Lighting system

A lighting system having a high output lamp constituting an approximately point-shaped light source and a plurality of transparent shells disposed about the high output lamp, each of which shells has a central opening, an inner rim face about the opening and an outer rim face about the periphery of the shell. At least a major portion of the light emitted by the lamp is received by the inner rim faces of the shells and is transmitted by total reflection between the opposite side walls of each of the shells to and out of the outer rim faces of the shells, from which the light emerges.

BACKGROUND OF THE INVENTION 
The present invention relates to a lighting system which comprises a high 
output lamp constituting an approximately point-shaped light source, for 
example a metal halide lamp or a halogen incandescent lamp, and 
light-directing means which direct the light from the lamp. 
In known lighting units of this type, the means which direct the light to a 
particular desired area is normally a reflector which is located on the 
side of the lamp facing away from the area to be illuminated. 
Because of the extreme brightness of such high output lamps--for example, 
the output of a 250 watt metal halide lamp is 20,000 Lumen--the use of 
such lighting systems is restricted, for they must be located at a 
substantial distance from the area to be illuminated, and they must be so 
arranged that persons present in the illuminated area do not normally have 
the lighting system in their field of vision, for the reason that the 
extremely high luminance of such lighting systems is very unpleasant to 
anyone looking at the light source of the system. 
With regard to the prior art, it should be pointed out that the principle 
of the total reflection of light for the purpose of light conduction which 
principle is made use of in the lighting system according to the 
invention, is of course known per se. For example, glass filament bundles 
are used to conduct light. It is also known to attach individual glass 
rods, in the case of lighting units for living rooms and the like, for 
decorative purposes, with one end pointing towards the lighting unit and 
the other end consequently appearing as an independently luminous point. 
Finally, lighting systems are also known in which a fluorescent lamp is 
located in a cap, from which cap a sheet of glass-like plastic extends 
upwards and, at its upper end, is bent downwards again, so that the light 
issuing from the free rim surface of the plate of glass-like plastic is 
projected downwards. 
Totally reflecting light-conducting elements have not hitherto been 
employed in order to enlarge the apparently luminous surface of lighting 
systems comprising high output lamps, and in order to distribute the light 
from such a lamp over a particular determined area. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is, therefore, an object of the invention to broaden the field of use of 
lighting systems comprising such high output lamps which, because of their 
extremely high luminance, have hitherto only been of limited 
applicability. More particularly, it is an object of the invention to 
provide a lighting system of the type initially described wherein the 
light flux emanating from the lighting system is distributed over a 
relatively large, apparently luminous surface, whereby the dazzling effect 
of the light source can be substantially reduced. In doing so, the losses 
which can naturally never be completely avoided should be kept low in 
spite of the high degree of efficiency of high output lamps. 
According to the invention, these objects are attained, in a lighting 
system of the initially described type, by the improvement of the said 
light-directing means comprising a plurality of transparent shells 
disposed about the high output lamp, each of which shells has a central 
opening, an inner rim face about the said opening and an outer rim face 
about the periphery of the shell, at least a major portion of the light 
emitted by the said lamp being received by the inner rim faces of the 
shells and being transmitted by total reflection between the opposite side 
walls of each of the shells to and out of the said outer rim faces of the 
shells, from which the light emerges. 
The annular shells can consist, for example, of a highly transparent 
acrylic glass. Preferably, however, they consist of optical glass of 
highest attainable light transmission, of the kind used, for example, for 
spectacle lenses or camera objectives. 
In the lighting system according to the invention, as a rule, virtually all 
the light emitted by the lamp is collected by the inner rim surfaces of 
the transparent annular shells and is passed, by total reflection at the 
main surfaces (bordering on air), to the outer rim faces of the annular 
shells which faces are thereby made to appear light-radiating. The total 
outer rim faces are large compared to the luminous surface of the lamp, so 
that the apparently luminous surface is very greatly increased in the 
lighting system of the invention. Lighting systems according to the 
invention also do not interfere optically with the appearance of a room in 
which they are used, since, when the system is viewed from the side, the 
light source itself is rendered more or less invisible. 
