USRE20640E - Luminous display ok reflector sign - Google Patents

Description

Jan. 25, 1938. J. c. STIMSON 20,640

LUMINOUS DISPLAY OR REFLECTOR SIGN 7 Original Filed July 9, 1923 5 Sheets-Sheet 1 I mam LUMINOUS DISPLAY OR REFLECTOR SIGN Original F'iied July 9 1923 5 Sheets-fiheet 2 y W f/Z 34 a, H

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Jan. 25, 1938; J, c, s l so Re. 20,640

LUMINOUS DISPLAY OR REFLECTOR SIGN Original Fil ed July 9, 1925 s Sheets-Sheet 5 Reissued Jan. 25, 1938 R 20,640

UNITED STATES PATENT OFFICE 20,640 I LUMINOUS DISPLAY R REFLECTOR SIGN Jonathan C. Stimson, Chicago, Ill.

Original No. 1,809,761, dated June 9, 1931, Serial No. 650,403, July 9, 1923. Reissue No. 18,166, dated August 25, 1931, Serial No. 544,649, June 15, 1931. This application for reissue Decemher 2, 1937, Serial No. 177,837

21 Claims. (01. 40-130) This invention relates to luminous displays,- tance. Such signs are, moreover, very expensive and more particularly to luminous display or reg to install and operate. flector signs. In luminous display signs in which the sign In the accompanying drawings: area is painted or formed to provide display 3 Figures 1 and 2 are a side elevation and a plan characters which are illuminated by directing view respectively showing an illustrative lumilight from a suitable source or sources onto the nous display or reflector sign embodying this in Sign area, the characters are visible by diffuse vention. reflection. Such reflection fills the entire hem- Figure 3 is a plan showing another embodiisphere in front of the sign although serving a ment of this invention; useful purpose within only a small zone. By 10 Figures 4 and 5 are views illustrating the prinreason of the nature of the surface of such a ciples of operation of a reflector used in the lusign a large part of the light is absorbed, even minous display sign embodying this invention; when the sign is painted with ordinary paint. Figure 6 is a perspective view of a prismatic In order to avoid high lights, flat paints are plate used in the display sign; sometimes used resulting in a matte surface.

