CA1288130C - Lights for vehicles - Google Patents

Abstract

IMPROVEMENTS IN LIGHTS FOR VEHICLES
ABSTRACT OF THE DISCLOSURE
A vehicle lamp for bicycles and the like is provided, having a compound reflector. The front opening is non-circular in shape, generally rectangular. The reflector itself has a plurality of nested sections that are stepped one from another, each lying on a surface of revolution generated by a different curve extending rearwardly from the front, each curve being generated from a common generating point in the vicinity of which an intended light source is to be held. One of the sections is defined by an empirically determined non-conic curve, and has a characteristic angularly unbroken reflected beam from a point source, which diverges in the far field but with a pattern of angular spread where intensity falls relatively sharply from the beam centre, so as to provide a central pool of light of relatively high intensity and an extended relatively low level intensity on either side. The other sections are similarly formed, but have another characteristic angularly unbroken reflected beam from a point source which diverges in the far field but with a pattern of angular spread where intensity falls relatively slowly from the beam centre.

Description

~ 2~38130 IMPROVEMENTS IN LIGHTS FOR VEHICLES
FIELD OF THE INVENTION
This invention is concerned with the design of reflectors for vehicle lights, especially but not 5 exclusively cycle lights. It i8 concerned with the efficient design of such lights in which the reflector and lens are of non-circular profile and also with the problem of providing illumination in the far field at high angles from the optical axis.
1o BACKGROUND TO THE INVENTION
Many commercial cycle lights are designed with a light-emitting area of circular cross-section and contain a circular section reflector usually of paraboloidal form.
Other types of cycle light are designed with a light-15 emitting area of rectangular cross-section and contain a circular section reflector which has been truncated to fit within the rectangular aperture of the light. The reflector is generally of paraboloidal for~. But in truncating the reflector optical efficiency is lost 20 becauae some sectiona of the reflector are 80 severely curtailed that the degree of subtense of the lamp at the reflector is much reduced.
A parabaloidal reflector has been the norm because it i8 forgiving of poor manufacturing tolerances and 25 ensures that all parts of the reflector contribute to the forward going beam. But it provides a reflected beam of no angular spread except that imparted by filament size ~.2~8130 and the light within the forward beam has a fixed spatial distribution heavily concentrated about the optical axis.
There are limitations on the pattern of far field angular distribution that can be straightforwardly achieved with 5 such a beam.
It is nearly always the case for cycle lights that the angular spread of light in the horizontal plane must be different to that in the vertical plane. Commonly, it is the cycle light lens that creates this difference after 10 acting upon an essentially circularly symmetric light beam from the reflector. Such a lens contains one or more arrays of lenticular or prismatic components 80 that the sum light bending power in one plane is different from that in the perpendicular plane. It is often a drawback of such lenses that their styling is unattractive. A
preferable alternative, particularly for front cycle lights which traditionally are preferred with a simple front lens, is for the reflector to create, at least in part, an asymmetry in the light beam.
A further light 1088 mechanism occurs when cycle lights are mounted on the bicycle's wheel mounting forks, because the angular spread of light from the cycle lights is usually large enough to cause a significant portion of the light to be blocked by that portion of the wheel 25 projecting beyond the forks.
A yet further problem in the design of a lens for a cycle front light is that the light source filament is ~ 2~8130 sufficiently reces6ed in a light housing that direct light from the filament cannot supply, at large angles from the optical axis of the light, the illumination required by the various international lighting standards. Such 5 standsrds require that cycle lights shall supply not only an intense central light beam but also a degree of illumination at large angles to the optical axis, defined by the centre of the central light beam. The luminous intensity required at these angles is usually sufficiently 10 low that it can be supplied as direct light from the filament. It is common for cycle lights to achieve the wide angle illumination by allowing direct light from the lamp filament to be seen either via a slot in the reflector or via a truncated circularly symmetric 15 reflector. Redirection of the light beam, for example, to increase the angle of emission from the cycle light, can be achieved by prismatic or lenticular structures in the front lens.
It i8 common for cycle rear lights to employ such a 20 reflector, together with a domed lens, in order to create the wide angle coverage. This is because a cycle rear light is required to illuminate a field of at least 180 degrees in the horizontal plane. Since the luminous intensity requirements of the central light beam are 25 modest, it is not too important for the reflector to maintain a high optical efficiency in collecting light from the filament and delivering it to the central light 81~0 beam. Cycle front light~, however, are required to provide a high luminous intensity central light beam and require the degree of light collection by the reflector from the lamp filament to be high. The need for a high 5 degree of light collection by the reflector of a front light usually ensures that it subtends a large solid angle at the lamp, and this feature prevents direct light from the lamp illuminating a sufficiently wide angle field even though the direct light from the lamp filament is sufficient to provide the required level of illumination at the wider angle. It is a further consequence of the large reflector subtense angle that the wide angle illumination, via a truncated or slotted reflector, is often not a viable compromise.
SUMMA~Y OF THE INVENTION
It is an object of the invention to design for a cycle or other vehicle light with a generally rectangular or other non-circular cross-section emitting area a reflector of generally rectangular cross-section which, in 20 producing the main beam from the light, operates with greater optical efficiency than a conventional reflector of circular cross-section which has been truncated to fit the cycle light aperture.
It i~ also an object of the invention to design a 25 reflector for a cycle or other vehicle light that with a given light source and battery pack produces a beam gpread that follows the general recommendations of lighting ~ ~8130 standards but is larger than existing cycle lights.
It is a further object of the invention to provide for a cycle or other vehicle light a reflector of generally rectangular cross-section which produces an 5 asymmetric output light beam from a compact light source.
It is yet another object of the invention to provide for a cycle light a reflector of generally rectangular cross-section for which in at least one direction perpendicular to the optical axis of one section of the 10 reflector the output light beam is confined within a narrow width for a sufficient distance beyond the cycle light 80 as to prevent light from the high intensity central portion of the output beam from being blocked by the bicycle wheel when the cycle light is mounted on the 15 bicycle's wheel mounting fork-c.
