WO1989002638A1

WO1989002638A1 - Improved traffic control head

Info

Publication number: WO1989002638A1
Application number: PCT/US1988/003067
Authority: WO
Inventors: Tom Lawson; David H. Thakar; Michael N. Thakar
Original assignee: Taliq Corporation
Priority date: 1987-09-11
Filing date: 1988-09-12
Publication date: 1989-03-23

Abstract

An indicator for presenting a visible image in a traffic control environment. The indicator may comprise a message bearing member and an electrically operable optical shutter means (132, 133) for alternately blocking and transmitting light. The shutter means is positioned between the message bearing member and a viewing area in front of the indicator. The indicator may further include a neutral density film (131) positioned between the optical shutter means and the viewing area. The message bearing member may have a translucent message portion (134, 135) and a substantially opaque mask (136) may be positioned adjacent to a major surface of the message bearing member wherein the mask has a substantially transparent portion in registration with the message portion. The shutter means can have a first operative state in which it optically transmits incident light and a second operative state in which it optically scatters incident light so that light transmitted through the substantially transparent portion of the mask and the translucent message portion passes through the optical shutter means in the first state and is scattered by the optical shutter means in the second state.

Description

IMPROVED TRAFFIC CONTROL HEAD

BACKGROUND OF THE INVENTION

This invention relates to traffic control heads of the type used to provide visible control or advisory messages to pedestrians or motorists.

Traffic control heads are widely used to provide a variety of messages to motorists. Examples of such traffic control heads are highway intersection traffic signal lights which provide red, amber and green control messages to both motorists and pedestrians, pedestrian signal heads, which provide WALK/DON'T WALK control messages to pedestrians, and amber cautionary flasher units used to advise passers-by of dangerous conditions requiring increased alertness. All such traffic control heads share in common a message indicator, i.e., the colored lenses of the intersection controller, the pedestrian and outstretched palm colored symbols or WALK/DON'T WALK written message of the pedestrian control head, or the amber lens of the cautionary marker; a light source for back lighting the message indicator; a housing; a power source; and a means of switching and/or flashing.

The object of a traffic control head is to alert individuals regarding the control or advisory messages, relying on the visual senses to convey the information. The message indicator and light source function in combination to achieve this object: the message indicator by making available the control or advisory information message, and the state of the light source signifying that the message is operative or inoperative.

The requirement that traffic control heads be capable of functioning effectively throughout the day and during nighttime creates two contrasting functional criteria. During daytime, the illuminated message indicator must be clearly discernible over a wide range of ambient light intensity conditions ranging from relatively low ambient light intensity in the presence of relatively dark overcast conditions to relatively high ambient light intensity during bright sunlight. At night, the ambient intensity is normally somewhat more stable, varying in accordance with changes in the artificial illumination (e.g., street lights, business signs and vehicular head lamp activity) .

During daylight, strong sunlight shining directly on the different colored lenses of an intersection signal head or on the message indicator portions of a pedestrian control head can mask entirely the effect of the light source thereby rendering the state of the traffic control head indistinguishable to viewers. Such bright light may in fact produce a false signal where the inoperative portion of the message appears operative. This effect is known as "sun phantoming" and obviously can produce dangerous situations.

One attempted solution to this problem has been to employ a relatively high intensity light source in a traffic control head. This attempted solution, however, has met with mixed results. While the high intensity light source reduces somewhat the masking effect of bright light shining directly on the message indicator, it does not eliminate the masking effect entirely. In addition, a high intensity light source is relatively more expensive than a low intensity source, with respect to both initial cost and operating expense. Moreover, during nighttime, or in dark ambient daylight conditions, a relatively high intensity light source produces an illumination for the message indicator which is uncomfortably intense and causes viewer eye glare. While this secondary problem might be overcome by providing a light intensity adjustment system for the traffic control head in order to tailor the light source intensity to the level of ambient intensity, such a solution is expensive to implement, introducing additional elements which are prone to failure and which increase the operating cost for each traffic control head.

Another attempt to improve the visual performance of traffic control heads, which has been specifically directed toward the direct sunlight illumination masking problem ("sun phantoming") , has been to employ passive light shields arranged between the message indicator and ambient light in order to shield the message indicator from ambient light while still affording sufficient visibility of the message indicator. These shields have taken various forms, such as a visor for a traffic signal head or parallel rows of louvers for pedestrian control heads. While somewhat effective in reducing the masking problem during high sun angle periods, this solution fails during the low sun angle periods when sunlight is parallel with the screen such that the screen fails to cast its shadow on the messageindicator. Moreover, the use of screens reduces the angularity or peripheral visibility of the message indicator to the viewer.

Another attempted solution directed to the problem of light masking has been to employ a specially formed neon tube sign shaped in accordance with a message symbol. While this attempted solution results in some improvement, the basic masking problem still exists. In addition, such neon tube signs are relatively expensive to produce and are fragile.