Figures '7. 8 and 9 show different applications From such a surface the light is even more fully of the reflector or prismatic plate in the formadiffused and there is a greater absorption of tion of display characters on the luminous dislight. As a result the sign, in proportion to the play or reflector sign embodying this invention; amount of illumination used is effectively vis g Figures 10, 11 and 12 are enlargements of porible at short distances only. Further, even at my tions of Figures 7, 8, and 9 respectively, showing short distances such signs lack the brilliance of the reflecting units forming the outline of the electric si character. One of the objects of this invention, therefore, Display signs as heretofore d are of t is to provide means of creating luminous display 2.3 general types, namely: those in which the light reflector Signs in Which the light directed 26 is radiated from lamps forming the display charthe Sign area and more particularly on the acters of the sign,'and those in which the'chary characters. is so em 0r reflected as to asters are displayed by diffu e refle ti from be confined within a selected field from which the surfaces of the character on the sign area. the display characters are Visible; this 15 30 Where the light is radiated directly fro the complished in the illustrated embodiments of this 30 lamps fo -min the Characters, only a small part invention by reflecting the light from the disoi the total emitted light is useful; for only a play characters m the form Spreading small percentage of the total emitted light from cimcentmted beam or beams Into that Selected a bulb or a, series of bulbs is utilized for display vlslble field purposes, keeping in mind that the light from Anoffher i of thls invent!!! 15 topmvldei a bulb is radiated in a sphere of which the source lummous dlsplay reflector havmg forms the center and that the useful light for play characters i wlthm fi display purposes forms only a small sector of the field the hghtdemltted fmrln t e 1 arsphere. Accordingly since the intensity of the acters 1S sqcqncentrate f qon-tm led as o be illumination varies inversely as the square of the confined wlthm that thls 1S accomplished distance it necessafly follows that in Order to 0th in the illustrated embodnnents of this invention tain a practical range of visibility bulbs of relby providing the characters with reflecting atively high candle power must b used faces which are so constructed and arranged as Not is dis 1a m 1 m f to reflect the light impinging thereon from a 1.3 mt slgn p Oymg s or variety of angles, in the form of a spreading but Y m F m energy the concentrated beam or beams and into that semaintenance cost in the replac ln n of bulbs lected. visible field; all in order to display the a r pmr n r ly 5 l s especially characters within that field and render the dissmce in order to secure a display of given charplay 1egib1e and, visibie at great djstances I); act ers, these characters must be built up y Further objects will appear from the detail Semis of l h r q irin a m l plic ty of ul description taken in connection with the accom- Moreover such characters being built up by panying drawings, v spaced p n s ur es of light an only approxi- Generally stated and in accordance with this mate the outline of the character, and require invention the luminous display or reflecting sign high power lamps to make them visible at a dishas a sign character or characters provided with or formed of reflecting units arranged to form the outline or outlines of the character or characters. Each of these units comprises an optical system and has a reflecting area adapted to reflect light incident thereon from a distant source back. in the general direction of the light source, irrespective, within limits, of the angle of incidence of the light. The units have means or are constructed to slightly spread the reflected light; that is, the light reflected from the units is so concentrated and controlled as to confine the reflected light within the desired field and to exclude it from outside spaces, in order to render the character or legend legible at great distances. In accordance with this invention the useful light reflected is so controlled as to be concentrated within an included angle of twenty degrees. The reflecting units are usually arranged along the strokes of the character the impinging light to outline the same. These units may be arranged in clusters along the character.

In accordance with an illustrative embodiment of this invention the reflecting surfaces forming the characters of the luminous display or reflector sign are in the form of triple reflectors constructed as shown and described in Patent No. 1,671,086, issued May 22, 1928.

A central triple reflector comprises three reflecting surfaces arranged to intersect at a common point and such a reflector has the property of reflecting incident beams back to their source irrespective (within limits) of the angle of incidence of such a beam with respect to the axis. Where the triple reflector is a prism causing reflection of the incident beam, the limiting angle of incidence (with respect to the axis) can be increased while the loss of reflected rays 1s dc:- crease-d for any given angle of incidence. How

ever, in an optically accurate central triple reflector (in which the reflecting surfaces are at right angles to each other so as to form in effect the corner of a cube and which is provided with optically plane surfaces) the incident beams are reflected directly back to the source. Such a reflector will, therefore, merely produce a "halo whose annular width at the source is equal to the diameter unit will be observable only when the eye of the observer is halo. A reflector of that character, therefore, has no practical utility in a luminous display or reflecting character sign. In the sign embodying this invention the reflected light is spread to reach the eye of an observer located a substantial distance outside of a line connecting the reflecting unit or units with the light source, but the spread is so concentrated and controlled (within an included angle of twenty'degrees) as to secure the desired distance legibility and visibility.

The triple reflector described and shown in the patent referred to is so constructed as to reflect in the form of a concen spreading beam or beams. in an embodiment of the the patent referred to, by

trated and controlled This is accomplished invention described in deviating the reflecting surfaces thereof slightly from true right angular relation and by distorting the surfaces, so as to vary from the true optical surface of a central reflector; specifically stated this latter is accomplished in a prismatic reflector by forming the reflector of pressed glass and by so controlling the degree of polish of the reflecting surfaces as to leave the same suflicienta ly rough and undulating to secure spread reof the reflecting unit, so that the close to the source and within the shown undulating (on an exaggerated scale) so that an incident beam I 3 from a source of light I 4 provided with a reflector l5 tsuch as a parabolic reflector) is reflected in the form of a spreading beam which is of uniform intensity, the spread of the beam being controlled by the degree of polish given the reflecting surfaces.

