present invention overcome these various disadvantages and provide displays in which the contrast ratios are of a high order and which can be brilliantly illuminated by small commercial sources of fluorescigenous radiation without the need for ltering out the visible radiations.
it is an object of the present invention to provide an edge-lighted iiuorescent sign which utilizes both ultraviolet light and visible light while at the same time obtaining a high contrast ratio and great brilliance.
According to the present invention symbols or other indicia made of a fluorescent composition or material are disposed in optical contact with the rear surface of a transparent panel. A small but efficient commercial source of radiations having wave lengths from about 35100 to about 4500 is disposed at one edge of the panel so that the radiations will pass longitudinally through the panel while being internally reflected at the surfaces thereof. An example of a source of radiations which has been found to be very efficient and effective in the present invention is a fiuorescent tube known as the type 360 BL tube manufactured by the General Electric Company. This tube produces radiations in the violet-blue portion of the visible spectrum and also near ultraviolet radiations, i. e., near the visible portion of the spectrum. The radiations emitted by this tube have wave-lengths varying from about 350D to about Li500 a great proportion of the radiations being in the ultraviolet range and having a wave length of 3650 This tube is not equipped with lters for eliminating the visible radiations.
All of the radiations pass through the panel and strike the fluorescent indicia which is in optical contact with a surface of the panel and are converted to those wave-lengths in the visible .spectrum which are characteristic of the particular fluorescent material upon which the light impmges.
The fluorescent materials which may be employed in the present invention are compounds which are known as daylight iiuorescent compounds. These compounds project visible light of a predominant wave band or color when excited by visible and invisible radiations of a shorter wave length than the predominant wave band.
These colors are very bright due to the fact that they selectively reilect a substantial proportion of the dominant wave band which is present in the incident visible light and, in iiuorescent response to the shorter wave lengths of incident light, emit light of substantially the same wave band as is selectively reflected. The sum of the reflected and emitted light in the predominant Wave band constitutes .the projected light, which may be greater than the `total amount of light `of the dominant wave band which is present inthe incident light. Thus, such compounds may project as much as 120 to 130% of the red light which is present in incident white light. Heretofore, dyes or 'pigments which reflected as much as 60% of the red light in the incident white light were 'regarded as extremely brilliant red materials. Such ycompounds are described in application No. 575,364, iiled January 30, 1945, by Joseph L. Switzer and Robert C. Switzer.
Perhaps one `of the greatest advantages to be derived from the present display device is vthe fact that there lcan be no Yreilected or `emitted light whatever fromithe area surrounding the indicia. These areas, of course, lare free from all kinds of material, ine., they are constituted'solely by the clear uncoated 'transparent panel so that all the radiations are-internally reected within the panel in these rarcas thus rendering the socalled background areas completely light-free and thus invisible to an observer.
The present invention, therefore, provides `a sign or display in whichthe indicia has the lgreatest possible contrast `with the background areas and in which the indicia has a brilliant appearance, composed essentially of pure colors. The effect is comparable to theefect obtained when bright sunlight shines idirectly vthrough stained vglass windows.
If desired the `indicia may be composed of a l single iiuorescen't material so that Va monochromatic sign is obtained. This might be suitable when lettering and Vwords are to be displayed. However, by using a variety of different iluorescent materials anydesired object or scene can be provided in `brilliant colors. Practically any shade of color can be provided by mixing different materials. vSigns or displays of this type are exceedingly lifelike and vpossess a warmth and depth of color not obtained in other kinds of signs. f
The iiuorescent 'materials may be coated directly onto the rear surfaceof the transparent panel'in'the desired pattern or they'canbeapplied to a ilexible sheetof vfabric or paper or the like located behind the panel. In the latter'case the fluorescent materials may be aiixed to the lsheet in patterns and these patterns placed in optical contact vwith the panel or the materials maybe affixed to a substantial area of the sheet and the pattern lformed-by placing-only Yportions of the coated area in optical contact with the panel. In any event only those portions of thev sheet disposed in optical contact with the surface of the panel willbe illuminated. The remaining portions of the sheet, which are not in optical contact with the panel, whether coated-with uores- 4cent material or not will not be Ailluminated by the radiations transmitted through thepanel as described above. They would, of course, be illuminated by extraneous'visible'light which might `st'rike'the front ofthe panel at a 'small angle of incidence.