The invention provides a reflector for a lamp which reflector has a front opening of non-circular outline lying on one smooth unbroken surface, said outline defining generally orthogonal major and minor directions, 20 the reflector comprising a plurality of nested sections each divided from an adjoining section by a step and each lying on a surface of revolution generated by a different curve extending rearwardly from the front opening, each said curve being generated from a common generating point 25 in the vicinity of which an intended light source is to be held with an anterior section being defined by a region surrounding the aperture from which region opposed sectors 1~38130 extend to the front opening along the minor direction and with a broken posterior section being defined by a pair of sectors to opposed sides of the aperture extending to the front opening along the major direction, one of said sections being formed from an empirically determined non-; conic curve which has a characteristic angularly unbroken reflected beam from a point source which diverges in the far field but with a pattern of angular spread where intensity falls relatively sharply from the beam centre to 10 provide a central pool of light of relatively highintensity and an extended relatively low level intensity either side of the central pool, and the other of said sections being formed from an empirically determined non-conic curve which has another characteristic angularly unbroken reflected beam from a point source which diverges in the far field but with a pattern of angular spread where intensity falls relatively slowly from the beam centre.
The outline of the reflector may lie on a surface d-fined by a plane normal to the optical axis or on a surface defined by a cylinder whose axis is normal to the optical axis or on a smooth unbroken concave or convex spherical surface or on a toroidal surface, but is preferably on a cylindrical surface.
A single reflector section is defined as consisting of one or moro sub-sections or "regions", these regions being parts of a single generated profile exibiting 1288~30 6ymmetry about its optical axis.
A further object of the present invention is to overcome the problem of obt&ining a sufficiently wide angle of illumination.
According to another aspect of the invention, that problem is solved by using a reflector that provides a beam of reflected light from a compact source, said beam having gaps in the near field beam profile, and said reflector being employed in combination with a front lens 10 provided with diverting means such as lenticular or prismatic structures located in the near field beam gaps to spread incident direct light to the far field at angles beyond those where the reflector cuts off direct light.
According to a further aspect of the present 15 invention, there is provided a light for generating a field of illumination, the extremes of which are formed by direct light from the lamp filament, and in which the reflector has a subtense at the lamp which is sufficient to reduce the angular field of direct light from the lamp 20 to below the required angular field of illumination, ssid light comprisings a compact source of light:
a reflector consisting of two or more curved sections, said section~ either being edge-abutting or 25 8eparated by one or more further sections which subtend a negligibly small angle at the lamp, said reflector producing a light beam from the compact source of light ~ 2asl3~) which contains at least one deluminated area whic~ remains present in the near field light beam at least as far along the direction of the optical axis of said reflector as the reflector aperture rim; and a lens for spreading the light beam from the reflector, said lens containing at least one section which substantially overlays a deluminated portion of the light beam from the reflector, said section containing pri~matic and/or lenticular structures which in part deviate direct 10 light incident upon at least a first part of said section from the compact light source in order to illuminate the extreme portions of the field, and which in further part increase the angular spread of the direct light ~ncident upon at least another part of said section in order to 15 illuminate those parts of the field which would otherwise be deluminated because of the light deviation caused by the first part of said section.
It is an advantage of the aforesaid lamp arrangement that extreme field illumination is obtained without 20 adversely affecting the efficiency of production of the main beam of reflected light, and that the lenticular or prismatic elements of the diverting means do not substantially affect the light arriving at the lens from the reflector.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying ~ ~8130 drawings, in which similar parts are identified by the same reference numeral, and:-Figure 1 is an exploded view of a cycle light according to the invention;
Figure 2 is a cross-section of a conventional cycle light;
Figure 3 is a front perspective view of a conventional reflector for a cycle light of rectangular front profile;
Figure 4 is a front view of a first form of reflector according to the invention;
Figures 5 and 6 are cross-sections of the reflector on the lines A-A and B-B of Figure 4 respectively;
Figure 7 i8 a diagrammatic section of the reflector 15 Of Figures 4 to 6 illustrating its differences from a conventional reflector;
Figure 8 is a quartered front view of a reflector according to the invention showing its appearance with three sections, four sections and six sections;
Figure 9 is a front view of a reflector which to the right of the line A-A is the same as Figure 4 and to the left of the line A-A is of a further form;
Figure lO is a diagrammatic section of a reflector of the further form of Figure 8;
Figure 11 is a diagrammatic section of a yet further form of the reflector;
Figure 12 is a ray diagram showing embodiments of 12~8130 the reflector in which the reflected light beam converges before it diverges;
Figures 13 and 14 are diagrammatic sections of further reflectors showing the formation of gaps in the 5 pattern of reflected light;
Figure 15 is a front view and Figure 16 is a fragmentary section of a lens having areas for deviating incident direct light in regions where there are gaps in the pattern of reflected light;
Figure 17 i8 a diagrammatic ~ection of a reflector, lamp and lens showing the pattern of emergent light;
Figures 18-19 are respectively a section of the reflector of Figure 4 on the line B-B with a bulb in po~ition and a diagrammatic front view of the bulb showing 15 the filament and location details.
T~E PROBLEMS OF REFLECTOR DESIGN
The general kind of light with which this invention is concerned i8 shown in Figure 1. The light includes a compact light source 1 such as an electric lamp that i8 20 fitted in a reflector 2 that is generally rectangular in front view, and in plan has rearwardly curving upper and lower edges 7. The reflector 2 i8 moulded in polystyrene or other ~uitable plaJtics material and i8 aluminised. It i8 covered by means of a convex part cylindrical lens 25 a88embly 3, of a suitable clear plastics material whose shape is complementary to that of the reflector 2 and which is a push fit thereon.