As a practical illustrative embodiment a reflecting area is formed by a prismatic plate l1 of pressed glass, which has formed on the back thereof a series of triple reflecting prisms [8 arranged in contiguous relation, the reflecting sunfaces of these prisms being formed by pressing in a suitable mold and the polish of the reflecting surfaces being controlled by the degree of polish given the mold surfaces. Such a prismatic plate has the property of reflecting incident substantially parallel beams of light back past the source in the form of a cone having the plate as the which the transparent total triple reflecting prisms function being signs.- If service conditions require an angular range and quantity of reflection beyond the refleeting range of the transparent prismatic plate, the back or figured face of the plate may be silvered, thus widening the range through which all of the units of the reflector will function.

In the procedure described in Patent 1,671,086 directions are given which will produce units of pressed glass in which the useful reflected light while spread as required, will be so controlled as to be concentrated within. an included angle of twenty degrees.

The mold, or matrix of the reflector is constructed with the angles approximately accurate, that is, within about one degree of ninety degrees (90), but not within a second or less as is required in an optical device if a defined undistorted image (halo) is to be secured. The surfaces of the mold are made as plane as is conveniently possible and are given a degree of polish. If not polished too highly there are minute irregularities in the surfaces that result in a symmetrical spreading of the light as it is successively reflected upon the three surfaces; the irregularities forming a large number of minute reflecting surfaces of different angles, these surfaces varying sufliciently from a true plane to cooperate together in the multiple reflection of the three surfaces so as to spread the light to a degree, but not varying sufficiently from ninety degrees (90) to scatter-the light out of a defined beam or field.

In practice a reflector suitable for most purposes is secured by giving the mold the highest possible polish, the grain of the metal and the effect of shrinkage of the glass in the pressing operation providing a surface, the reflection from which has about the proper amount of spread. As will, however, be obvious the spread of the beam and the uniformity thereof can be controlled by the degree of polish. Where the greatest ieasible distance legibility and visibility is required and the observer is located at a point fairly close-to the line connecting the reflector with the source of light, then it is necessary to suflicient for most display make the mold for the pressed glass reflector 7 carefully,

with a sufficiently high degree of accuracy and polish upon the surfaces so that the reflected'beam will be confined to a cone with a small angular spread.

In the case of hollow type reflectors of the character described formed by silvered mirrors set at approximately right angles, the surfaces of the silvered glass or other reflecting surfaces can be slightly broken up or left partially unpolished so as to vary from a true plane sulhciently to secure a spreading beam and uniform distribution of the light. This can readily be secured in the case of silvered surfaces of glass by using ordinary window glass for the reflectors, or as a cover glass for the front of the reflector. Where the reflector is made of pressed glass so as to form a transparent solid or prismatic reflector, the front face is in that case conformed to a surface of the mold so as to form a face which deviates from aplane. In these embodiments, therefore, employing silvered window glass for the reflectors, a cover of window glass, or prismatic glass plates formed to shape as described, there is placed in front of the reflecting surfaces, a heterogeneous or irregular refracting medium which will operate to secure a definite spreading beam and uniform distribution of the light.

Each of the units is, therefore, constructed to direct a definite but concentrated spreading beam of substantially uniform intensity into the selected field. Furthermore by the employment of a prismatic construction as shown in Figure 6, in which a series of comparatively small units are arranged in contiguous relation, there will be a composite beam made up from the beams of the several units and they work together to make a more or less rather uniform field, even if the angles in the several units vary from ninety degrees but within the limits described. The several units in such a case cooperate to cause a blending of the beams from the several units. By grouping these reflectors in contiguous relation over the reflecting face, varying orientations of the unit reflectors with respect to any given beam is secured. In view of the fact that the reflector units are arranged in contiguous relation, with each unit constructed as heretofore described, the spreading fields of light from the several units merge into a definite spreading beam. The composite beam from the several reflecting units is, therefore, confined within the selected field.