SUMMARY OF THE INVENTION

The invention comprises a visual message indicator- which is relatively inexpensive to implement, highly reliable in operation and extremely effective over the entire range of ambient lighting conditions from full darkness to full direct sunlight.

The invention, in one embodiment, comprises a message bearing member, an electrically operable shutter means for alternately blocking and transmitting light, and a neutral density film. The optical shutter means is positioned between the message bearing member and a viewing area in front of the indicator. The neutral density film is positioned between the optical shutter means and the viewing area. The invention may be utilized with a pedestrian head signal, a traffic control head, and a programmable signal head.

In another embodiment, the invention comprises a message bearing member having a translucent message portion and a substantially opaque mask positioned adjacent to a first major surface of the message bearing member. The mask is provided with a substantially transparent portion in registration with the message portion of the message bearing member. An electrically operable optical shutter means is positioned adjacent to a second major surface of the message bearing member. The shutter means has a first operative state in which it transmits incident light and a second operative state in which it scatters incident light so that light transmitted through the substantially transparent portion of the mask and the translucent message portion passes through the optical shutter means in the first operative state and is scattered by the optical shutter means in the second operative state. The optical shutter means is preferably fabricated from a liquid crystal material capable of being operated in the two states noted above.

The message indicator may also include a substantially transparent face plate member positioned between the mask and ambient light, the face plate member being preferably fabricated from glass or a suitable plastic material.

The message bearing member, the mask and the one or more optical shutter means may be secured together.

The message indicator is mounted within the forward opening in a housing containing a light source mounted to the rear of the forward opening in such a position that light radiation from the light source illuminates the optical shutter means and is visible through the translucent message portion and, if utilized, the substantially transparent portion of the mask when the light source is energized.

Means may be provided within the housing for absorbing light transmitted from ambient light through the optical shutter means; and a reflector may be located within the housing for concentrating light from the light source on a region of the optical shutter means in registration with the translucent message portion.

In a further alternate embodiment of the invention, at least two visual message indicators are each located in a corresponding forward message indicator region in a housing, and two corresponding light sources are each positioned in the housing between a corresponding one of the message indicator forward regions and a rear portion of the housing. The housing includes means for. impeding the passage of light radiation from a given one of the light source to the other message indicator region to prevent optical interference, the impeding means may comprise a partition positioned between the two forward regions of the housing. Alternatively, the impeding means may comprise an aperture substrate.

The invention provides one or^" more visual messages that may employ a relatively low intensity light source without sacrificing the visual presentation of the desired message or messages. The invention may be designed to be installed in existing traffic control heads, pedestrian control heads and hazard warning indicators.

For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 A perspective view of one embodiment of a pedestrian control head;

Figure 2 A front view of the head of Figure 1 illustrating the WALK message; Figure 3 A front view of the head of Figure 1 illustrating the DON'T WALK message;

Figure 4 An exploded perspective view of the head of Figure 1;

Figure 5 A sectional view taken along lines 5-5 of Figure 1;

Figure 6 An enlarged fragmentary sectional view of a first embodiment of the visual message indicator taken from the line segment 6-6 of Figure 5;

Figure 7 A schematic diagram of a power switching circuit;

Figure 8 A block diagram of an alternate circuit with photosensor- control;

Figure 9 A perspective view of a preferred embodiment of a pedestrian control head;

Figure 10 A schematic side view of the components of the visual message indicator assembly shown in Figure 9;

Figure 11 A schematic diagram of a power switching circuit for the embodiments illustrated in Figures 9-10 and 12-13;

Figure 12 A perspective view of another embodiment of a pedestrian control head;

Figure 13 A schematic side view of the components of the visual message indicator assembly shown in Figure 12. Figure 14 A schematic view of a signal head in accordance with the present invention; and

Figure 15 A schematic view of a programmable signal head in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the drawings, wherein like components - are designated by the same reference numerals, Figure 1 illustrates in perspective view a pedestrian control head incorporating the invention. As seen in this Figure, the head includes a major housing 10, and a forward louvered deflector grill 11. These elements are conventional and form no part of the invention.

With reference to Figures 2 and 3, carried within the pedestrian control head is a visual message indicator described below for providing the WALK and DON'T WALK visual messages illustrated, respectively, in Figures 2 and 3. Specifically, as shown in Figure 2, when the WALK message is displayed, the conventional pedestrian figure is rendered visible to a viewer while the conventional palm figure is not visible. With reference to Figure 3, when the DON'T WALK message is displayed, the conventional palm figure is rendered visible, while the conventional pedestrian figure is rendered non-visible. In some applications, the conventional palm figure is flashed on and off to signify the approach of the end of the walk period, while the conventional pedestrian figure is steadily illuminated.