~ 2~8130 A cross-section of a conventional cycle light is shown in Figure 2. A portion of the light emitted from a compact source 1 is collected by a reflector 2 and directed towards a beam-forming lens 3. Generally, the 5 reflector 2 possesses a parabolic cross-section in a plane containing its optical axis 4 so that the light from reflector 2 travels essentially parallel to the optical axis 4, as indicated by rays 5. Reflector 2 may also consist of two or more sub-sections that are circularly 10 symmetric about the optical axis 4 and have a common optical axis. The lens 3 contains an array of lenticular or primsatic elements, typically as shown by convex lenses 6, which serve to spread the uni-directional beam from the reflector 2 into an output beam of the required light 15 distribution and angular spread. Generally the reflector 2 and lens 3 are of circular front profile so that the reflector is well-matched if its aperture diameter is equal to that of the lens and operates with an efficiency principally determined by the minimum and maximum subtense 20 angles A and B of the source 1 at the reflector 2. But if the lens 3 i8 of rectangular front profile then either reflector 2 must have an aperture diameter which is no larger than the shorter side length of lens 3 or the reflector 2 must be truncated. If the lens is to be fully 25 illuminated, the former option requires that the reflector is other than paraboloidal or has a non-specular surface.
A truncated reflector is illustrated in Figure 3, where 12~3 181~30 the effect of the truncation is that the reflector loses surface in the two perpendicular sections C-C and D-D, and only remains fully in diagonal ~ection E-E. Thus, whereas the maximum subtense angle of the light source 1 with 5 respect to the optical axis 4 of the reflector is equal to the angle B, as also shown in Figure 1, the subtense angles at the side and end mid points of the reflector are reduced to F and G. Consequently, less light i~ collected from the source 1 and directed into the output light beam 10 than would be the case for a corresponding circular reflector.
A further problem in a conventional cycle light is that of obtaining a desired light distribution to wide angles from the optical axis. Particularly for a cycle front light the reflector 2 subtends a large useable semi-angle, typically up to 120-135 degrees at the source 1 so that an extreme ray Sa is correspondingly limited to an angle of from 45 to 60 degrees to the optical axis 4. For a cycle front light, international lighting standards 20 commonly require that illumination ~hould extend to angles of up to 80 from the optical axis 4 and for a cycle rear light the angle ig larger, at leagt 90, and it is common for the reflector to be either truncated or slotted to let dirct light pass from the lamp filament to the reguired 25 semi-angle.
THE COMPOUND REFLECTOR OF THE INVENTION
Referring to Figures 4, S and 6, a first form of a ~ 288~3(~

reflector according to the invention consists of four sections lO, Il, 12, 13 with a common optical axis 14 and a common focal point 15 at which a compact source 1 is sited. Each section lO, 11 and 12 has a surface that is 5 smoothly curved and that produces a far field diverging beam and the individual reflectors lO, 11 and 12 are so positioned as to fill as far as possible the rectangular aperture. With reference to the axis 14 the section 10 occupies an anterior position, section 11 is at an intermediate position and section 12 is at a posterior position. The curve of each section lO, 11 and 12 in a plane including the optical axis 14 is preferably an aspheric non-conic curve and can be generated numerically or by graphical means having regard to the reflectivity 15 and texture of the surface, the size, shape and luminous output of source 16 and the required angular and intensity distribution of light in the far field. Generally spea~ing the illumination produced by each section will be a bright central region of ~spot" illumination merging into a peripheral region of fainter "flood" illumination, and the beam from the reflector will produce both spot and flood illumination that diverges in the far field even from a point source at its generating point whereas the beam from a parabola i8 parallel when a point source is at 25 its focus. Accordingly the size of the "spot"
illumination produced in the far field by the reflector can be adjusted as well as the divergence of the "flood"