The inner rim or terminal faces of the annular shells preferably extend 
substantially at right angle to the adjoining inner and/or outer sides of 
the shell and substantially perpendicular to the direction of the light 
incident on such rim faces. This means that the inner rim face of each 
annular shell should at all points be at least approximately at right 
angle to a radius extending from a light source (which corresponds 
approximately to a point source) to the inner rim face. The two totally 
reflecting longitudinal shell surfaces which surfaces adjoin the inner rim 
face and extend from the latter to the outer rim or terminal face of the 
particular annular shell should, in their zone adjoining the inner rim 
face, extend at least approximately parallel to the aforesaid radius. 
Since, in practice, it is advantageous to select annular shells which are 
not excessively thick, the above condition can be fulfilled without 
difficulty. As a rule, the annular shells will be from about 3 to 6 mm 
thick, even though narrower or thicker shells may be used in certain cases 
depending on the size and construction of the lighting system. 
The inner rim faces of the annular shells can to some extent deviate from 
the above-mentioned preferred arrangement. However, it is essential that 
if the main surface on one side of a shell, e.g. its outer side refracts 
the light incident thereon from the inner rim face, it should refract the 
light in a direction such that it impinges on the surface on the opposite, 
e.g. the inner side of the annular shell at an angle which is still so 
small that the light is subject to practically total reflection. 
Accordingly, the inner rim faces of the annular shells are preferably 
located in contact with each other to constitute, at least approximately, 
a zone of a rotational body, advantageously of a spherical surface which 
surrounds the center point of the light source in the lamp. Here again, 
deviations are of course possible. Thus, the inner rim faces of the 
annular shells are, for manufacturing reasons, advantageously parts of the 
enveloping surfaces of a cone, since such surfaces can be ground and 
polished relatively easily. 
In order that the configuration of the individual annular shell (viewed in 
axial planes extending through the common central axis of the lighting 
unit and of the shells), in the region near its inner rim face, coincides 
at least approximately with the direction in which the light, coming from 
the light source which has a certain finite dimension, is incident in the 
inner rim face, the latter face should be at a distance from the light 
source in the lamp which is at least equal to one and up to three times 
the dimension of the light source in the axial direction. 
As a rule, it is preferred that the annular shells should be of at least 
approximately constant thickness. This facilitates their design. However, 
some deviations are also possible. A gradual reduction in thickness from 
the inner rim face to the outer rim face should, as a rule, be avoided as 
it restricts the possibilities of total reflection, whilst an increase in 
thickness in the outward direction assists total reflection. In order to 
increase the apparently luminous outer terminal face of a shell, the 
thickness of the annular shell can be increased in the region near the 
outer rim face so that the profile of the annular shell expands in that 
region, e.g. approximately in a trumpet-like manner. This does not 
substantially increase the amount of material required to make the annular 
shell, nor the weight of the lighting unit, while the apparently luminous 
surface can be increased considerably in this way. Furthermore, this 
arrangement makes it possible to distribute the light, emitted by the 
particular annular shell, over a larger area. 
In a particularly simple embodiment of the lighting system according to the 
invention, the other rim faces of the annular shells extend substantially 
vertically to the adjoining regions of the shells. In that case, the mean 
direction of light radiation to the apparently luminous outer rim face of 
each annular shell coincides everywhere with the central axis 
perpendicular to this surface. If, however, the outer rim face of the 
annular shell is inclined away from the aforesaid mean direction of light 
radiation, the main direction of radiation of the outer rim face can be 
thus deviated. Moreover, the apparently luminous outer rim face will 
thereby appear larger. 
In order to achieve special lighting effects, the outer rim faces of the 
annular shells can also be profiled in a manner suitable to attain the 
desired effect. 