The invention will-now be'describedin greater detail with reference to the accompanying drawings, in which,
Figure 1 is a front view of a display device according to the present invention, with a portion broken away to show the source of illumination,
Figure 2 is an enlarged vertical cross-section of the device taken along lines 2-2 of Figure 1,
Figure 3 is an enlarged front elevation of a portion of the device with cover removed to show source of illumination,
Figure 41is an kenlarged cross-section of a portion of the panel showing fluorescent material applied thereto,
Figure 5 is a rear elevation of a modied form 'of the device, partly broken away to show various details,
Figure 6 is an venlarged cross-section of a part of the device, taken 'along the line 6-6 of Figure 5,
Figure 7 is an enlarged cross-section of a portion of the panel taken along line 'l-'i of Fig- 'ure.5,
Figure 8 iis `an enlarged cross-section of `a spor- `tion of a modified panel for use in Athe display device.
Acording vto the ln'xodiiication lshown in Figures l to vLl, inclusive, the display device comprises -apanel -l of glass, transparerrtplastic material or lotherzclea'r transparent rmaterial :capable of 'transmitting radiations within the range of vrfrom about 3.500 f. l'to Yabout '4500 A design or other indicia f2 is provided "on the back -of the panel l I asdescribed'rriore 'fully hereinafter. `A light source i3 emitting fluorescigenous radiations, as, for example, Lthe type 3'60 vBlftube previously mentioned, is located near thelower edge of the panel H vwithin a 'housing llt having a removable cover `I 5 as shown in Figure 2.
The panel `Il is provided ywith an yopaque backing member I6 which-'shields the `panel l! from extraneous 'light 'coming from behind -the device. A U-shaped frame 11 "holds the pan-el H and backing member I5 'securely Vtogether 'to form a panelunit'thus protecting v'theindicia-on the rear surfaceof the panel il. The frame -l'fl'extends 'across the top of `the panel and down the sides to a point near the bottom `edge of `the panel il. This frame `in -additionto securing the panel unit ytogether also prevents the escape of -visible'ilig'ht from thesides'a'nd top of the panel.
The housing Ilincludes fa bottom lportion It and a top "I9 v-vvhich is provided with ya vlongitudinally extending hanged vslot 2U adapted to receive the lower vedge `of the panel and backing member vvH5 as shown. Aresi-lient packing 'Z is provided between the panel `unit and the vflanges of the slot 26 to precludethe escape of light 'except through'the pan-l H. l:Space-:i stopl members E22 are secured to the `underside of the v"top le of lhousing lll beneath the slot 2i] vto limit the distance the panelunit'can 7be inserted into the slot. lThe tube I3 islocatedcentrallybeneath the bottom edge of panel 'I'I and'fis secured in place by Vconventional soeketsS 'a-tthe endsof the'housing Ill.
rlhet'op ofthe panelunit-is -held in place `by a bracket 2# r`provided with a channel adapted Vto receivethe top-of'fthelirame VI. The bracket 24, and the'housing IM #may :be secured, as lshown, yby any conventional 'means to a support, such asa wall'25 or the like.
The conventional l.electrical .equipment for fluorescent ytubes'su'c'htasthe electrical -ballast 25 and cable "21 -are ydisposed within kthe housing as shown.
The radiations from the ftubel3 which enter the bottom edge of panel IIpass throughthe panel, being internally reflected from the surfaces of the panel, until they strike the indicia I2 provided on the rear surface of the panel as optical contact with the panel, i. e., so there is no lm of air therebetween. It is highly desirable to also apply a layer 29 of Whitek material suchL as white paint on the layer 28. This extra layer` improves the luminescence of the display by refleeting lvisible light which is emitted by the fluorescent material. It will be clear that both layers 28 and 29 must be in the form of the indicia. The backing member I6 generally consists of a dark material or is coated with a layer 39 of dark colored material, such as flat black paint or the like, which reflects as little light as possible, so that extraneous visible light accidentally falling upon the display device willnot reduce the contrast with the indicia. Since the dark layer 30 is not in optical contact with the panel I I, there being at least a film of vair therebetween, the passage of the radiations Within the panel II will not, of course, be interrupted as when they strike the fluorescent layer 28 which is in optical contact with the panel.
The modification shown in Figures 5 to 7 `inclusive differs from the first modification only in the manner in which the indicia are' disposed in optical contact with the panel I I. The other elements of the device including the source 0f radiations I3 and associated elements are the same as in Figures l, 2 and 3.