1~8130 illumination. Generally, but not nece68arily, the sections 10, 11 and 12 exhibit symmetry in a plane containing the optical axis 14. Angular increments and distribution of light entering the reflector are correlated with required angular increments and required distribution of light in the far field as known in the art and the empirical curve needed to produce the required far field light distribution is derived from known principles of geometrical optics (see for an example "The Optical Design of Reflectors", William B. Elmer, John Wiley &
Sons, New York, 1980 at page 226). The reflector has a non-circular (in this case oval) outline bounded by relatively long sides 7 that are straight when viewed from the front and convex when viewed in top or underneath plan and relatively short arcuate ends 8. The sides 7 and ends 8 lie .on a cylindrical surface having an axis perpendicular to the reflector optical axis. In an alternative version the ends 8 are straight viewed from the front and from the side of the reflector. The sides 7 and enda 8 of the reflector present a front opening having an aspect ratio of about 1.5:1 for a beam-forming lens assembly 3 and there is a rear opening 9 for receiving the light source 16.
The middle or "vertical" reflector section 10 comprises a relatively small area central region lOa that surrouncs the opening 9 and relatively large area upper and lower peripheral regions lOb defined by arcuate ~.288130 segments directed towards the reflector sides ? and each of 6mall angular extent with reference to the axis 14.
The reflector 10 serves to define a strong central beam of an appropriate vertical spread. Deluminated regions lOc 5 bound lateral edges of the peripheral regions lOb and lead to intermediate or "diagonal" reflector 11 that is divided into four separated regions lla each of relatively small azimuthal extent in the plane of ~igure 4. Although the reflector 11, if complete, would be larger overall than 10 the reflector 10, its curvature is similar to that of reflector 10 and it serves to collect additional light from the source 16 and direct it into the central beam.
The reflector 11 is bounded at its lateral edges opposite to the regions lOb of reflector 10 by deluminated regions llb that in turn lead to a pair of regions 12a of an outer or "horizontal" reflector 12 each of relatively large angular extent with reference to the axis 14 and each directed towards one of the refector ends 8. The back section 13 which is deluminated i~ preferably flat and 20 serves to support the other three sections 10, 11 and 12 and hold them in registration with each other. It will be noted that although the central section 10 has the central region lOa continuous with the peripheral regions lOb, the sections 11 and 12 are present only as 25 discontinuous front regions lla, 12a, the rear portions being non-existent behind the deluminated back section 13.
The light that would otherwise have gone to the non-16 ~Z 88130 existent central regions of 6ection6 11 and 12 isintercepted by the central region lOa as a forward beam so that the front-to-rear distance of the reflector can be reduced without 1088 of efficiency. As best seen in 5 Figure 5, the region lOa i6 forward of the plane of the deluminated back section 13 to enable the region lOa to act in the above way.
Section 13 is also illustrated in Figure 7, which is a simplified form of the section A-A shown in Figure 5.
10 Irrespective of whether thi~ section comprises a single flat surface, as shown at 13, or a multiplicity of surfaces, such as 17 (which may be used interchangeably), it preferably subtends an insignificantly small angle at the light source 16 and therefore remains substantially deluminated.
Figure 7 illustrates why the multi-6ectioned reflector of the invention i8 optically more efficient than a truncated circular aperture reflector. If the aspect ratio of the light emitting aperture is defined by 20 the limit line J-J in one direction and the limit line K-K
in the orthogonal direction then the truncation of the outer section 12 in the plane perpendicular to Figure 7 would reduce tho subtense angle of the reflector at the light source 16 from B to A. However, because the 25 reflector profile in the plane perpendicular to Figure 7 is in fact the section 10 (shown to its full e~tent in this plane by the broken line extension) the actual angle 17 ~.2881~3~

subtended at the light source is L, which is greater than B. Consequently, the optical collection efficiency of the reflector depicted in Figures 4 to 7 i8 greater than that depicted in Pigure 3, and, at the same time, the emitting 5 aperture of the reflector, as depicted in Figure 4, is substantially rectangular.
Currently, the requirements for the output beam pattern from a front cycle light are described by lighting standards such as BS AU 155 and IS0 6742. Products which 10 meet these standards or generally conform with their recommendations typically produce a centralised light beam pattern which, on a screen placed transverse to the optical axis, appears as a bright horizontal bar of light with about a 4:1 aspect ratio of horizontal to vertical 15 width. Typically, the pattern has transverse beam widths of approximately 8 degrees by 2 degrees in order to conform with the above standards. There is generally an insignificant amount of light outside the central bar, beyond that generated as direct light from the filament 20 itself and a degree of extended horizontal field side lighting.
When the cycle light is mounted on a bicycle and is angled down to meet the road, either from the handlebars or the front forks, the central beam pattern is spatially 25 lengthened and thus reduced in terms of illumination in the direction of bicycle travel but remains sub~tantially unaffected in the transverse direction. Even with this 18 l ~ ~8 l3~

