Background of the invention

1. Field of the Invention

The invention concerns a lighting system for spotlights, projectors and enlarging apparatuses, which provides an intensive and uniform illumination of a given area at a given distance. It consists of a source of light, an auxiliary mirror and the main mirror. Another part of the system is a composite lens, consisiting of a net of individual converging lenses, which direct the light rays coming from the source into the required plane, where they create the light spot.

2. The Prior Art

There exist many lighting systems used as automobile headlights. These systems are usually made by a continuous parabolic reflector covered by a glass cover with diverging elements. The light source is a halogen bulb with two filaments; one is for distant lighting and the other one for subdued lighting with an inner diaphragm that allows limitation of the subdued light beam. In order to decrease the reflector's vertical size, the classical paraboloidal reflector was remodelled into the shape of a homofocal reflecting area in such a way that this reflecting area was divided into a system of discretely connected paraboloidal segments with the same optimized focal length. The need for another decrease of the headlight's size lead to a production of an ellipticdioptric system. Its reflector has a shape of a rotational or polyelliptic ellipsoid with three axes. In one of its focuses there is the filament of the bulb and in the second one there is a diaphragm. The planoconvex lens, situated in the second focus of the ellipse, directs the output light rays so that they are parallel with the optical axis of the system. This lens also

projects the diaphragm into the luminous background of the reflector. This process defines distribution of the subdued headlight's illumination.

Since there is a bulb with one filament, this system can be used for subdued light only. Therefore one more lamp of a similar or the same construction is necesarry for a distant lighting apparatus. This apparatus has a very small height and it creates subdued lighting of good intensity and homogenity with a sharp boundary between light cone and darkness. Another apparatus unit with an increased reach of subdued lighting has a reflector of the type with a freely formed reflecting area, which is continuous and closed in such a way that, without the influence of a covering glass, the reflector projects to the required space elementary images of a single filament bulb. Even without the diaphragm, it makes a boundary between darkness and light. Light output capacity of such a system proportionally increases with the strength of the reflector and it allows also the using of its lower part, what increases the efficiency. Nevertheless, for a distant lighting an extra apparatus is needed. By the use of the conception with freely formed reflecting area an improved projective elliptical dioptric system of the lighting apparatus is achieved. The original ellipsoid is remodelled into a general area with a higher amount of light beam in the non-diaphragmed part of the focal plane. The reflector is more open in its upper part and more closed in its lower part. The light ouput of such a system is much higher in comparison with the previous system.

Similar lighting systems can be used for different lighting purposes, e.g. in the health service, as spotlights used in stomatology. These systems consist of a known type of planary lighting device using mostly as light sources a halogen bulb, and a cold reflecting concave mirror. Its reflecting part is arranged as composite mirror, which directs the light spot into the required plane.

The main disadvantage of present automobile lighting systems consists in their low lighting effectiveness. Moving vehicles use the beam of light rays, reflected by differently shaped mirrors, and the luminous flux coming out of light source straight ahead is not used and is therefore often shaded. Dazzling effect is another big disadvantage of such a lighting device, since almost all systems used so far give out an intensive light coming from the filament of the bulb, which is visible from the space before the spotlight. Both sharp edge between light and darkness and the uniformity of light beam intensity are difficult to obtain, the consequence of which is rather complicated systems. The big size of these lighting devices and the pitch of their covering glasses make suitable aerodynamic designing of the front part of the automobile to be a rather difficult task.

Spotlights used in stomatology have similarly low light effectiveness. The light, coming from the light source, is directed to the front space and, therefore, stays unused. When the light is turned on, the light beam reaches also the patient's eyes and causes unpleasant dazzle. The dentist's mirror can also reflect unwanted light from different mirroring areas; thus the observed image can be disturbed. During some elemental operations, e. g. during preparation of the crown, the light, reflected from the metal, creates a certain kind of barrier between the preparation opening and the reflecting surface of the crown. This makes operation more difficult. The reflectors with a composite mirrors are relatively big; when the spotlight is adjusted into an inapropriate position, the dentist can easily interrupt the light beam with his head and decrease the amount of light coming out from the spotlights and shining onto the desired spot on patient's body.

If another optimal system, for example a system of condensors, is added to one of the systems mentioned and described above, the resulting system could be used for lighting of the first principal plane, in which a field of negative or positive filmstrip is inserted. Such field is

then projected, with the help of an objective, into the image plane. This lighting system is suitable mainly for projectors, slide projectors and enlarging apparatuses.