In this modification, however, the indicia are not applied directly and permanently to thepanel I I but rather are applied to a flexible sheet which is removably aixed to the panel II. Referring specifically to Figure '7 a flexible sheet 3Ic`om posed of paper` or fabric or the like is provided with a base layer 32 of reflective material such as white paint inthe form of the desired pattern. A layer 33 of fluorescent material, also in the form of the pattern, is superimposed on the reflective layer 32 and then a layer -34 of a pressureadhesive substance, such as the so-called rubber cement, is applied on the fluorescent layer 33. The uncoated portions ofthe sheet 3I are preferably of a dark-non-reflective color.
This sheet can be afxed to the back of the panel II simply by applying pressure so that the indicia will adhere to the panel. Since no lm of air is between the surface of the panel and the fluorescent layer 33, said layer is in optical contact with the panel and will function asin the previously described modification. To more securely x the sheet to the panel a band pf adhesive material may be applied all around the edges of the panel.
One great advantage of this type of arrangement is that the sheet may be quickly and easily removed and another sheet having different indicia substituted therefor. y
)This modification also enables one to provide a sign or display which can be seen from both sides. For example, if a transparent sheet or film is used in place of fabric or paper 3| and if the reflective layer 32 is omitted, the visible light emitted by the fluorescent material will be projected not only through the panel I I, as shown inthe drawings, but also rearwardly through the transparent sheet, thus making the indicia visible from the back also.
A third modification of the present invention;l
is shown in Figure 8. Here the sheet 3I is provided with layers of reflective material 35, nuorescent material 36 and adhesive material 31 over substantial areas of the sheet, and not merely at the location of the desired indicia. In order to obtain optical contact at the desired points so as to produce the desired display, the sheet is pressed onto the panel at those points where luminescence is desired to form the pattern or sign. This arrangement has the advantage that the display may be changed merely by stripping the sheet from the panel and applying pressure a second time at those areas which constitute the new indicia. This system is, of coures, most suitable where substantially monochromatic displays are preferred. When colored pictures or scenes are` desired the type of indicia described in connection with Figures 4 and 7 are required.
In each of the above modifications, the panel I I through which the radiations are transmitted by internal reflection to the fluorescent material, is preferably formed of a solid, hard, clear material capable of transmitting radiations having wave-lengths lying within the range extending from about 3500 through the major proportion, and preferably through the entire visible light spectrum. The panel may be made of glass or a hard synthetic polymeric or plastic material. Most common glasses have satisfactory radiation transmission characteristics as well as certain organic polymers such as polymethyl methacrylate, cellulose acetate, polystyrene, other vinyl polymers, etc.
The 'fluorescent materials `which may be ernployed in the present invention may be of various kinds. In general,l they comprise a carrier ma.- terial having dispersed therein or thereon one or more substances capable of uorescing and emitting visible light when exposed to radiations having wave-lengths lying between 3500 and 4500 Those fluorescent materials which are disclosed in application Serial No. 455,610, filed August-21, 1942, by Joseph L. Switzer, Robert C. Switzer, and Richard A. Ward, U. S. Patent No. 2,417,384, of Robert C. Switzer, and application Serial No. 575,364, filed January 30, 1945, by Joseph L. Switzer and Robert C. Switzer, are particularly satisfactory. These applications disclose fluorescent materials which comprise carriers having dispersed therein organic compounds which iluoresce brightly in daylight. Such materials also emit brilliant visible light when exposed to radiations of wave-lengths lying in the range extending from about 3500 up to about 4500 and hence are excellently adapted to use in the present invention.
The following organic dye compounds may be employed. The fluorescent color for each ccmpound is also indicated.
Meta diethylaminophenol phthalein hydrochloride Red Meta diethylaminophenol succein hydrochloride Red Meta m o n e t h y l aminophenol phthalein hydrochloride Orange The ethyl ester of meta monobutylaminophenol phthalein Orange Meta aminophenol phthalein hydrochloride Yellow green Di (para` dimethylaminophenyl) ketone imine hydrochloride Yellow green 2,3, diphenyl 'N-phenyl quinox- Y alonium sulphate Green p,p Di Ep (p aminobenZoylamino) benzoylaminol stilbene.
