Multiple colored searchlight signal unit

A searchlight signaling device including a housing in which is mounted an optical system for producing colored signal lights. The optical system includes an objective lens for projecting the colored signal lights through an aperture formed in the housing. A plurality of white light sources and elliptical reflectors for conveying light rays through associated colored filters for producing different color light rays. A plurality of dichroic mirrors angularly disposed in relation to the focal axis of the objective lens for intercepting the color light rays. The dichroic mirrors transmit certain color light rays and reflect other color light rays so that a given colored signal light is emitted through the aperture.

FIELD OF THE INVENTION 
This invention relates to a multiple color aspect signal unit, and more 
particularly to a searchlight signaling device, especially for railway 
signaling, which is capable of selectively providing luminous radiation of 
an initial color or one of a plurality of subsequent colors which have 
correspondingly higher frequency bands than the frequency band of the 
corresponding initial color. The signal device includes a metal 
weatherproof casing for housing the optical assembly. The housing includes 
a frontal opening which is covered by a plano-convex lens. The optical 
assembly includes a plurality of lamps for the generation of luminous 
radiation. A static color filtering system is interposed between the lens 
and the lamps. The color filtering system is capable of determining 
statically the chromatic characteristics of the light emerging from the 
plano-convex lens in the front of the housing. 
In certain known colored signaling devices or serachlight signaling units, 
the means for the generation of luminous radiation includes a single lamp. 
The lamp is capable of generating white or achromatic light which is 
focused at the focal point of the plano-convex lens by a polished 
reflector. In these known devices, the optical filtering system includes a 
movable screen which is disposed between the lens and the source of white 
light. The mobile screen is equipped with a given number of different 
colored filters or roundels. Each of the colored roundels is selectively 
interposed between the source of white light and the lens. The position of 
the mobile screen is achieved by means of a motor or relay drive mechanism 
which is also located within the housing. These previous signal devices 
must rely upon the transitional displacement by a mechanical device which 
is a distinct disadvantage. That is, in order to ensure correct operation 
and power signal display, it is assumed the dive mechanism is functioning 
properly. Thus, the correct positioning of the mobile screen which carries 
the colored filters is dependent upon the proper operation of the drive 
mechanism. Ergo, a breakdown or malfunction of the drive mechanism may 
result in a filter of the wrong color being positioned between the source 
of white light and the objective lens. The resulting consequence of such a 
failure in the moving parts of these previous signal devices may cause an 
erroneous less restrictive signal display. 
OBJECTS OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a new and 
improved railway searchlight signaling device which is free of the 
disadvantages of previous known signaling devices. 
A further object of this invention is to provide a novel multiple color 
signal unit having a high degree of reliability. 
Another object of this present invention relates to a light signal device 
for searchlight signaling, especially for a railway signal, capable of 
providing luminous radiation with an initial color and with a number of 
subsequent colors, which have frequency bands higher than the frequency 
band corresponding to the initial color. The device includes a support 
housing, a plano-convex lens installed in proximity to an opening in the 
housing. The means for generating luminous radiation is located inside the 
housing. An optical filtering system is interposed between the lens and 
the luminous generating means. The optical filtering system determines the 
chromatic characteristics of the light emerging from the opening of the 
housing through the lens. The optical filtering system includes (N+1) 
number of different colored filters and N number of dichroic mirrors where 
N.gtoreq.1. The dichroic mirrors being capable of reflecting the radiation 
energy having frequencies equal to or greater than the frequencies of the 
color passed by the associated colored filter and to transmit the rays 
having lower frequencies. The dichroic mirrors being arranged in fixed 
positions between the plano-convex lens and its focal point so that in 
looking from the focal point of the lens to the lens itself, the cut-off 
frequency of each dichroic mirror is less than or equal to that of the 
following dichroic mirror and greater than or equal to that of the 
preceding dichroic mirror. The means for generating the luminous radiation 
include a first source of light which is capable of being focused on the 
focal point of the lens a luminous radiation having the initial color, and 
N number of other sources of light, each capable of producing a luminous 
radiation, having a respective color of the N number of colors, at the 
point representing the virtual image of the focal point of the lens with 
respect to the dichroic mirror associated with the given color.