There are slide projectors of big formats with intensive light sources. Their structure and different luminance of the light source influence negatively the lighting uniformity of the plane of incidence. Therefore, such lighting systems contain optical parts with composite members, and instead of a simple convex mirror, a composite mirror is used. Moreover, between two deflecting mirrors an intermediate image-forming system, consisting of two plates with composite lenses can placed. For big format slides, a honeycombed condenser system, consisting of a composite lens, is normally used. There are also used lighting systems made with one of the honeycombs as a composite mirror. The mirror consists of groups of curved reflacting plates, placed in one plane. The disadvantage of these systems is their big size and high number of complicated optical elements, what is the cause of bigger loss of the luminous flux as well.

In slide projectors of smaller formats are for illuminating systems used both spherical mirror with a light source and lens condenser system with an aspherical element and a thermal filter. The disadvantage of such optical systems consists in the fact that the rectangular frame with film strip placed in the first principal plane, is lit by a beam of light of a circular shape, which causes a loss of luminous flux. The angle of the luminous flux is furthermore limited by the outer rays, caught by a spherical or aspherical condensor, and therefore this angle cannot be further increased.

In enlarging apparatuses, dedicated mainly to amateurs, mainly the light sources for large areas are used, particularly opal lamps with a lens condenser system, or lamps with elliptic reflecting area. In some enlarging apparatuses can be used an independent head for a colour photograph with its own light source, usually a halogen bulb

with a diverging system, a mixing chamber for continuously adjustable colour filtration with an adjustable density diaphragm. Yet, such systems have very little effectivity.

Objects of the invention

The present lighting systems are limited by the disadvantages just outlined. The subject matter of our invention consists in that the main mirror, whose optical axis is identical with the main optical axis, on which the light source with the auxiliary mirror is positioned, has its concave reflecting surface formed as a composite mirror. This composite mirror consists of a system of concave spherical mirrors, whose side walls touch one another and whose vertexes are arranged on the surface, which has a shape of a rotational conic section, having in the meridian plane a shape of a non-circle curve. The particular reflecting areas of the concave reflecting mirrors have such a focal length and such an angle of inclination of the optical axis that they create the optical image of a light source in the vertexes of the geometrically corresponding lenses of the composite lens, which consists of a network of individual lenses and which is also arranged on the main optical axis. Relevant elementar areas of the concave spherical mirrors are projected into the required plane of the light spot.

When looking in the direction of the main optical axis and in an imaginary plane perpendicular to the main axis, each concave spherical mirror shape corresponds to the contour of plane of the projected light spot. The concave spherical mirror are further arranged in zones. Radii of curvature of these mirrors in one zone are equal, but differ from those of another zone.

Individual lenses of the composite lens have the same shape and size and they maximally correspond to the shape and size of the field of vision of the light source. They are also arranged in zones, which can be shifted in a direction of the main axis. The radii of curvature of

lenses of one zone differ from the radii of curvature of lenses of another zone. Vertexes of all lenses are arranged in one plane, perpendicular to the main optical axis and their optical axes are parallel to the main one. Under these circumstances the lenses are planoconvex. The back surface of particular lenses of the composite lens can be for certain types of lighting systems inclined to their optical axes in order to create an optical . wedge. It is also possible to make the whole back surface of the composite lens concave. Alternatives of arrangement of composite lens described above lead to the directing of the light beam into a required plane.

In case of using the lighting system for projecting purposes, particularly in slide projectors and enlarging apparatuses, a system of condensers can be added to the lighting system, which directs the luminous flux to a plane, in which a slide is placed.

The main advantage of the invented lighting system consists in its illumination effectiveness at a uniform distribution of the light beam with minimal dazzling effect. The size of the system is very small both when using this new system as a source of straight light, e.g. for automobile headlights or medicine spotlights, and with an added condenser system.

Brief description of the drawings

Fig. 1 is a schematic picture of lighting system of an automobile headlight; Fig. 2 is a light spot of a lighting system of a distant headlight of an automobile for an illumination of a distant part of the highway; Fig. 3 is a light spot of a lighting system of the subdued headlight of an automobile for a subdued illumination of the highway viewed in the direction

A; Fig. 4 is a schematic picture of an optical system of

spotlight used in health service; Fig. 5 is a schematic picture of a lighting system for a big format slide projector; Fig. 6 is a schematic picture of a lighting system for a small format slide projector; and Fig. 7 is a schematic picture of a lighting system for an enlarging apparatus.