The application of the reflecting prism to luminous display or reflector signs can be varied to suit requirements. Thus as shown in Figures '7 and 10, the characters l9 may be formed of pressed glass having formed on the back there-' of a series of triple reflecting prisms whose vreflecting surfaces are formed as heretofore described. These characters may either be used integrally or may be built up of parts, and such characters, or the parts thereof may be secured r to a sign area in any suitable manner, it being understood, of course, that these prisms will project from the rear part of the character.

As shown in Figures 8 and 11, and 9 and 12 the sign area 20 or 2| may be formed of a prismatic plate, either in a single piece or built up from a series of plates. with the reflecting surfaces formed as heretofore described and with of the the triple reflecting prisms on the back sign area. The characters 22 or 23 may then be formed either by coating the sign area, leaving the outlines of the characters exposed as shown in Figures 8 and 11 or by coating the characters leaving the back-ground exposed as shown in Figin the first case, Figures 8 and 11, the characters will appear illuminated while in the second case Figure 9, the background will appear illuminated. It will be understood, of course, that any suitable opaque paint or other ures 9 and 12;

coating may be used and this coating mayeven be translucent and in varying colors so as to present a varied color display. It will, of course, be understood that the total sign area need not be formed as a reflecting surface in either case but only such portions as are required. With this form of sign area the display characters may be varied by removal of the coating and by the application of a new coating.

Figures 1 and 2 show the application of this invention to a location. The frame of the sign i is provided ed in any manner as heretofore described while the light is directed on the sign area and the display characters thereon from a suitable source,

such as one or more lamp bulbs and a reflector 25 which is arranged to project the light on the sign area and the display characters. Any suitable reflector of a highconcentrating type, such as a parabolic reflector or a recently developed compensating Mangan mirror 'may be provided. Such a spot-light is so constructed and arranged as to throw a spreading beam in order to just cover the sign area and the display characters thereon. From the principles of the reflector as heretofore described, it will be readily seen that the light will be reflected from the display characters in the form of a spreading but concentrated beam or beams and into the selected field (which is, in this case, along the street or thoroughfare 4), which field is that from which the luminous display is visible. It will be understood, of course, that the source of light and impinging reflector 25 and the sign area are so relatively positioned and with respect to the visible field, (with the light source in front of and distant from the sign and located in the field) and that the spread of the beam is controlled as heretofore described, as to confine the reflected light within the visible field. Accordingly maximum efficiency and maximum' legibility, visibility and brilliance will be obtained with a minimum of current consumption. will of course. be understood that a lamp of sufficiently high candle power and a reflector ofa sufficient size will be small relative to the sign area so that the sign area and the characters thereon will not be obscured by the presence of the source within the reflected beam; as a practical proposition the light projecting reflector 25 will really be invisible at a comparatively short distance from the sign area.

Occasionally a sign is favorably located in a position where it may be viewed without obstruction over a large territory. Such a location may be secured on the top of an open public square or at the intersection of wide avenues forming an acute angle. Such a location is shown in Figure 3 where the frame of the sign I containing the sign area 24 constructed as heretofore described is located on top of a building 26. In order to secure a distributed field, but still retain a concentrated spreading beam, two or more spot-lights 21 and 28 are located to face the sign area, as by mounting the same on buildings 29 and 39 respectively. spot-light 2.1 can be arranged so as to direct a beam 3i on the sign area, which beam will be reflected in the form of a concentrated spreading beam 32, while the beam 33 from the spot-light 28 with a sign area 24, which is construct-t a high building facing.

is reflected in the form of a concentrated spreading beam 34. The elements may be so constructed and relatively arranged as heretofore described, that the light will be reflected from the display characters in the form'of concentrated spreading beams into the selected visible field, the light from the display characters and incident from the several sources being reflected into selected adjacent visible field areas so as to confine the light reflected from the sign area and the display characters thereon within the visible field.