lengthening the illuminated portion of the road in the direction of travel is usually very restricted and generally unsuitable for cycling on unlit roads.
It i8 the lighting levels required by the lighting 5 standards cited above that contribute to the over-compactness of the cycle light beam. For example, ISO
6742 requires that the luminous intensity of the beam centre should reach 400 candelas at the rated light output of the lamp used whilst also meeting a lower level 10 after a battery endurance test.
The spplicants consider that it is desirable for the area of light on the road to be significantly larger than the current central beam area, particularly in the direction of travel, and, in common with almost all task lighting, should not exhibit an abrupt cut-off at its edges. An aim of the present front light is to meet the recommendations of BS AU 155 and the ISO 6742 endurance te~ts with a large area light beam. Meeting the beam centre light output of ISO 6742 at the rated output of the 20 lamp i8 considered a secondary goal.
The following tables are short form listings of typical empirically determined curves that would provide a desirable pattern for the output light beam when a front lens is added. In the tables:
M - angle between input ray to reflector from light centre and the optical axis N ~ angle between reflected ray and the optical axis lg ~.X88130 (a positive value for N denotes an initial convergence to the optical axis) P = distance from light centre to the specified point on the reflector X = distance of specified reflector point from the rearmost extent of reflector measured parallel to optical axis Y = distance of specified reflector point from optical axis.
Dimensions are millimetres and degrees.
Vertical reflector (10 in Figure 4) M N P X Y
48.00 0.0 7.276 0.05.40~
57.77 0.64 7.914 0.6486.695 1566.72 0.90 8.685 1.4367.978 74.95 1.12 9.602 2.3769.273 82.93 1.3110.743 3.54610.661 90.77 1.5112.190 5.03212.189 98.59 1.7214.080 6.97113.922 20106.62 1.9916.681 9.64015.984 115.00 2.4820.451 13.51218.535 123.97 3.6026.354 19.59521.856 134.00 15.0836.075 29.92825.950 Diagonal reflector (11 in Figure 4) M N P X Y
65.31 1.41 12.480 0.0 11.339 71.63 1.73 13.423 0.982 12.738 5 77.76 2.02 14.525 2.132 14.194 83.71 2.31 15.814 3.480 15.718 89.61 2.60 17.358 5.096 17.358 95.51 2.92 19.232 7.058 19.143 101.45 3.36 21.552 9.490 21.124 10107.45 4.17 24.508 12.598 23.369 113.83 6.41 28.328 16.660 25.912 120.44 10.08 33.287 22.078 28.698 127.53 15.00 39.973 29.563 31.700 Horizontal reflector (12 in Figure 4) M N P X Y
74.17 1.85 19.108 0.0 18.383 78.66 2.35 20.276 1.225 19.880 83.09 2.78 21.594 2.614 21.438 2087.47 3.16 23.086 4.192 23.063 91.84 3.52 24.797 6.007 24.785 96.21 3.86 26.778 8.110 26.621 100.62 4.24 29.099 10.577 28.600 105.10 4.72 31.859 13.514 30.759 25109.68 5.58 35.185 17.063 33.129 114.39 7.48 39.209 21.404 35.709 119.28 14.97 44.025 26.~43 38.400 21 ~ 288130 The distribution of light within the ang~lar 6pread of the output beam (6emi-angle = NmaX~Nmin) is given by the ratio of the increment in collection 601id angle from the light 60urce (e.g. the 601id angle 6tep between 5 successive M value6) to the increment in output beam solid angle (i.e. the solid angle step between the equivalent N
value6), where 601id angle S is defined by S - 2 ~ (C08 Nl - cos N2) Nl and N2 being value6 of the angle between the reflected 10 ray and the optical axi6 corresponding to 6uccessive increments in M values.
In the above data the solid angle steps between successive M values is constant for each table. As an example, the ratio for the vertical reflector 10 between 15 48 and 57.77 degrees, for which the output beam angle varies from 0 to 0.64 degrees, is 2177, whereas the ratio for the horizontal reflector 12 between 74.17 and 78.66 degrees, for which the output beam angle varies from 1.85 to 2.35 degrees, is 238. Consequently, if the vertical 20 and horizontal reflectors 10, 12 were to have continuous rotational symmetry about the optical axis, then the horizontal reflector 12 would produce a beam intensity in the interval 1.85-2.35 degrees 9.15 times le83 bright than the beam from the vertical reflector 10 over the interval 25 0-0.64 degrees. In an alternative interpretation, if the light source 16 io both negligibly small and is isoradiant with a luminous intensity of 1 candela, the horizontal 22 ~ 2 ~8 13~

reflector beam intensity in the interval 1.85-2-35 degrees will be 238 cd and the vertical reflector beam intensity in the interval 0-0.64 degrees will be 2177 cd.
In the reflector above, and in the absence of the S direct light contribution, the relationship between the intensity in candelas of the reflected beam and angle N
from the optical axis for the three reflector sections and with a source of 0.907 cd in the far field (3-5 metres from the lamp) i8 a8 follOW8:

Angle N Vertical Diagonal Horizontal reflector reflector reflector _ 0-5 1749 - _ 1 . 1574 1.41 - 537 1.5 1185 528 1.85 - - 188 8 4 9.5 8 3.7 8.5 3.7 12.5 2.8 6.3 2.2 0.2 0.4 0.2 23 ~ ~813~

It should be noted with regard to the intensities quoted above that reflected light i6 present in those angular po6itions about the axis where the reflector section is itself present, 80 that truncation needs to be S ta~en into account in considering whether or not a section is contributing to intensity at a given position in the far field.
The effect of a practical light source is to reduce the central intensity, and redistribute light to a greater 10 or lesser extent over the range of angles N. In the above case a bow-shaped filament (described below) of the dimensions commonly found in cycle lights would reduce the beam centre intensity from the vertical reflector 10 (N s 0) to about 760 cd. This light effectively reinforces the 15 angular distribution of light up to about 4 degrees from the optical axis.
The effect of the light source filament size is also to cause the beam at any angle N to emanate from an extended area of the reflector, 80 that a degree of 20 surface form error can b~ tolerated without significantly affecting the far field beam continuity.
By both varying the ratio of solid angle of light collected from the light source over a given angular increment to the solid angle of light reflected by that 25 increment and defining the boundary angular values of the output increment, it i8 clear that a wide range of output beam widths and distributions of light intensity may be 24 1288~3~