o, o di [sodium sulphonatel--. Blue Meta m o n oY-ethylamino'phenol pl'itl1a1ein l Orange Meta m o n o ethylaminophenol phthaleinV ethylester hydrochloride Orange Diamino stilbene di sulphonicY acid (sodium-salt) Blue-White 2, amino, 9(4 aminophenyl) acridonium nitrate Yellow-green 4, amino 1,8 naphthal p-xenylimide Yellow-green 2, [4 amino 8 carboxynaphthyl (l) benzimidazole sodium sulfonate Green Di (dimethylaminophenyl) phenyl amino naphthyl methene chloride Green 4 methyl,l 7 hydroxy coumarin i sodium salt Blue' Such compounds maybe dispersed or dissolved in suitable carrier materials. which` are highly transparent to radiations of Wave-lengths lying between about which have indices of refraction similar to those of glass or synthetic resins used as the panel material. Such carrier materials may becertain soluble or thermoset organic polymeric materials, noncrystallized saccharides and noncrystallized polyhydric alcohols. Examples of suitable soluble polymeric` 'materials useful as carriers are polymeri'zed methyl, ethyl, and butyl methacrylates, polystyrene, polyvinyl ace'- tate, cellulose acetate, ethyl cellulose, and similar compounds. polymeric compounds are polymerized melamine formaldehydev resins, polymerized urea form.- aldehyde resins particularly alcohol-modified urea formaldehyde resins containing no plasticizers, and similar compounds;
glucose and sorbitol.
As set forth in applicationv Serial No. 455,610, the fluorescent material constitutes a solidified carrier material having dispersed therein atleast one such fluorescent organic'compound in a con'- entration of not more than iiv'e perl cent for blueemitting 'compounds to not more than oneV per cent for red-emitting compounds. Particularly good results are obtained when one uses a maximum concentration of from .025 gram for compounds emitting yellow-green light and .015 gram for compounds emitting red light, per cubic centimeter of carrier material; the thickness of the layer of nuorescent material being such that the weight of the iiuorescent compound per square centimeter of surface does not exceed .0005 gram for `each spectral Wave band of light emitted.
Fluorescent compositions may be applied in the form of coatings. If the carrier is a soluble compound, the material may be mixed in suitable proportions with a suitable volatile solvent to form a liquid coating material which may be applied by painting, printing, or screening processes. Evaporation of thesolvent leaves a solid layer ofl fluorescent material.
If the carrier is a thermoset plastic material, partially polymerized carrier material, or the reactants necessary to produce the polymer, and
35Go and about 4500 andv Examples of suitable'thermose't Examples of suitable saccharides and polyhydric alcohols are thev fluorescent compound in proper concentration, are incorporated in a suitable liquid which is applied'to the surface. The resulting coating is baked to remove any volatile liquids present and to form a layer of iiuorescent composition containing the fluorescent compound dispersed in a thermoset polymer.
The fluorescent compound may be incorporated in sheets of organic material, such as fabric or paper sheets or the like instead of being dispersed in carriers. Such fluorescent sheets may be of the type described in U. S. Patent No. 2,417,384, of Robert C. Switzer. Such dyed sheet materials are particularly well suited for use as the flexible sheet illustrated in Fig; 8'.
Inorganic fluorescent pigments may be employed instead 4of organic fluorescent compounds. Examples of suitable inorganic Apigments are the activated alkaline metal sulphides. These pigments may be dispersed in a liquid carrier and applied tothe desired base in the manner indicated above.
Ihe carrier material for the fluorescent dye or pigment may be such that it is tacky and will have adhesive properties. AV flexible sheet having one vor more-areas-coated with such fluorescent material may ybe employed inthe devices described in connection with Fig. 5 to Fig. 8.
However, it is moreadvantageous to employ a separate layer of' permanently tacky, pressure adhesive material over the fluorescent material, as described 'above' withrelation 'to Figs. 5-8.
The elongated body through which the radiations are transmitted by internal reflection may have other forms than'that of a rectangular panel shown in the illustrated embodiments. For example, the 'panel' may be V-shaped in verticalcros's `s'ecti'onwiththeradiations passing into the 'thickrendof 'the Vpanel and being internally reflected from the convergingsurfaces until the angles of 'incidence become less 'than the 'critical angle 'of reflection'. The radiationswill then pass through 'a'surfa'ce' 'of andout of vthepanel in a relatively Wide area. The fluorescent material maybe disposed inoptic'al Contact with the surface'of the panel, either in the area where the radiations p'asfs'through the surface, or in the area Where' there is normally internal reflection of the radiations.' By -this means, a greater intensityofradiation and fluorescence may 'be obtained at points'remote from 'the source of radiation than can bebbtained `with panels having parallel sides Vor 'an'added pleasing effect can be obtained inthe form of 'a' glowor haze at the top ofthe 'display at an area substantially removed from the source of radiations.