By thus suitably arranging a series of spot-lights imum efliciency is secured even with the losses incident to the employment of reflectors and refractors. Not only is the cost of installation low, but the maintenance cost is low for the reason that the sign area is rugged and will not deteriorate. Nor will the efliciency be impaired on account of the exposure to weather for the reason that the reflecting surfaces are in the rear where they can be protected. Where silvered plates are employed the reflectors may be sealed to the sign board or similarly treated so as to protect them from the weather. If transparent total reflecting plates are used little protection is necessary. It is to be noted in this connection that dust particies, if not in optical contact with the reflecting surfaces, will not impair the reflection but optical I contact can readily be avoided by protecting the back against rain. The'display sign is so constructed that any suitable characters in the form of letters, figures, illustrations and trade-marks may be employed without resorting to block characters. Moreover any suitable color effect may be obtained as heretofore described by suitable coating applied to the sign area. A desired color effect may also be secured by introducing a color screen in the path of the beam from the spot-light or by passing a varied color screen therethrough. Elaborate flashing effects may also be secured by simply moving an opaque 'screen in the path of the beam from the spotlight, or by moving one containing perforations designed to secure the desired efl'ect, or by using a semi-transparent screen containing gradations of shading. Furthermore the sign area may be converted and changed readily as heretofore described without great expense.

It will thus be seen that in accordance with this invention there is produced a character sign by which the characters of such a sign are delineated to an observer at great distances by reflection of light directed thereon and that the sign embodying this invention has the following characteristics, namely:-a sign area in a location where it has a narrow useful field of visibility; a distant light source located within the visible field; and a reflecting area comprising a multiplicity of reflecting units arranged to delineate the character of the sign. These reflecting units, however, have the following characteristics, namely:of directing light back towards a distant light source regardless of the particular position of any unit on the sign area and regardless of the particular position of the light source with respect to the reflecting area; of distributing that reflected light in a narrow spreading beam, generally confined within the selected narrow visible field of the sign but substantially uniform throughout the field of spread; these reflecting units combining to create a desired leg end in the eye of the observer by directing light from such parts of the area as delineate the character of the legend to each point in the narrow selected field of visibility.

While a number of embodiments of this invention have been described and illustrated in an illustrative environment, it will be understood that this invention is susceptible of various embodiments and in various environments in the general art of reflecting signs to perform their useful functions in those environments. It is further obvious that various changes may be made in details without departing from the spirit of this invention; it is, therefore, to be understood that this invention is not to be limited to the specific details shown and described.

The expression reflecting area as used in some of the claims comprises the summation of the reflecting areas of the reflecting units as they appear on the sign delineating the character or characters. The statements in the specification and claims to the effect that the reflected light or the useful reflected light will be concentrated within an included angle of twenty degrees, have reference to an angle or cone, with the unit or units from which the reflected beam or beams emanate as the apex of the angle or cone. This, of course, will be the useful angle or cone defining the field in which the sign will be visible to the eye of an observer at great distances (hundreds of feet) and which represents the concentration of the light within the return beam or cone as distinguished from any fringe of such low intensity that it can be disregarded.

Having thus described the invention, what is claimed is:

1. A luminous display sign comprising, a re fleeting area on which characters are displayed so as to be visible in front of said area, and alight source in front of but distant from said area and located in a selected field, adapted to direct the light on said area for reflection within the selected field, said reflecting area being composed of reflecting surfaces of an optical system formed and positioned to reflect the light to the selected field, irrespective, within limits, of the angle of incidence of the light, and further constructed to cause a definite spread of the reflected light from said area, but concentrated within an included, angle of twenty degrees and so as to confine the reflection within the selected field, in order that the characters may be visible to an observer anywhere within that field.

2. A luminous display sign comprising, a reflecting area on which characters are displayed so as to be visible in front of said area, and a light source in front of but distant from said area and locatedin a selected field, adapted todirect the light on saidarea for reflection within within limits, of the angle of incidence of the light, each of said units being further constructed to cause a definite spread of the reflected light therefrom, but concentrated within, an included angle of twenty degrees and so as to confine the reflection within the selected fleld, in order that the characters may be visible to an observer anywhere within that field.