obtained. However, due account must also be taken of the reflectivity and scattering properties, if any, of the reflector material, the source size, shape and positional tolerance, and the directionality of light emission of the 5 source for a full description of the output light beam from the reflector.
The aggregate far field light beam pattern from the reflector 2 alone i8 characterised by a generally elongated beam with a non-uniform relative distribution of 10 intensity in orthogonal directions transverse to the optical axis. Referring to Figure 4, the reflector sections 12 produce a beam elongated in the direction H-H
and having an intensity profile which i8 peaked in the centre, the reflector sections 10 produce a more compact beam of considerably greater relative central intensity, whilst reflector sections 11 produce an intensity profile between the two. The lamp filament, which is characteristically bow-shaped, is aligned to lie along the direction I-I. The light from each of the reflector 20 ~ection~ preferably generate~ a far field pattern which i8 in edge-abutment to the far field pattern from the other two reflector sections.
The lens 3 in front of the reflector 2 preferably spreads light only in the direction H-H. In this way the 25 beam pattern in the direction H-H is primarily determined by the lens 3 and by the reflector sections 12 whilst the beam pattern in the direction I-I is primarily determined ~ ~ 88~30 by reflector sections lO and the dimension of the lamp filament in this direction. The light from reflector sections ll primarily reinforce~ the vertical beam pattern from reflector section lO. Thus, it i~ seen that 5 the size and intensity distribution within the beam pattern in each of the two orthogonal directions may be designed essentially independently of each other.
It is preferred that the angular spread of light in the direction I-I should be comparable to the angular 10 spread of light in the direction H-H, but that the relative intensity distribution should be more gradual in the direction H-H than the direction I-I. In this way a good compromise is achieved between (a) the cycle light conforming with the luminous intensity recommendations of 15 the above lighting standards, for which H-H lying horizontal is the preferred mounting, (b) the light beam having a sufficiently high central intensity (preferably on the optical axis) with which to create a central localised pool of relatively high illumination, and (c) 20 creating area- of light extending beyond and behind the central pool of light in the direction of travel by which to see a greater distance along an unlit road than is the case with other cycle lights and to be seen by oncoming vehicles. An acceptably large area of illumination will 25 be produced for the cyclist irrespective of whether the cycle light is mounted on a bicycle's handlebars with I-I
lying in a vertical plane or on the front forks with 26 ~.28t'3~0 either H-~ or I-I lying in a vertical plane. The illumination of moæt use to cyclists is a pool of light on the road about 3-5 metres long by 1.2 - 1.5 metres wide when the light is angled down from a height of 0.5 metres 5 (fork mounting) or 1 metre (handlebar mounting) to strike the road about 3-5 metres ahead of the bicycle. The reflector 2 is designed to provide at least this pool of bright illumination with a gradual decline in illumination outside that pool and with distribution of light more 10 widely so that the light can be seen clearly from a distance and at an angle by a motorist or pedestrian observer. Clearly, because of the declination of the light beam optical axis 14 towards the road surface in normal use the lower illumination area behind the bright central pool may, by virtue of the inverse square law of illumination, be of a not too disparate brightness. In contrast, the area of lower illumination ahead of the central pool will appear proportionately dimmer but may dtill provide sufficient illumination for warning of any 20 hazards.
OTHER COMPOUND REFLECTORS
As more and more sections are incorporated within the reflector 80 more and more coverage of the rectangular aperture is achieved. Figure 8 illustrates the appearance 25 of the aperture for 3, 4 and 6 reflector sections. Thus in the lower part of Figure 8, an additional reflector section 140 consisting of four isolated regions 140a is 27 ~.~88130 provided, the regions 140a occurring between the reflector regions lla and 12a of each quadrant of the reflector. In the upper left hand quadrant there are additional reflector sections 141-143 having regions 141a-143a 5 located between the regions lOb and 12a. It will be noted that only the central reflector section 10 is continuous, all the remaining reflector sections 11, 12, 140, 141, 142 and 143 being truncated in their central regions where they pass through the plane of the deluminated back 10 section 13.
Figure 9 illustrates another form of the reflector.
To the right of the line H-H the reflector is the same as shown in Figure 4 whilst to the left of the line H-H it will be seen that the single flat deluminated section 13 of Figure 3 has been replaced by outer and inner flat deluminated areas 18 and 19 and reflector section 11 is continuous with an illuminated central region llc linking the peripheral regions lla rather than regions lla being isolated. Figure 10 shows a simplified section along the 20 line I-I in Figure 9. The reflector sections 10, 11 and 12 aro all prosent along this section, as compared to the presence of 10 and 12 only in the similar view shown in Figure 7. The sections 18 and 19 are sited such that they subtend a negligibly small amount of light from the source 25 20.
Because the reflector sections 10, 11 and 12 are e~sentially independent of one another in that their 28 ~.2 88130 profiles and angular extent need only be limited by the requirement that section 13 (Figures 4 to 7) or sections 18 and 19 (Pigures 9 and 10) subtend little or no light from the source, they can each exhibit different angular 5 spreads for the output light beam. In one preferred version of the reflector, sections 10 and 12 generate light beams from the light source which possess different angular light spreads and intensity distributions, whilst reflector section 11 possesses a similar output beam 10 profile to section 10. In another preferred version of the reflector, the profile of reflector section 10 on either side of its optical axis is not a smooth monotonic curve but contains two or more edge-abutting sub-sections.
An example of such a form of reflector section 10 is 15 illustrated in Figure 11. The reflector section consists of two sub-sections 21 and 22 which are edge-abutting at point 25. Both 21 and 22 have a common optical axis 23 and act 80 that light from the source 24 is converted into , overlaid or separate output beam~ by the reflectors.
LOCAL CONVERGENCE & FAR FIELD DIVERGENCE
For most existing cycle lights the reflector possesses a parabolic profile and therefore generally forms a highly collimated light beam with a Jmall degree of angular spread due in most part to the size of the J
25 light source filament. The lens in front of the reflector then creates a divergence to this beam by means of lenticular or prismatic arrays. Should a cycle light with 29 1;:~3813~) such a reflector and len6 assembly be sited on the wheel mounting forks of a bicycle then a significant portion of the light will be blocked by that part of the wheel which protrudes beyond the cycle light. This effect becomes 5 particularly noticeable with the small steering movements necessary to maintain the bicycle in motion.
Thus, in the preferred version of the reflector illustrated in Figure 4 at least one of the reflector sections is designed 80 that the greater part of the light 10 beam leaving it is initially convergent to points in the vicinity of the most forward-extending parts of the bicycle wheel and then starts to diverge to form its far field pattern.
Figure 12 illustrates one example of the convergence lS principle. The light from a source 26 strikes reflector sections 27 and 28. Three rays 29, 30 and 31 are shown leaving the outer reflector section 28. The outermost ray 29 converges towards the optical a~is 32 at a greater angle than the innermo~t ray 31. Consequently there is a 20 region at some di~tance beyond the reflector at which the light from reflector section 28 i8 confined to a width at most equal to that of the reflector as a whole. Up to that reqion the light reflected from region 27 will also be confined within the width of the reflector. The 25 convergence region is illustrated in Figure 12. Up to the line Q-0 the light from the reflector is confined within the width of the reflector as a whole. Preferably the 30 ~ Z~38130 central reflector region 27 in Figure 12 should exhibit covergence or divergence properties which confine the light leaving it to within the light beam leaving region 28 until position Q-Q in Figure 12 and preferably the 5 cycle light lens which is generally present in front of the reflector should not significantly affect the operation of the reflector as described with reference to Figure 12.
GAPS IN THE REFLECTED LIGHT
Figure 13 showc more clearly the position of a typical deluminated section 13. The rays 36 drawn from focus point 15 to the reflector sections 10 and 12 strike section 13 tangentially. Only the physical extent of the filament of lamp 16 in the direction of the optical axis 14 allows light from the filament to impinge upon section 13. As previously explained, the reflector sections 10, 11 and 12 are preferably not parabolic, and the outer limits of a typical fan of rays reflected from the section~ 10, 12 are shown a- 37, 38, 39 and 40. The 20 presence of doluminated aection 13 and the direction of the ray~ rofloctod by ections 10, 11 and 12 causes a gap in the overall reflected light beam profile to occur.
Thi~ gap is represented by 41 in Figure 13 and, depending on the rate of convergence of the rays 37 to 40, this gap 25 will extend for some distance beyond section 13.
Preferably, but not necessarily, the gap 41 extends at least to a line 42 drawn perpendicular to the optical axis 14 and touching the reflector at its rim. If the reflector were circularly symmetric about the optical axis 14 then the gap 41 would have the form of an annular ring.
In the preferred embodiment of the invention the reflector 5 is of the form shown in Figures 4 to 6 and has only limited rotational symmetry about the optical axis 14.
Consequently, the shape of the deluminated areas will be substantially the same as that of sections 13 as seen in Figure 4 and they will decrease in size at points further 10 along the optical axis at a rate determined by the convergence and/or divergence of the light from reflector sections 10, 11 and 12.
Figure 14 illustrates another multi-section reflector that produces a light beam with a deluminated section in its profile. The reflector consists of two sections 43 and 44 in edge-abutment. Light from a source 45 lying on the common optical axis 46 is reflected by sections 43 and 44 to form a light beam of which rays 47, 48, 49 and 50 are at the limits. Because there is a 20 divergence between rays 48 and 49 a deluminated gap 51 will appear and persist at all points furtber along the optical axis 46 from light source 45 until either ray 47 meet~ ray 50 or ray 49 meets ray 48, whichever occurs sooner.
LENS USING DIRECT LIGHT IN REGIONS WHERE REFLECTED
LIG M IS ABSENT
Figure 15 is a front view of the lens assembly 3 32 ~ X88~3~