While 'the fluorescent material has been disclosed 'as beingcoated'on'a surface of the panel or disposedon a flexible'sheet adjacent the panel, the fluorescent material may also be disposed in recesses or channels formed ina vsurface of the panel 'to provideunusual eifects when irradiated.
The present' invention' thus provides display devices whichv Aov'eic'o'm'e' the shortcomings of prior devices illuminated by fluorescigenous radiation, and make possible for the rst time a compact, inexpensive,l efficient display device in which the patterns are formed of fluorescent materials irradiated by iluorescigenous radiation to emit brilliant, glowing visible light of many colors.
Various modifications may be made in the devices described above without departing from the spirit of the present invention. The scope 9 of the present invention is defined by the appended claims.
What is claimed is:
1. A fluorescent display device comprising a transparent panel capable of transmitting fluorescigenous radiations and having opposed continuous surfaces, a source of unltered fluorescigenous radiations disposed adjacent the edge of said panel so that said unfiltered radiations may be transmitted without interruption through the panel by internal reflection from the surfaces thereof, and fluorescent material in optical contact With selected areas of one of said opposed continuous surfaces of the panel whereby visible radiations are emitted from said material when excited by the fluorescigenous radiations and a substantial portion of said emitted visible radiations pass without internal reflection through the areas of the opposed surface opposite said selected areas to which the uorescent material is in optical contact.
2. A device as claimed in claim 1 wherein the fiuorescigenous radiations from said source include radiations having wave lengths within the range of from about 3500 to 4500 3. A device as claimed in vclaim 1 wherein the fluorescent material is applied directly to the surface of the panel.
4. A device as claimed in claim 1 and further comprising a light reflective material superimposed on the uorescent material in optical contact with said panel.
5. A device as claimed in claim 4 and further comprising a backing sheet of dark color disposed behind said panel and said fluorescent material and light reiiective material.
6. A device as claimed in claim 1 wherein said panel is composed of glass.
7. A device as claimed in claim 1 wherein said panel is composed of a clear, transparent plastic material.
8. A device as claimed in claim 1 wherein the fluorescent material is responsive to daylight.
9. A uorescent display device comprising a transparent panel capable of transmitting fluorescigenous radiations and having opposed continuous surfaces, a source of uorescigenous radiations disposed adjacent the edge of said panel, so that said radiations may be transmitted without interruption through the panel by internal reflection from the surfaces thereof, a flexible sheet of dark color disposed behind said panel, iiuorescent material aliixed to said sheet and facing said panel, a pressure adhesive material superimposed on said fluorescent material for adhesion to said panel at selected areas so that said fluorescent material will be in optical contact with said panel at said selected areas, whereby visible radiations are emitted from said material when excited by the fluorescigenous radiations.
10. A device as claimed in claim 9 wherein said uorescent material is affixed to said sheet only at said selected areas.
11. A device as claimed in claim 9 further comprising a light reflective material disposed between said fluorescent material and said flexible sheet.
12. A device as claimed in claim 11 wherein the light reiiective material, the fluorescent material and the adhesive material are aiiixed to the exible sheet and are superimposed on each other in the order named only at said selected areas.
13. A device as claimed in claim 9 wherein the iiuorescent material and the adhesive material substantially cover said flexible sheet and wherein said adhesive material is adhered to said panel only at selected areas.
14. A device as claimed in claim 9 wherein the fluorescent material is responsive to daylight.
References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,813,491 Gillard July 7, 1931 1,850,319 Fensom et al. Mar. 22, 1932 2,097,625 Langlotz Nov. 2, 1937 2,223,409 Dixon Dec. 3, 1940 2,247,409 Roper July 1, 1941 2,358,203 Best Sept. 12, 1944 2,358,867 Madan Sept. 26, 1944 2,417,384 `Switzer Mar. 11, 1947 2,548,126 Sholkin Apr. 10, 1951 FOREIGN PATENTS Number Country Date 401,151 Great Britain Nov. 9, 1933 402,825 Great Britain Dec. 11, 1933 OTHER REFERENCES Black Light Applied to Plastic Signs, Modern Plastics, pp. 144, 145, April 1946.
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|U.S. Classification||250/462.1, 40/543, 250/458.1|
|International Classification||G09F13/18, C09K11/02, F21V8/00, G09F13/20|
|Cooperative Classification||G09F13/20, C09K11/025, G02B6/0081, G09F2013/1868|
|European Classification||C09K11/02B, G02B6/00L6U, G09F13/20|