Figures 4-6 illustrate the opto-mechanical components of an embodiment of the invention. As best seen in Figures 4 and 5, mounted within the inner recess of housing 10 is a lamp/reflector assembly generally designated with reference numeral 15. Assembly 15 includes a pair of low intensity incandescent bulbs 16, 17, typically having a value in the range from about 25 to 40 watts, mounted in a conventional lamp socket 18, which in turn is secured to the rear wall 20 of the assembly 15.

Each bulb 16, 17 is mounted within a separate compartment formed by a vertically arranged partition 28 and aperture plates 25, 26. The aperture is of a given size to allow uniform illumination of the message indicator from the light source radiation while minimizing the visibility of the light bulb compartment. The viewer side of the aperture plates 25, 26 is coated with a black matte finish or other suitable light absorbing material. The light bulb or back side of the aperture plates 25, 26 may be of a reflective material to increase light output from the light source. The vertical partition 28 extends forwardly of aperture plates 25, 26 in order to provide a shield which substantially reduces or completely eliminates cross-illumination from either lamp 16 or 17 to the region forward of the other lamp. The portion of the partition 28 on the bulb side of the aperture plates 25, 26 may be of a reflective material in order to increase light output from the lamps, while the portion of the partition 28 on the viewer side of the aperture plates 25, 26 may be coated with a black matte finish.

The entire sub-assembly consisting of elements 25, 26 and 28 is received within a relatively rigid casing 29 dimensioned to be accommodated within the interior of conventional housing 10.

Arranged forwardly of assembly 15 is a visual message indicator assembly generally designated with reference numeral 30. Assembly 30 comprises a sandwich which includes a transparent front plate 31 which functions as a protective plate for the other elements described below and is preferably fabricated from glass or a suitable plastic, such as a polycarbonate or acrylic material. If desired, the forward face of plate 31 may have a diffuser surface, such as a pebble finish surface. Positioned immediately behind place 31 is an opaque mask 32 having a^■ first palm-shaped cut-out 33 and a second pedestrian-shaped cut-out 34. Mask 32 has a black matte finish to minimize light reflections from the surface thereof. If desired, mast 32 may be silk- screened onto the rear surface of plate 31.

Positioned behind mask 32 are a pair of translucent colored sheets 36, 37 of the standard colors for the DON'T WALK and WALK messages. Specifically, sheet 36 is portland orange, while sheet 37 -is lunar white.

Positioned behind sheets 36, 37 are a pair of optical shutters 40, 41 (shutter 41 being illustrated as removed, for clarity) . ^" Each shutter 40, 41 comprises a relatively thin liquid crystal plastic material sold under the trademark OPTO-film by Taliq Corporation of Mountain View, California. This material is described in detail in U.S. Pat. No. 4,435,047 issued March 6, 1984, the disclosure of which is hereby incorporated by reference. Briefly, this material scatters light when no electric field is applied thereto and becomes transparent when subjected to an electrical field, which may be supplied by a power supply of appropriate voltage, e.g., 60 volts AC. In the light scattering or de- energized state, the material exhibits an effective light scattering property, in both the forward direction ^"(through-scattering) and the reverse direction (back-scattering) . The liquid crystal material is relatively durable and maintains its two-state optical properties even when punctured, and is thus relatively vandal proof.

Electrical connection between each optical shutter 40, 41 and the associated power source may be afforded by means of a pair of electrically conductive strips 42, 43 mounted on opposite edges of the shutter. Conductive strips 42, 43 may comprise copper tape available from 3M Corporation. Shielded conductive wires 44 are suitably connected (e.g., by soldering) to the conductive strips 42, 43.

The embodiment of the assembly thus far described corresponds to the limited structure illustrated in enlarged detail in Figure 6.

The entire assembly 30 may be provided with a peripheral seal 45, typically rubber, and the assembly 30 is retained in place in the forward region of housing 10 by means of the diffuser grill 11 which is pivotably mounted by means of apertured feet 46 to spaced apertured feet 47 formed in the lower outside wall portion of housing 10, using hinge pins 48. At the top forward wall portion, diffuser grill 11 is removably clamped by means of fasteners 49 pivotably attached by means of pins 50 to spaced upper apertured feet 51 formed in the upper forward wall portion of housing 10, and claw-like lugs 52 formed in the upper wall of diffuser grate 11. In the position illustrated in Figure 4 , the diffuser grill is illustrated in the open or hinged position. In the closed position illustrated in section in Figure 5, the forward edge of vertical partition 28 bears against the peripheral seal 45, as illustrated.

Again with reference to Figure 5, the aperture plate 25 (and corresponding aperture plate 26) are recessed rearwardly of the optical shutters 40, 41 in order to prevent bleedthrough of the black aperture surface through the shutters 40, 41 and those portions of cut-outs 33, 34 in registration with the solid portion of aperture plates 25, 26.