Referring now to the drawings and in particular to FIG. 1, there is shown a 
plano-convex lens 1, the focal axis of which is indicated by the character 
A. The objective lens 1 is preferably clear or colorless. A first 
elliptical dichroic reflector 2, consisting for example of a 
partially-silvered mirror, is arranged with the longer axis lying on the 
focal axis A of the lens 1. A source of white light, such as an electric 
lamp, 3 is located in a first focus of the reflector 2. The light source 
consists preferably of a halogen lamp. The focal point F of the reflector 
2 coincides with focal point of the plano-convex lens 1. A red colored 
dichroid filter 4 is located between the elliptical mirror 2 and the focus 
F of the projector lens 1. Thus the luminous rays which are generated by 
the lamp 3 and are reflected by the silvered reflector 2 will cross at the 
focal point F. The filter 4 may consist of a plastic or composite lens. 
As shown, a red dichroic filter or semitransparent mirror 5 is located 
between the focus F of the lens 1 and the lens 1, itself. It will be seen 
that the dichroic mirror 5 is disposed in a plane forming a 45.degree. 
angle with the focal axis A of the plano-convex lens 1. The red dichroic 
filter 5 is capable of transmitting light rays of a red color and of 
reflecting the light rays having higher frequencies than red light. In 
viewing FIG. 1, it will be noted that a second ellipitcal dichroic 
reflector or partially-silvered mirror 6 is located above the focal axis A 
of lens 1. A source of white light 7, also consisting preferably of a 
halogen lamp, is located at the first focus of the elliptical mirror 6. 
The other focus of the reflector 6 coincides with the point F.sub.1 
representing the virtual image of the focus F of the lens 1, with respect 
to the red dichroic mirror 5. Thus, the major axis of the elliptical 
reflector 6 is perpendicular to the focal axis A of the lens 1. A yellow 
dichroic colored glass filter 8 is disposed between the reflector 6 and 
the point F.sub.1. Accordingly, the light rays generated by the lamp 7 and 
reflected by the reflector 6 will cross at the focal point F.sub.1. 
As shown, a yellow dichroic filter of semitransparent mirror 9 is located 
between the red dichroic mirror 5 and the plano-convex lens 1. Thus, all 
the yellow light rays emanating from the focus F.sub.1 are reflected by 
the dichroic mirror 5 and pass through mirror 9 to reach the plane surface 
of the plano-convex lens 1. The yellow dichroic mirror or filter 9 is 
disposed in a plane forming an angle of 90.degree. with the plane 
containing the red dichroic mirror 5. As is well known, the yellow 
dichroic mirror 9 is capable of transmitting light rays of a yellow color 
or colors having frequencies lower than yellow light and is adopted to 
reflect any light rays having frequencies higher than that of yellow 
light. 
In viewing FIG. 1, it will be seen that a third elliptical dichroic 
relfector or mirror 10 is located below the focal axis A of lens 1. As 
shown, a source of white light 11, also preferably consisting of a halogen 
lamp is located at the first focal point of the elliptical mirror 10. The 
other focus of the reflector 10 coincides with a focal point F.sub.2 
representing the virtual image of the focus F of the lens 1, with respect 
to the yellow dichroic mirror 9. It will be noted that the major axis of 
the elliptical dichroic reflector 10 is situated perpendicular to the 
focal axis A of the plano-convex lens 1. A green dichroic colored glass 
filter 12, for example, a plastic type of filter lens which is interposed 
between the reflector 10 and the yellow dichroic so as to intercept the 
light rays which are generated by the light source 11 and which are 
reflected by the reflector mirror 10. 