Detailed description of the preferred embodiment

Figure 1 schematically shows a lighting system for moving vehicles, especially an automobile headlight optical system. It consists of the light source 1., what is a single filament halogen bulb, placed on the main optical axis 0., on which is arranged an auxiliary mirror 2. as well. Another part of the system is the main mirror 2, whose optical axis 0. is identical with the main optical axis 0_. It is made as a composite mirror, formed by a network of concave spherical mirrors 31 of a rectangular shape, whose side walls tightly abut on each other and whose vertexes 22. are arranged in an imaginary plane, making an aspherical curve in the meridian plane, rotary symetrical around the optical axis fi. , identical with the main optical axis 0. Another part is a composite lens 4., placed at the main optical axis 0 _. as well. It consists of a system of converging lenses 4_1, which have hexagonal shapes. Again, their side walls abut tightly on each other. Their vertexes 42 _. are arranged in a common plane, perpendicular to the main optical axis 0., and their back walls 43. are bevelled, so that they make optical wedges. All optical axes __0 are parallel to the main optical axis 0..

Between the mirror 3. and the composite lens 4 _. a condition must be fulfilled that the foci of the lenses 41 and the foci of the concave spherical mirrors 1 make dot networks of the similar shape and that a ray, coming from the middle of the light source 1 after reflection from the vertex __ ^of the concave spherical mirror ϋ is directed towards the vertex ____ of the geometrically corresponding

lens 4_L. The lighting system is completed by a covering dioptrically neutral glass 10.

A beam of light rays, coming from the light source 1, including the part reflected from the reflecting surface of the auxiliary mirror 2., impinges onto the reflecting surface of the main mirror .3. Each of its concave spherical mirrors 31 creates an image of the light source 1 in the correspodning lens 4_1 of the composite lens 4., which projects the rectangular concave spherical mirror 21 at a given magnification to the plane of the light spot 6 Through this plane passes the beam of light rays in the shape of concave spherical mirrors 1 in the main mirror 2* The same amount of images as is the n_tmber of concave spherical mirrors 1 or the lenses 4_1 is concentrated here. This is valid both for distant headlights and for subdued headlights.

In Figure 2 can be seen the spot of a distant headlight of a car on a highway profile 6_1. This state is enabled by a proper arrangements of the back areas 42 of particular lenses l_ of the composite lens 4 _. .

Figure 3 shows the light spot of the subdued headlights. Out of the picture follows that there is a higher concentration of the light spots in the central part of the plane than in the outer parts. This is also reached by a proper arrangement of the back areas 2 of the composite lens 4 _. .

The main advantage of this headlight lighting system is its ability to reach a higher light effectiveness by using light rays reflected both from the main and auxiliary mirror and by a proper directing of the luminous flux to the required area. The luminous flux is directed only in the direction of the light spot without any disturbing and unnecessary lateral exposures. In a subdued headlight a very well confined border between light and dark areas and an optimally chosen light spot has been achieved. Such a headlight is also suitable for track vehicles, wheel vehicles and military vehicles, where there is a mechanical

diaphragm with particular openings placed behid the covering dioptrically neutral glass, to properly direct and dim the luminous flux according to requirements of the user.

In lighting sets for distant light, the light spot is concentrated into one figure. It is totally uniform and independent of the shape and division of light from the source. The dazzling effect on the on-coming cars or on oneself is decreased to a minimum level, as only the particular lit areas of the concave mirrors are projected into the plane of the light spot, while the intensive brightness of the light bulb filament doesn't create an image in the space in front of the headlight. The outer front dimension of the subdued headlight with a single-filament halogen light bulb is comparable with the projecting systems of the headlight Super-ED. When the lighting area of the light source is diminished, for example when using a gas discharge lamp, it is possible to decrease the front size of the headlight. The covering glass without diverging elements is optically neutral and allows to increase the vertical and horizontal angle of tilting. This faciliates the solution of the aerodynamical design of the whole headlight and, therefore, also of the front radiator cover of a car.

This idea of a lighting system with only slight changes is also suitable for medical use, especially for stomatology, as could be seen in figure 4. After proper adjustment of the concave mirrors 21 of the main mirror 2 and the lenses 43. of the composite lens 4 _. it is possible to have the whole back area of this composite lens 4. in the shape of plane. The plane of the light spot is then uniformly lit. In the distance of 900 mm its dimensions reach up to 125 x 140 mm, what is the optimal size for stamotology. In this case, the sharp boundary between the light and dark area is reached, and dazzling of the pacient is minimal.

The lighting system can also be used in many other areas where minimal dazzling and uniform lighting of the

luminous flux are needed, e.g. in television studios, in photographie studios, or work shops as theatre and film spotlights etc., where minimum dazzling and uniform illumination of the light spot in a given distance is being require .