Figure 7 illustrates in schematic form a power circuit for energizing lamps 16, 17 and optical shutters 40, 41. As seen in this Figure, an AC power source 60 is coupled by a first switch 61 to a first terminal of lamp 16 and optical shutter 41; and source 60 is further coupled by means of a second switch 62 to a first terminal of lamp 17 and optical shutter 40. The connection from the remaining terminals of lamps 16, 17 and optical shutters 40, 41 are returned to the other side of power source 60. In use, with switch 61 open and switch 62 closed, as illustrated, power is applied to optical shutter 40 (DON'T WALK) and lamp 17 (WALK). Consequently, in this state,_, optical shutter 40 is transparent while

^~_ optical shutter 41 is in the substantially opaque or light scattering state. In this state, shutter 41 scatters light incident on the sheet surface in both the forward and backward directions. Consequently, any light passing through mask cut-out 34 and colored

(transparent) sheet 37 is scattered by the optical shutter 41. Similarly, light from lamp 17 which strikes optical shutter 41 is also scattered. In contrast, any ambient light passing through cut-out

33 and colored sheet 36 passes through optical shutter 40 and is absorbed by aperture plate 25. To a viewer standing in front of the pedestrian control head, the pedestrian WALK sign is rendered visible, while the palm DON'T WALK sign is not visible.

When switch 61 is closed and switch 62 is open, lamp

16 (DON'T WALK) is energized, lamp 17 is de- energized, optical shutter 40 is placed in the scattering state and optical shutter 41 (WALK) is placed in the transparent state. To a viewer, the palm symbol becomes visible while the pedestrian symbol is rendered non-visible. Switches 61, 62 are functionally linked as suggested by the broken line in the simple circuit of Figure 9. It is understood that switches 61, 62 are illustrated as mechanical switches for clarity only. In practice, triac-based electronic switching circuits are preferably employed. Since the design and construction of such circuits are well-known to those skilled in the art, further details are not given herein. For examples of two such circuits which can be modified to provide the switching required for a pedestrian control head, reference should be had to commonly owned, co-pending application Serial No. 856,356, filed April 28, 1986, entitled "Flashing Advisory Sign", the disclosure of which is hereby incorporated by reference.

If desired, in those installations in which ambient light alone is ordinarily sufficient to render the messages visible, when desired, without the need for supplemental illumination provided by lamps 16, 17, a photo detector may be employed to override the normal switching of lamps 16, 17 to limit the application of power to the lamps 16, 17 to low intensity ambient light conditions. As seen in Figure 8, an AC source 64 is coupled to an AC switch control unit 67 containing the necessary logic and triac elements to apply AC voltage to lamps 16, 17 and optical shutters 40, 41. Timing of the switching is schematically illustrated in Figure 8 by a timer unit 65, which may take the form of a discrete timer located at the site of the pedestrian control head, or timing signals generated by a master vehicle control system and transmitted to the pedestrian control head site by means of suitable data communications links. A photo detector 63 measures ambient light and blocks the activation of lamps 16, 17 when the ambient light lies above a predetermined threshold. This function can be implemented using conventional logic circuitry.

Although lamps 16, 17 are illustrated as incandescent lamps, it is understood that other equivalent light sources, such as fluorescent lamps, may be employed. In addition, if desired a reflector indicated with phantom lines 70 in Figure 5 may be provided for lamps 16, 17.

It is further understood that any external wiring required for the electrical operation of the embodiment shown may be routed through either upper aperture 72 or lower aperture 74 formed in housing 10.

Fi.gures 9-10 illustrate the ^"opto-mechanical components of a preferred embodiment of the present invention. The visual message indicator assembly 130 in this embodiment includes, from the viewing region, a sheet of neutral density film 131, a pair of optical shutters 132, 133, translucent colored sheets 134, 135, an opaque mask 136, and a reflector 137.

Neutral density film 131 is preferably fabricated of a translucent material such as a translucent neutral acrylic. The "f" stop of the material is selected to optimize the brightness of the display while controlling the "off" message indicator color to uniform darkness.

The optical shutters 132, 133 are positioned immediately behind the neutral density film 131. Each shutter comprises a thin sheet of Opto-Film. As discussed, the Opto-Film is switchable between an energized (clear) state and a de-energized (light scattering) state. Positioned behind optical shutters 132, 133 are a pair of translucent colored sheets or lenses 134,

135. The colored lenses 134, 135 have the standard colors for the DON'T WALK and WALK messages. Specifically, lens 134 is portland orange, while lens

135 is lunar white. The neutral density film impedes

(absorbs) light transmission without filtering a particular color spectrum. This means that the film does not color the light which would change the specified portland orange and lunar white, e.g.., of the colored sheets 134, 135.