The use of dichroic filters and reflectors reduces the heating effects of 
the infrared light rays which are produced by the white light sources. 
Now let us assume that an electrical current is only fed to the halogen 
lamp 3 so that the light generated by it is reflected by the reflector 2. 
The reflected white light is colored red by the glass filter 4. This red 
colored light traverses or passes through the dichroic mirror 5, the 
dichroic mirror 9, and impinges upon the plane face of the plano-convex 
lens 1. Thus, the objective lens 1 correspondingly emits a beam of red 
light from its convex face. In railway operations, a red signal light 
indicates an ensuing danger condition. 
Now if an electrical current is only fed to the halogen lamp 7, the emitted 
white light from this lamp is reflected by the reflector 6. The white 
light passes through the colored plastic filter 8 and assumes a yellow 
coloration. This yellow light strikes the red dichoric filter 5, which, 
for the yellow rays, acts like a mirror. The yellow rays are reflected and 
strike the yellow dichroic mirror 9, which transmits them to the plane 
face of the plano-convex lens 1. Thus, the convex surface of lens 1 emits 
a beam of yellow light which signifies a caution to oncoming traffic. 
Finally, if an electrical current is only fed to the halogen lamp 11, the 
white light emitted by this lamp is reflected by the mirrored reflector 
10. The white light passes through the green filter and emerges as a green 
light. The green light strikes the yellow dichroic filter 9 which, for 
green rays, acts like a mirror. The green ray is then reflected onto the 
plane face of the plano-convex lens 1, and emerges from the convex face of 
the objective lens 1. The emerging green light signals a clear or safe 
condition. 
A three color aspect searchlight signal device of this invention as 
described with reference to the schematic diagram of FIG. 1 can be 
physically constructed to take the form as illustrated in FIGS. 2 and 3. 
As shown in FIGS. 2 and 3, the light unit is mounted with a rigid 
protective housing or case 20. The upper front end 20a of housing 20 is 
provided with a cylindrical tubular lens barrel to which is secured the 
hood 21 which shields the lens 1 from the direct rays of the sun or the 
lights of oncoming vehicles. The forward open end 21a of the cylindrical 
barrel section 21 is inclined or slanted downwardly to minimize the 
effects of sunlight. A clear transparent cover plate or diffuser 22 is 
secured to the open end 21a of the tubular hood 21. 
As shown, the top of the signal housing 20 is provided with a pair of 
apertured sighting members 23 which are aligned coaxially so as to be 
usable for the alignment or correct positioning of the signaling device. 
In viewing FIG. 3, it will be seen that the inside of the housing 20 
supports a frame member 24 which carries the optical system of the light 
sources as described in the schematic diagram of FIG. 1. 
The lamps 3, 7 and 11 are electrically connected to a suitable source of 
power by a conventional type of control and operating system (not shown). 
The searchlight signaling device according to the present invention 
operates with intrinsic reliability. For example, if for any reason the 
yellow dichroic mirror 9 breaks, the signal device is no longer capable of 
providing the safe green signal. However, the signal device is still 
capable of producing the yellow and red signals which is indicative of a 
caution condition and an order to stop, respectively. In the railroad 
industry, the absence of a signal or a dark signal is synonymous to a 
dangerous red signal which signifies an order to stop. 
Now, if the red dichroic mirror 5 is damaged, then only the yellow caution 
signal is incapable of being conveyed to a passing train. The red signal, 
normally associated with more restrictive conditions and orders, is still 
capable of being produced. 
While highly unlikely, it is quite possible that both of the dichroic 
mirrors 5 and 9 may become broken or may be seriously deteriorated by 
water leakage or the like. Under this condition both the green signals or 
the yellow signals will be incapable of being emitted, but it will be 
possible to cast the red signal. 