3. A luminous display sign comprising, a reflecting area on which characters are displayed so as to be visible in front of said area, and a light source in front of but distant from said area and located in a selected field, adapted to direct the light on said area for reflection within the selected field, said reflecting area being composed of a series of reflecting units arranged in contiguo-us relation, each of said units comprising an optical system constructed and positioned to reflect the light to the selected field, irrespective, within limits, of the angle of incidence of the light, each of said units being further constructed to direct a definite spreading beam of substantial uniform intensity, but concentrated within an included angle of twenty degrees, into the selected field, and the composite beam from the several reflecting units being confined within the selected field, in order that the characters may be visible to an observer anywhere within that field.

4. A luminous display sign comprising, a reflecting area on which characters are displayed so as to be visible in front of said area, and a light source in front of but distant from said area and located in a selected field, adapted to direct the light on said area for reflection within the selected field, said reflecting area being composed of a series of reflecting units arranged-in contiguous relation, each of said units comprising an optical system having reflecting surfaces constructed to direct a definite spreading beam into the selected field, irrespective, within limits, of the angle of incidence of the light, each of said units having means for distributing the reflected light uniformly throughout the field of spread, but concentrate the light within an included angle of twenty degrees, and the composite beam from the several reflecting units being confined within the selected field, in order that the characters may be visible to an observer anywhere within that field.

5. A luminous display sign comprising, a reflecting area on which characters are displayed so as to be visible in front of said area, and a series of light sources in front of but distant from said area and located within selected, adjacent fields, adapted to direct the light from said area for reflection within the selected adjacent fields, said reflecting area being composed of reflecting surfaces of an optical system formed and positioned to reflect the light to the selected field.

irrespective, within limits, of the angle of incidence of the light and further constructed to cause a definite spread of the reflected light from said area, but concentrated within an included angle of twenty degrees and so as to confine the reflection within the selected fields, in order that the characters may be visible to an observer anywhere within those fields.

6. A luminous display sign having display characters visible from within a selected field, and a light source in front of and distant from said characters, said characters having reflecting surfaces of an optical system arranged in relative angular relation tomultiply reflect light impinging thereon and back towards the light source in the form of a spreading beam or beams, but concentrated within an included angle of twenty degrees, said reflecting means being adapted to direct the reflected light into and confine the same to said field in order to display said characters within said field.

T. A luminous display sign having display characters visible from within a selected field, and a light source in front of and distant from said characters, said characters being formed by total reflecting prisms whose surfaces are arranged in angular relation to multiply reflect the light in the form of spreading beams, but concentrated within an included angle of twenty degrees into and confined within the selected field.

8. A luminous display sign having display characters visible from Within a selected field, and a light source in front of and distant from said characters, said characters being formed by triple reflecting surfaces which deviate from their true right angular relation adapted to reflect light in the form of spreading beams, but concentrated within an included angle of twenty degrees, into and within the selected field.

9. A luminous display sign having display characters visible from within a selected field, and a light source in front of and distant from said characters, said characters being formed by triple reflecting surfaces adapted to reflect light impinging thereon back towards the light source, and means cooperating with said surfaces adapted to slightly spread the reflected light to a definite degree in the form of a spreading beam or beams, but concentrated. within an included angle of twenty degrees so as to confine the same within said field.

10. A luminous display sign having display characters visible from within a selected field, and means in front of and distant from said characters for directing light indiscriminately on said characters, said characters" having triple reflectors whose reflecting surfaces deviate from their true right angular relation adapted to reflect the light impinging thereon in the form of spreading beams, but concentrated within an in cluded angle of, twenty degrees so as to confine the same within said field.