Opaque mask 136 is located behind lenses 134, 135. Mask 136 has the palm-shaped cutout 33' and the pedestrian-shaped cutout 34'. Mask 136 has a finish and color that substantially matches the unilluminated color of the display. Particularly, the masking color is color-coordinated with the color of the accumulation of the colored lenses 134, 135, the optical shutters 132, 133, and the neutral density film 131.

Located behind opaque mask 136 is a reflector 137.

The reflector is used to reflect internal light. The reflector may have appropriate cutouts 33', 34' formed therein.

Mounted within the inner recess of housing 10 is a lamp/reflector assembly 15 like that illustrated in Figures 4-6. As discussed, assembly 15 includes a pair of low intensity incandescent bulbs 16, 17 mounted in a conventional lamp socket which is secured to the rear wall of assembly 15.

A vertically arranged partition 28 provides a shield which substantially reduces or eliminates cross- illumination from either bulb 16 or 17. The bulbs are mounted in separate compartments formed by partition 28 and aperture plates 25, 26. Each lamp may further include a parabolic reflector like that shown in Figure 14 for directing incident light toward an observer of the traffic control head. The entire subassembly 15 is received within a relatively rigid casing 29 dimensioned to be accommodated within the interior of housing 10.

The circuitry.for energizing lamps 16, 17 and optical shutters 132, 133 is schematically illustrated in

Figure 11. It comprises appropriate electrical leads, A.C. power source 60, and switches 140, 142.

In operation, with the switch 140 open and switch 142 closed, as illustrated, power is applied to optical shutter 133 and lamp 17 (WALK) . Consequently, in this state, optical shutter 133 is transparent while optical shutter 132 scatters incident light. As a result, to a viewer- standing in front of the signal, the pedestrian WALK sign is rendered visible, while the palm DON'T WALK is not visible.

When switch 140 is closed and switch 142 is open, lamp 16 (DON'T WALK) is energized, lamp 17 is de- energized, optical shutter 133 is in the light scattering state, and optical shutter 132 (WALK) is in its transparent state. Thus, to a viewer, the palm symbol (DON'T WALK) becomes visible while the pedestrian symbol is not visible.

Switches 140, 142 are functionally linked as suggested by the broken line in the simple circuit of Figure 11. However, it is understood that the switches are illustrated as mechanical switches for clarity only. In practice, electronic switching circuits are preferably employed. Since the design and construction of such circuits are well known to those skilled in the art, further details are not given herein.

Another embodiment of pedestrian head is illustrated in Figures 12-13. The lamp/reflector assembly 15 of this embodiment may be identical in construction to the embodiment illustrated in Figures 9-10, and thus is not described in detail.

The visual message indicator assembly 130' of this embodiment is similar in construction and operation to the visual message indicator assembly 130 described with reference to Figures 9-10. Assembly 130' includes a neutral density film 131, a pair of optical shutters 132, 133., and appropriate colored lenses 134, 135. Additionally, it includes an aperture substrate 170 extending between colored lenses 134, 135 and lamps 16, 17.

Aperture substrate 170 includes first and second shafts or tunnels extending between light sources 16 and 17, and palm-shaped cutout 33'* and pedestrian- shaped cutout 34'', respectively, in substrate 170. The respective shafts may have a conical or tubular cross-section, and are preferably fabricated from a light reflective material. The aperture substrate substantially reduces or completely eliminates cross- -illumination from either lamp 16 or 17 to the region forward of the other lamp.

The circuitry for operating the embodiment illustrated in Figures 12-13 may be similar in arrangement and operation to that shown in Figure 11. Accordingly, it is not described in any detail here.

In the embodiments of Figures 9-10 and 12-13, during the "on" or energized state of the optical shutter, light, in the desired shape, is transmitted to an observer or viewer of the pedestrian head. The light transmission and color contrast in the "on" or energized state to the unillu inated area is very good even in direct sunlight. During the de- energized or "off" state, the unilluminated area will appear the same as the unilluminated mask area under all lighting conditions. Therefore, when the "on" and "off" states are contrasted when in actual operation, the "on" state is easily distinguishable from the "off" state under all lighting conditions.

Figure 14 illustrates a signal or traffic control head 120 constructed in accordance with the principles of the present invention. The traffic control head may, for example, be a flashing warning sign or a stop light including a solid red, green and amber ball. The head comprises a housing 110 and a lamp/reflector assembly generally designated with reference number 115 mounted within the inner recess of housing 110. Assembly 115 includes a low intensity incandescent bulb 116 mounted in a conventional lamp socket 118, which in turn is secured to the rear wall of the housing. The assembly 115 further includes a parabolic reflector 117 for directing incident light toward an observer of the traffic control head.

Traffic control head 120 further includes a sheet of a neutral density film 122 covering the forward opening of housing 110. As discussed, film 122 may be a ' translucent material such as a translucent neutral acrylic. Disposed inwardly of film 122 is an optical shutter 124 of the type described heretofore, namely, an optical shutter comprising a sheet of Opto-Film. Disposed between shutter 124 and bulb 116 is a lens 126. Lens 126 may be a translucent colored sheet having a desired color, for example yellow for a flashing caution indicator or red for a flashing stop indicator.