If a condenser set is added to the above described lighting system, it may also be used for slide projectors or for projecting large size images, as shown in figure 5.

Such lighting system uses a high-pressure discharge lamp as the light source 1 , an auxiliary mirror 2 and an intermediate projecting set, containing the main mirror 2- which is formed by a system of concave spherical mirrors 21, and the composite lens 4., consisting of a system of lenses 43.. All these members are arranged on the main optical axis 0.. The whole system and also the relations among the particular members are similar to that of the lighting system used for headlights of automobiles or for medicals lamps. Only the back surface of the composite lens 4. is made as diverging. This system is linked up to the condenser system 5_, arranged on the main optical axis 0_. It is composed of two convex lenses, the back one of which is exchangeable according to the focal length of the used objective Z-

Rays coming from the middle of the light source 1 and later reflected from the centres of the concave spherical mirrors 33. of the main mirror 3_ come through the geometrically corresponding convex lenses 4_L of the composite lens 4. with a diverging lens and through a condensor system 5, inersect approximately the middle of the plane of the light spot 6_, where a slide is placed, which should be projected with help of the objective 7 to an image forming plane (not shown). In this system it is necessary that the ratio of the diameter of the outcoming light beam, coming from the composite lens 4_, to the distance of the condenser system f_ from the composite lens 4., is equal to or smaller than the value of the relative opening of the objective 1_. In the plane of the light spot

6 _. are again concentrated as many images of the concave mirrors 3_1, projected by the lenses 4_1 of the composite lens 4 _. , as is the n__raber of the concave mirrors 21 or the number of lenses 4_1. This results in using practically the whole luminous flux and at the same time in a uniform distribution of the light and in a short total length of the whole system.

As follows from figure 6, it is possible to use this system, after certain modifications, for small format slide projectors. The idea and the description are similar to the above described case. There are nevertheless certain differences in the construction of the main mirror 2- of the lens 4. and of the condenser system 5.. A halogen light bulb is used as the light source !L. The main mirror consists of rectangular concave spherical mirrors 21 of the same size, which are arranged in lines, the neighbouring lines being displaced half of the width of one mirror 21. The geometrical centres of the mirrors 21 make a network similar to the geometrical network of lenses _L1 of the composite lens 4.. These concave spherical mirrors 2! whose vertexes 32 are arranged on an aspherical surface and whose optical centres are identical with the geometrical centres, lie at different radii from the main optical axis 0.. At the same time these concave spherical mirrors 21 with the same foci form zones, spherical mirrors 21 from differnt zones having different foci, in order to project the light source 3. to the vertexes _%2. of the lenses _1, which are also arranged in zones, extended in the direction of the main optical axis 0.. The condenser system _> consists of more elements; the first element is a diverging one and is constructianally adapted in such a way that the main rays intersect approximately the centre of the plane of the light spot 6_ and that the whole light beam passes the objective 1_. The back lens is exchangeable. The light source 1 is then projected approximately in the middle of the objective 2 in a geometrical network, analogous to that of the main mirror 2, and of the composite lens in a surface, where the ratio

of the diameter of this ray bundle and the distance of the plane of the light spot j5 from this bundle is approximately equal to or smaller than the value of the relative opening of the objective J.

By the above described solution, higher luminous flux together with a uniformly lit plane of the light spot 6 _. with the inserted slide is obtained, regardless of the shape and distribution of the light on the lighting area of the light source 1.

This system is almost identical with a lighting system for enlarging apparatuses with the possibility of projecting, as is shown in figure Z- For slide projecting, the system turns through 90° to the horizontal plane. The light source 1 is a halogen bulb. The system is completed with mirror 2, which directs the light beams onto the vertical plane. The back element of the lens condenser 5. is exchangeable according to the type of the projecting objective Z- ^A piece of black and white or colour filmstrip or a slide is placed in the plane of the light spot 6.. Filters 9. for a colour photograph are placed near the composite lens 4_; when inserted, they change colour filtration. By a grey filter (not shown) and by a mechanical diaphragm (not shown) , the light density of white and colour light is regulated. The main mirror 2 has a reflecting layer, which allows heat radiation to pass through.

In this case too, a great intensity of light with the input power 50 W is reached together with the uniform distribution of light, what is, expecially for colour photograph, very important. Further advantage consists in that the system forms one structural unit both for magnifying black and white and colour photographs with a high luminous flux and for excellent slide projection.

The above described system provides some more possibilities of using of this newly designed lighting system, e.g., in the sphere of professional projecting and reprographical techniques.