Preferably, the annular shells are constructed, and arranged, in 
rotationally symmetrical configurations about the lamp. In that case, the 
outer rim faces of the annular shells are, in their preferred embodiment, 
conically beveled annular rim faces. The outer rim faces can, however, 
also possess a concave or convex curvature, so that their section in a 
plane extending through the longitudinal axis of the lamp is a concave or 
convex curve. This feature can be also used to vary the direction of light 
emission and the distribution of the light over a larger or smaller area. 
The annular shells need not necessarily be, or need not be throughout, of 
rotationally symmetrical configuration. For example, to distribute the 
light over rectangular areas, the annular shells can be of such shape that 
whilst their inner rim faces are true partial conical enveloping rim 
faces, the outer rim faces may extend substantially along rectangles, in 
particular along squares. In that case the annular shells are, for 
example, in the shape of a cloister dome or pyramidal surface with 
preferably rounded corners and/or edges. However, such shapes are 
relatively expensive to manufacture. 
As a rule, the annular shells will be vaulted in a cup-like manner, so that 
the annular shells which are furthest forward, in the principal direction 
of emission of light from the system, have approximately the shape of cups 
having an open bottom and with a relatively steep wall near the outer, 
peripheral rim, whilst the middle annular shells have approximately the 
shape of bowls with openings in their bottoms, and the annular shells 
which are set back furthest with regard to the principal direction of 
light emission extend, in axial section, initially away from the principal 
emission direction and only curve in towards this direction in their more 
outwardly-located parts, e.g. in a mushroom head-like configuration. 
Frustoconical configurations are also possible, though a vaulted dish- or 
cup-shape is as a rule preferred. It will be appreciated that, viewed in 
axial section, the annular shells must not be more strongly curved than is 
required for attaining the desired total reflection at both the inner and 
the outer main surface of the annular shell. The thinner the annular 
shell, the more it can also be curved, and still attain this end. 
While unsymmetrical shells are also possible, these will only be selected 
if the considerable technical effort required by their manufacture is 
justified by a special application. 
In order to achieve optimum quality of the lighting systems according to 
the invention, the outer and inner rim faces, and the two main surfaces, 
of each annular shell can be given optimum configuration, and be provided 
with optimal optical properties, by grinding and polishing. In the case of 
lighting units for less stringent demands it will usually be sufficient to 
manufacture both the inner and the outer main surfaces of the annular 
shells by a synthetic plastics molding techniques. However, even then it 
is advisable to finish the rim faces by machining, for example by 
grinding. 
In the lighting systems according to the present invention, it is, in 
principle, possible to use an arc lamp as high output lamp; however, it is 
preferred that the high output lamp used therein is one, the light of 
which is generated in a sealed glass bulb.

DETAILED DESCRIPTION OF THE EMBODIMENTS SHOWN IN THE DRAWINGS 
The lighting system shown in FIG. 1 is intended for the illumination of 
enclosed spaces, although lighting units according to the invention can 
also be used with advantage in the open, for example for illuminating 
roads, football fields and the like areas. 
The lighting unit is of rotationally symmetrical construction relative to 
its longitudinal axis 1 which is in vertical position if the unit is 
suspended from the ceiling. However, the unit can also be employed with 
the axis inclined at any angle to the vertical. 
The lighting unit is carried by a tubular suspensing rod 2, which 
accommodates a high voltage cable for supplying the current to a lamp 3. 
At the lower end of the suspending rod 2 a cylindrical casing sleeve 4, 
which is preferably made of metal, is affixed in a conventional manner to 
rod 2 concentrically therewith by means of appropriate threaded nuts. In 
addition, a lamp socket 5 for the lamp 3 is attached in a conventional 
manner at the lower end of the suspending rod 2; in the particular 
embodiment illustrated in FIG. 1, this lamp can be a 250 watt mercury high 
pressure lamp as supplied, for example, by OSRAM AG, Berlin, Germany. The 
luminous part of the light source of the lamp 3 is of approximately 
cylindrical shape and is indicated by reference numeral 6. This light 
source 6, which is of generally cylindrical shape, is the approximately 
point-shaped light source required in the lighting system for the purposes 
of the invention. 