Optical shutter 124 is switched between the de- energized (light scattering) and energized (transparent) states in conjunction with the off and on operation, respectively, of signal head 120. A simple circuit for accomplishing this is schematically illustrated in Figure 14.

As shown, such as circuit 144 may include an electric power supply 146, such as a battery, and a switch

148. The electric power supply may alternatively be a source of alternating current. This circuit is connected by electrical leads 145, 147 to electrodes that are positioned on opposite sides or surfaces of the liquid crystal material of optical shutter 124.

The electrodes may be ^• substantially optically transparent, and may be formed on optically transparent substrates. For the sake of clarity, neither the electrodes nor the substrates are illustrated in Figure 14.

Operationally, when switch 148 is opened, no electric field is applied to the liquid crystal material of optical shutter 124, which is then in the so-called de-energized or field-off condition or mode in which light is scattered such that the colored sheet or lens is not visible to an observer of the traffic control head. With switch 148 closed, an electric field is applied across the liquid crystal material of optical shutter 124, which then goes into the energized or field-on condition or mode, or non- scattering light state, in which the colored lens 126 is visible.

Figure 15 illustrates a programmable signal head 150 incorporating the concepts of the present invention. As seen in this figure, the programmable signal head includes a colored fresnel lens 152 located at the forward end of chamber 153 of the signal head. The signal head further includes a ground glass diffuser 154, a lamp 156, which may be located in a lamp housing (not illustrated) , and tape masks 158 for the diffuser.

The illuminated diffuser 154 is placed at the focal plane of fresnel lens 152. At this point, each point on the surface of the diffuser will illuminate one and only one angular position in the viewing field of the signal head. If it- is desired to exclude some portion of the viewing field from illumination, the masks 158 are utilized to mask off the corresponding region of the diffuser. The operation and arrangement of such a programmable signal head is described in greater detail in U.S. Patent 3,457,400 issued July 22, 1969, to Roger H. Appeldorn, entitled "Apparatus and Method For Directing a Beacon Toward a Limited Viewing Area", and which disclosure is hereby incorporated by reference.

Under conditions of high level external illumination, enough light will be reflected from the colored fresnel lens 152 to make the signal head appear to be "on" even when lamp 156 is unlit. This "phantoming" effect is eliminated by disposing a OPTO-Film optical shutter 160 and a neutral density film 162 in front of lens 152. The neutral density film, as discussed, is preferably fabricated of a translucent material such as translucent neutral acrylic. The f-stop of the material may be selected to optimize the brightness of the display while controlling the uniform darkness of the message indicator when in the de-energized state. In operation, the optical shutter 160 is in the energized state (transparent) when the signal head is "on", and in the de-energized state (light- scattering) when the signal head is "off". Appropriate circuitry, such as shown in Figure 15, is provided so that the optical shutter 160 may be switched between its de-energized and energized states in conjunction with the "off" and "on" „ operation (lamp 156 unlit or lit) of signal head 150.

This circuitry may simply include a battery 172 and a switch 174 connected by appropriate electrical leads 176, 175 in circuit with optical shutter 160 and lamp 156. When switch 174 is closed, both the lamp and the optical shutter are energized such that the signal head is "on". When switch 174 is open, the lamp and optical shutter are de-energized so that the signal head is "off". As stated heretofore with respect to the above-discussed embodiments, more complex electronic switching circuitry or a different circuit may be provided to operate the signal head in accordance with the principles of the present invention.

As will now be apparent, visible message conveying devices constructed according to the teachings of the invention possess significant advantages over known units. Firstly, unlike conventional units, the image contrast improves with increasing intensity of ambient light, due to the scattering capability of the optical shutters in the inactivated state in combination with the light absorbing characteristics of the covers and inserts. As a consequence, back illumination lamps of substantially lower power can be employed without impairing the visual acuity of the visual messages. In addition, in ambient conditions above a threshold value the message indicators can still function even after lamp failure since the lamps 16, 17 are used to supplement the ambient light in rendering the image visible. Moreover, due to the simplicity of construction, units fabricated according to the invention can be designed as modular replacements to existing units in the field, thus eliminating the need for expensive redesign of the housing and face plates. Further, since relatively low power lamps may be employed during low ambient light conditions, the visual images may be produced during such conditions with little or no glare. In addition, under ambient light conditions above a threshold intensity value, the unit will still operate when a lamp burns out.