11. A luminous display' sign having display characters visible from within a selected field, and means in front of and distant from said characters for directing light from a source on the display characters, said characters being reflecting surfaces arranged in relative angular relation to multiply reflect the light impinging on said display characters back towards said source, and means cooperating with said surfaces adapted to slighly spread the reflected light to a definite degree in the form of a spreading beam or beams, but concentrated within an included angle of twenty degrees so as to confine the same within said field.

12. A reflecting sign having a sign character provided with reflecting units arranged to form an outline of the character, each of said units comprising an optical system having a reflecting area and adapted to reflect light incident thereon from a distant source back in the general direction of the light source, irrespective, within limits, of the angle of incidence of the light, each of said units having means adapted to slightly spread the reflected light but concentrate the light within an included angle of twenty degrees.

13. A reflecting sign having a sign character provided with reflecting units arranged along the strokes of the character, each of said units comprising an optical system having a reflecting area adapted to reflect light incident thereon from a distant source back in the general direction of the light source, irrespective, within limits, of the angle of incidence of the light, each of said units having means adapted to slightly spread the reflected light but concentrate the light within an included angle of twenty degrees.

14. A reflecting sign having a sign character provided with clusters of reflecting units arranged to form an outline of the characten each of said units comprising an optical system having a reflecting area adapted to reflect light incident thereon from a distant sourceback in the general direction of the light source, irrespective, within limits, of the angle of incidence of the light, each of said units having means adapted to slightly spread the reflected light but concentrate the I light within an included angle of twenty degrees.

15. A reflecting sign having a sign character provided with clusters of reflecting -units arranged to form an outline of the character, each cluster being composed of a series of units arranged in contiguous relation, each of said units comprising an optical system having a reflecting area adapted to reflect light incident thereon from a distant source back in the general direction of the light source, irrespective, within limits, of the angle of incidence of the light, each of said units having means adapted to slightly spread the reflected light but concentrate the light within an included angle of twenty degrees.

'16. In a reflecting sign, the combination with a reflecting area consisting of a number of prisms, whose opposite sides meet at substantially right angles at their apices. and which are adapted to reflect light incident thereon from a distant source back in the general direction of the light source and which have means adapted to slightly spread the reflected light, but. concentrate the light with,- in an included .angle of twenty degrees, of means for blocking out portions of the reflecting area to form a design;

17. In a reflecting sign, a single plate of glass having onone side a reflecting area consisting of a number of prisms, whose opposite sides meet at substantially right angles at their apices and which are adapted to reflect light incident thereon from a distant source back in the general direction of the light source and which have means adapted to slightly spread the reflected light, but concentrate the light within an in- 1 cluded angle of twenty degrees, said plate havtrate the light within an included angle of twenty degrees, of means for blocking out portions 0 the area to form a design.

19. In a reflecting sign, the combination with a reflecting area consisting of a sheet of plate glass on which are formed a number of prisms whose opposite sides meet at substantially right angle at their apices and'which are adapted to reflect light incident thereon from a distant source back in the general direction of the light source and which have means adapted to slightly 5 spread the reflected light, but concentrate the light within an included angle of twenty degrees, of means for blocking out portions of the reflecting area to form a design.

20. In a reflecting sign, the combination with a reflecting area consisting of a sheet of plate glass on which are formed a number of substantially right angled tetrahedra, said tetrahedra adapted to reflect light incident thereon from a distant source back in the general direction of the light source and having means adapted to slightly spread the reflected light, but concentrate the light within an included angle of twenty degrees, of means for blocking out pontions of the reflecting area to form a design.

21. In a reflecting sign, a plate of glass having on one side thereof a plurality of tetrahedral prisms, said prisms adapted to reflect light incident thereon from a distant source back in the general direction of the light source and having me.-ns adapted to slightly spread the reflected light, but concentrate the light within an included angle of twenty degrees, said plate having on its other side an opaque coating disposed to block out a sign substantially as and for the purpose described.

JONATHAN C. STIMSON.

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