The casing sleeve 4 has venting bores 7 at its top end wall, whilst at its 
bottom wall it possesses a cylindrical seat 8 in which a glass shell 
carrier 9 is suspended by means of four bayonet catches 9a, in the manner 
shown in the drawing. The glass shell carrier 9 comprises an upper 
open-ended sheetmetal cylinder 10 and four carrier plates 11 the upper 
ends 11c of which are welded to the rim at the lower open end of cylinder 
10. The carrier plates are uniformly distributed about the periphery of 
cylinder 10 and lie in planes which pass through the central axis 1 of the 
system. The carrier plates 11 consist of metal and have the contours of a 
segment of a circle, with the corners cut off. They are arranged in such a 
manner that the curved outer rims 11a of the carrier plates 11, which face 
away from the axis 1, lie in the surface of a hypothetical sphere which is 
concentric with the center of the light source 6 in the lamp 3. Inside the 
carrier plate 11, there extends a glass cylinder 14, the upper end of 
which surrounds the bulb 13 of the lamp 3. This cylinder 14 is made of a 
glass which absorbs the main portion of the infrared component of the 
light generated in the lamp 3. The cylinder 14 is seated with its lower 
rim on the upper rim 16a of a metal cylinder 16 which surrounds the lower 
part 13a of bulb 13 of the lamp 3 and which is welded onto the lower ends 
11b of the four carrier plates 11. On its outside, the metal cylinder 16 
is provided with a fine threading onto which is screwed a further metal 
cylinder 17 to the top of which is fastened a supporting ring 18 which is 
also made of metal. This supporting ring 18 supports the seven lower glass 
shells 21 to 27 whilst the six upper glass shells 28 to 33 rest by their 
inner rim faces 34 on the curved outer rims 11a, forming part of the 
above-mentioned spherical surface, of the four carrier plates 11. The 
level of the carrier ring 18 can be adjusted very accurately by 
appropriately turning the cylinder 17, which possesses an internal 
threading, upward so that the lower seven glass shells 21 to 27 come to 
rest with their inner rim faces securely against the curved outer rims 11a 
of the carrier plates 11. Since the carrier plates 11 are devised to 
achieve precise centering, their outer rims 11a are finished by grinding, 
so that they precisely form part of the hypothetical sphere, the center of 
which is identical with the center of the light source 6; in the preferred 
embodiment, shown in FIG. 1, this sphere has a diameter of 80 mm. 
The inner rim faces 34 of the annular shells 21 to 33, which shells consist 
of optical glass, each form parts of conical surfaces enveloping the 
last-mentioned sphere, but because of the small thickness of the annular 
shells the total surface covered by them approximates sufficiently to the 
surface of the above-mentioned sphere; consequently, the four carrier 
plates 11 hold the annular shells 21 to 38 accurately centered around the 
light source 6. At the same time, the two circular edges at the upper and 
the lower ends of the inner rim face 34 of a given annular shell in each 
case abut the corresponding edges of the rim faces 34 of the two adjacent 
annular shells, one above and the other below the first-mentioned given 
shell, whereby, virtually all the light emitted by the light source 6 is 
collected by the assembly of the inner rim faces 34 of all of the annular 
shells 21 to 33. The small amount of light which passes from the light 
source 6 to the circular area enclosed by the upper edge of the inner rim 
face 34 of the uppermost annular shell 33 and to the circular area 
enclosed by the lower edge of the inner rim face 34 of the lowermost 
annular shell 21 is negligible since, with the type of lamp preferably 
used in this lighting system, only the surface of the jacket 6a of the 
cylindrical light source 6 is luminous. If there is used instead a lamp 
having a light source which is uniformly luminous in all directions, the 
top and bottom areas not covered by the inner rim faces 34 of the annular 
shells must be kept as small as possible. 