While the above provides a full and complete disclosure of the invention, various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the invention. Further, while the type of message illustrated is the combination of color and symbol, other types of visual messages, such as words, symbols alone or colors alone are encompassed with the scope of this disclosure. Therefore, the above description and illustration should not be. construed as limiting the scope of the invention which is defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A visual message indicator comprising: a message bearing member; an electrically operable optical shutter means for alternately blocking and transmitting light positioned between said message bearing member and a viewing area in front of the indicator; and a neutral density film positioned between said optical shutter means and the viewing area.

2. The invention of Claim 1 wherein said message bearing member includes a translucent message portion.

3. The invention of Claim 2 wherein said message bearing member comprises a colored lens.

4. The invention of Claim 1 further including a light source positioned behind said message bearing member.

5. The invention of Claim 4 further including a reflector means positioned behind said message bearing member for reflecting internal light.

6. The invention of Claim 1 further including a housing having a forward opening, and a light source mounted in said housing to the rear of said forward opening and wherein said message bearing member is mounted in said housing between said light source and said optical shutter means.

7. A visual message indicator comprising: a condensing lens defining a viewing surface and having a focus; aperture-defining means for outlining a restricted area corresponding to a viewing area forwardly of the indicator and with all aperture- defining edges substantially at the focus; a light source means for providing diffuse illumination to the condensing lens from the focus and from the entire aperture; an electrically operable shutter means for alternately blocking and transmitting light disposed between the condensing lens and the viewing area; and a neutral density film disposed between said optical shutter means and the viewing area.

8. A visual message indicator comprising: a message bearing member having a translucent message portion; a neutral density film positioned between said message bearing member and a viewing area in front of the indicator; an electrically operable optical shutter means for alternately blocking and transmitting light positioned between said message bearing member and said neutral density film; and a substantially opaque mask positioned on the side of said message bearing member opposite from said electrically operable shutter means, said mask having a substantially transparent portion in registration with said message portion.

9. The invention of Claim 8 further including a reflector means positioned behind said mask for reflecting light.

10. The invention of Claim 9 wherein said message bearing member comprises a colored sheet.

11. The invention of Claim 8 wherein the color of said mask substantially matches the unilluminated color of said message bearing member.

12. The invention of Claim 8 further including a light source positioned behind said mask.

13. The invention of Claim 12 further including a reflector means positioned about said light source for reflecting internal light.

14. The invention of Claims 1, 7 or 8 wherein said sheet of neutral density film is a translucent material.

15. The invention of Claims.4, 7 or 12 further including means for alternately applying electrical power to said optical shutter means and said light source so that said optical shutter means transmits light when said light source is energized and blocks light when said light source is de-energized.

16. The invention of ciaims 1, ^'7 or 8 wherein said optical shutter means includes a liquid crystal means.

17. The invention of Claim 16 wherein said liquid crystal means includes a liquid crystal material and a containment means for inducing a distorted alignment of said liquid crystal material which in response to such alignment at least one of scatters and absorbs light and which in response to an electric field reduces the amount of such scattering and absorption.

18. The invention of Claim 17 wherein said liquid crystal material is birefringent and has an ordinary index of refraction in the presence of an electric field that is substantially matched to the index of refraction of said containment means to minimize refraction and scattering of light and an extraordinary index of refraction in the absence of the electric field that is different from the index of refraction of said containment means to cause refraction and scattering of light.

19. The invention of Claim 16 further including 5 electrode means at the opposite surfaces of said liquid crystal means for applying an electric field across said liquid crystal means.

20. A visual message indicator comprising: a message bearing member having a translucent

10 message portion;^" a substantially opaque mask positioned adjacent a first major surface of said message bearing member, said mask having a substantially transparent portion in registration with said message portion; and

15 an electrically operable optical shutter means positioned adjacent a second major surface of said message bearing member, said shutter means having a first operative state in which the shutter means optically transmits light and a second operative

20 state in which the shutter means optically scatters light so that light transmitted through said substantially transparent portion of said mask and said translucent message portion passes through said optical shutter means in the first operative state

25 and is scattered by said optical shutter means in the second operative state.

21. The invention of Claim 20 further including a sheet of neutral density film positioned between said optical shutter means and ambient light.

30 22. The invention of Claim 21 wherein said sheet of neutral density film is a translucent material.

23. The invention of Claim 20 further including a __ housing having a forward opening, and a light source mounted in said housing to the rear of said forward opening and wherein said message bearing member is mounted in said housing between said light source and said optical shutter means.

24. The invention of Claim 23 further including means for alternately applying electrical power to said optical shutter means and said light source so that said optical shutter means is placed in said first operative state when said light source is energized and in said second operative state when said light source is de-energized.

25. The invention of Claim 24 further including a reflector located between said light source and said mask for reflecting internal light.

26. The invention of Claim 20 wherein the color of said mask substantially matches the unilluminated color of said message bearing member÷

27. The invention of Claim 20 wherein said optical shutter means includes a liquid crystal means.

28. The invention of Claim 27 wherein said liquid crystal means includes a liquid crystal material and a containment means for inducing a distorted alignment of said liquid crystal material which in response to such alignment at least one of scatters and absorbs light and which in response to an electric field reduces the amount of such scattering and absorption.