The chromatic characteristics of the three different color signals put out 
by the signaling device described can be modified by changing the 
composition of the condensing or converging filters 4, 8 and 12. Further, 
in place of the yellow dichroic mirror 9, an orange dichroic mirror can be 
substituted. In this case, the green color signal put out by the signaling 
device will be more intensely green, and less bluish. In addition, the 
yellow light produced by the signalling device will have fewer green 
components and more red components. 
It will be appreciated that by changing the composition of the filters 4, 8 
and 12, and by appropriately selecting the colors of the dichroic mirrors 
5 and 9, it is possible to produce colored signals which have chromatic 
characteristics satisfactory for standard requirements, for example, of 
the administrations of the railway systems of most any country. 
Let us now refer to FIG. 4 which shows a schematic diagram of another 
embodiment of the optical system which is slightly different from that 
illustrated in FIG. 1. In this embodiment, the dichroic mirror 9, which 
may be either yellow or orange, is placed in a plane which is parallel to 
the plane of the dichroic mirror 5. The lamp 11, its associated elliptical 
reflector 10, and the green filter 12 are therefore located on the same 
side as the lamp 7, its associated elliptical reflector 6, and the yellow 
filter 8, namely with respect to the focal axis A of the plano-convex lens 
1. The mode of operation of the system illustrated in FIG. 4 is 
substantially the same as the mode of operation of the optical system in 
FIG. 1, and therefore need not be described in further detail. 
The optical schematic diagrams shown in FIGS. 1 and 4 may be modified in 
such a manner that the searchlight signaling device is capable of giving 
luminous signals in other colors. If, for example, it is desirable to have 
a four aspect signaling device which is capable of providing light rays 
having the colors of red, yellow, green, and violet, it is simply 
necessary to add a green dichroic filter to the optical system in FIG. 1. 
The dichroic mirror is placed in a plane which is parallel to the plane of 
the red dichroic mirror 5 and is positioned between the yellow dichroic 
filter 9 and the plano-convex lens 1. It is also necessary to pre-arrange 
a source of violet light at the point representing the virtual image of 
the focus F of the lens 1, with respect to the light yellow dichroic 
filter. This source of violet light can consist of a source of white 
light, an elliptical reflector and a violet colored filter. Similarly, the 
same result can be achieved by adding to the optical system illustrated in 
FIG. 4. That is, another light yellow dichoric filter can be arranged 
parallel to the dichroic filters 5 and 9. This added yellow dichoric 
filter is positioned between the dichroic filter 9 and the plano-convex 
lens 1. In this case, too, it is necessary to provide a source of violet 
light at the point representing the virtual image of the focus F of the 
lens 1, with respect to the green dichroic filter. Conversely, a two 
aspect signaling device may be realized by removing either mirror 5 or 9 
along with its associated source of white light, reflector and filter. 
From the above-described explanation, it is apparent that the structure of 
the searchlight signaling device according to the invention can be 
subsequently expanded to produce signaling devices capable of supplying 
light rays with a primary or one color and with N (N.gtoreq.1) of a 
secondary or other color. It will be understood that the frequencies of 
the secondary colors are higher than the frequency corresponding to the 
primary color. The signaling device includes a protective case for housing 
an N number of dichroic mirrors which are arranged between the focus F of 
the plano-convex lens and the lens 1, itself. In looking from the focus F 
to the lens 1, the filtering frequency of each dichroic mirror is less 
than or equal to that of the preceding dichroic mirror. A first light 
source is adapted to produce at the focus F of the lens 1, light rays of 
the abovementioned primary color. An N number of other light sources, each 
of which is capable of producing light rays at the point representing the 
virtual image of the focus F of the lens 1 with respect to a corresponding 
dichroic mirror. 
The light sources may be selectively located on one side of the focal axis 
A of the plano-convex lens, or alternately, may be disposed on opposite 
sides of the focal axis A. 
Naturally, as long as the principle of the invention remains the same, the 
forms and the details of the equipment may differ extensively from what 
has been described and illustrated purely by way of non-limiting examples, 
without, however; going beyond the scope of the present invention.