It will be seen that the light emitted from the cylindrical jacket of the 
light source 6 is incident onto each of the inner rim faces 34 in such a 
way that the direction of incidence of the light encloses only a very 
small angle with the two main surfaces 35 and 36 of which the former is 
the top or outer surface and the latter is the lower or inner surface of 
the corresponding annular shell and which surfaces form the upper and the 
lower edge, respectively, at the particular inner rim face 34. As a 
result, this light is in each case totally reflected as the two main 
surfaces 35 and 36 of the respective annular shell, until it is re-emitted 
from the shell through the outer rim face 38 of the latter. To make this 
possible, the distance of the inner rim faces 34 from the light source 6 
must be the greater, the larger the light source itself. 
In the portion of the glass shell 29 shown on the left-hand side of FIG. 1 
there have been indicated the light rays which are emitted respectively 
from the top and bottom zone of the light source 6 and enter through the 
inner rim face 34 of shell 29. FIG. 1 shows how these rays are deflected 
downwards through the vaulted shape of the shell 29, until they leave this 
shell in the desired downward direction. In addition, the two outermost 
rays of the light cone leaving the shell 29 have been indicated by 
outwardly deflected arrows in FIG. 1. 
In the embodiment shown in FIG. 1, the light rays leave the outer rim faces 
21a to 38a, of each shell in a relatively steep downward direction, 
whereby a person working in the room but not looking directly into the 
lighting system from below, will not be dazzled or blinded by this light. 
By varying the degree of curvature of the individual annular shells it is 
possible to allow the light being emitted downward to do so at any desired 
angle. 
It will furthermore be appreciated, from the above-described embodiment, 
that the direction and distribution of the light leaving each shell can be 
substantially influenced by giving an appropriate shape to the outer rim 
face 38 of the shell. 
FIG. 2 shows in partial view a somewhat modified embodiment of the novel 
lighting system. In the system shown in FIG. 2, the separate carrier 
plates for carrying and orienting the annular shells 40 arranged around 
the light source 6 of the lamp 3 have been replaced by an annular carrier 
element, serving for centering the shells. This carrier is a highly 
transparent glass cylinder 41, of which the outer surface, which carries 
the annular shells 40, is formed as a double frustocone the smaller 
frustoconical end faces of which are the end face 41a and 41b of the 
cylinder 41. The inner cylindrical wall 41e bears threadings by means of 
which it engages at its upper end a threading 10a on the outside of the 
lower end wall of metal cylinder 10 and at its lower end a threading 16b 
on the outside of the upper end of metal cylinder 16. Cylinder 14 is 
omitted. Centering of shells 40 is effected on the conically tapered 
surfaces 41c and 41d, which are rotationally symmetrical relative to the 
central axis 1 of the system. Correspondingly, the inner rim faces 42 of 
the annular shells 40 are not precisely at right angles to the line 
connecting their centers with the center of the light source 6. This 
slight deviation from a right angle can, however, be tolerated. 
The lighting systems shown in FIGS. 3 and 4 are of a type wherein only the 
lower six annular shells 50 project the light which is emitted by the 
light source 52 and received by their inner rim faces 51, in a downward 
direction, whilst the upper five annular shells 53 project the light 
transmitted by them upwards against the ceiling of a room illuminated by 
this system, or against a reflector of the like device (not shown). 
Furthermore, in the case of the six lower annular shells 50 shown in FIG. 
3, the outer rim faces 55 through which the light is emitted are not at 
right angles to the two main surfaces of each particular annular shell. 
Instead, the outer rim faces 55 extend in planes which are perpendicular 
to the central axis 54 of the lighting system. In this way, the light 
emitted by shells 50 is more specifically projected downwards, the 
apparent luminous surface and scattering of the light are increased. 
Finally, the lighting system according to the invention may have the outer 
rim faces of the individual annular shells designed to exhibit a 
rectangular, preferably a square configuration. In this case, each annular 
shell is approximately in the shape of a cloister dome with rounded edges. 
Such a shape is particularly appropriate if the lighting system is to 
illuminate a rectangular area.