29. The invention of Claim 28 wherein said liquid crystal material is birefringent and has an ordinary index of refraction in the presence of said electric field that is substantially matched to the index of refraction of said containment means to minimize refraction and scattering of light in an extraordinary index of refraction in the absence of said electric field that is different from the index of refraction of said containment means to cause refraction and scattering of light.

30. The invention of Claim 27 further including electrode means at the opposite surfaces of said liquid crystal means for applying an electric field across said liquid crystal means.

31. The invention of Claim 20 wherein said message indicator further includes a substantially transparent face plate member positioned between said mask and ambient light.

32. The invention of Claim 31 wherein said face plate member is fabricated from a material selected from the group consisting of glass and plastic.

33. The invention of Claim 20 wherein said message bearing member, said mask and said optical shutter means are secured together.

34. The invention of Claim 20 further including a housing having a forward opening, and a light source mounted in said housing to the rear of said forward opening; and wherein said message bearing member is mounted to said housing in the region of said forward opening in a position between said light source and ambient so that light radiation from said light source illuminates said optical shutter means and is visible through said translucent message portion and said substantially transparent portion of said mask.

35. The invention of Claim 34 further including means for alternately applying electrical power to said optical shutter means and said light source so that said optical shutter means is placed in said first operative state when said light source is de- energized and said optical shutter means is placed in said second operative state when said light source is energized.

36. The invention of Claim 34 further including reflector means for concentrating light from said light source on a region of said optical shutter means in registration with said translucent message portion.

37. The invention of Claim 34 further including means within said housing for absorbing light transmitted from ambient through said optical shutter means.

38. A device for presenting a plurality of visible messages comprising: a housing having at least two message indicator forward regions and a rear portion; at least two visual message indicators each located in a corresponding one of said message indicator regions, each said visual message indicator including a message bearing member having a translucent message portion, a substantially opaque mask positioned adjacent a first major surface of said message bearing member, said mask having a substantially transparent portion in registration with said message portion, and an electrically operable optical shutter means positioned adjacent a second major surface of said message bearing member, said shutter means having a first operative state in which the shutter means optically transmits incident light and a second operative state in which the shutter means optically scatters incident light so that light transmitted through said substantially transparent portion of said mask and said translucent message portion passes through said optical shutter means in the first operative state and is scattered by optical shutter means in the second operative state; at least two light sources each mounted in said housing between corresponding ones of said message indicator forward regions and said rear portions; and means for selectively applying electrical power to each of said optical shutter means and said light sources so that light radiation from a given light source illuminates the corresponding one of said optical shutter means and is visible through the corresponding translucent message portion and said substantially transparent portion of the corresponding mask.

39. The invention of Claim 38 further including a substantially transparent face plate member positioned between at least one of said masks and ambient light.

40. The invention of Claim 38 wherein each of said optical shutter means includes a liquid crystal means.

41. The invention of Claim 40 wherein said liquid crystal material means comprises a liquid crystal material and containment means for inducing a distorted alignment of said liquid crystal material which in response to such alignment at least one of scatters and absorbs light and which in response to an electric field reduces the amount of such scattering or absorption.

42. The invention of Claim 38 further including a neutral density film positioned between said optical shutter means and ambient light.

43. The invention of Claim 42 wherein the message bearing member, the mask, the neutral density film, and the optical shutter means of each of said visual message indicators are secured together.

44. The invention of Claim 38 wherein said means for selectively applying electrical power provides that one of said optical shutter means is placed in said first operative state when its corresponding light source is illuminated while the other of said optical shutter means is placed in said second operative state.

45. The invention of Claim 38 wherein said means for selectively applying electrical power provides that one of said optical shutter means is placed in said first operative state when its corresponding light source is. not illuminated while the other of said optical shutter means is placed in said second operative state with its corresponding light source illuminated.

46. The invention of Claim 38 further including reflector means for concentrating light from said light sources on a region of the corresponding optical shutter means in registration with the corresponding translucent message portion.

47. The invention of Claim 46 further including means within said housing for absorbing light transmitted from ambient through said optical shutter means.

48. The invention of Claim 38 wherein said housing further includes means for impeding the passage of light radiation from a given one of said light sources to the message indicator regions corresponding to the other light sources.

49. The invention of Claim 48 wherein said device includes two visual message indicators and two light sources each associated to a different one of two forward regions, and wherein said impeding means comprises a partition between said two forward regions.

50. The invention of Claim 48 wherein said device includes two -visual message indicators and two light sources each associated to a different one of two forward regions, and wherein said impeding means comprises a first shaft extending between a first one of said light sources and one of said two forward regions and a second shaft extending between a second one of said light sources and the other one of said two forward regions.