which is generally similar to lenses used in most cycle front lights and mounted adjacent to the reflector. The len~ assembly 3, hereinafter referred to as the front lens, consists of a plurality of lenticular flutes 6 each 5 typically containing a subs'antially flat, or long radius of curvature, face on the outside and a short radius of curvature convex face on the side facing the reflector 2.
A cycle rear light would normally contain a plurality of spherically symmetric lenses in place of the lenticular 10 flutes 6.
According to the invention a section 54 consisting of a pair of regions 54a i8 located within the front lens 3 80 as to overlay the deluminated area 41 (Figure 13) or 51 (Figure 14) in the light beam created by the reflector.
The ~ection 54 has the purposes of (a) steering direct light from the lamp into a wider divergence than the angle between the rays 5a in Figure 2 which i8 the maximum angle that direct light can emerge from the reflector, and (b) replacing the coverage lost by that part of the incident 20 direct light that has been diverted to large angles from the axis 14 by e~tending the angular Jpread of a further portion of the direct light impinging on the section 54.
Figure 16 i~ an example of the profil. of prismatic and lenticular elements used in the lens 3. It is 25 preferable for these elements to be sited on the front lens face ad~acent to the reflector. Lenses 6 are the elements common to most cycle front lights and serve to 8~3~

both spread the main light beam arriving from the reflector and smooth out any structure caused by the lamp filament. Lens element 56 and prismatic elements 57, 58, 59 and 60 only receive direct light from the lamp 5 filament, this light incident in the general direction shown by arrow 61. The direct light incident on prismatic elements 57, 58, 59 and 60 strikes faces 62, 63, 64 and 65 respectively, preferably with a negligibly small amount striking the opposite faces externally. The light is 10 refracted by the faces 62 to 65 and leaves the lens 3 at an angle to the optical axis direction 68 of the reflector which is greater than its incident angle to the optical axis. For example, for face 63 an incident ray 66 is refracted and leaves the front lens as ray 67. Preferably the inclination of faces 62 to 65 with respect to the optical axis 68 of the reflector is different for each face, 80 that the beams of light deviated by each face leave the front lens at different angles. In this way the tot~l beam leaving the front lens by way of faces 62 to 65 20 will con8i8t of di8crete section~ incremented in angle.
It iB al80 preferred that the faces 62, 63, 64 and 65 are curved, preferably with a shallow concave curvature, in order to create a small degree of divergence to each discrete section of the beam leaving the front lens. __ 25 Thus, in the far field the discrete sections will overlap and form a continuous beam.
Lens element 56, which preferably contains a convex 813~

face which is inclined with it6 optical axis in the general direction indicated by the arrow 61, causes incident direct light from the lamp filament to be diverged in the far field after leaving the front lens 3.
5 ~y appropriate design of the lens parameters the divergence caused by the lens element 56 is sufficient to fill the range of angles not illuminated by direct light owing to the deviation by prismatic elements 57, 58, S9 and 60 whilst maintainng illumination in the direction 10 defined by lens element 56 and the filament of source 16.
To prevent colour fringes in the far field it is preferred that the other faces of prismatic elements 57, 58, S9 and 60 should be non-specular or frosted.
It is not essential that the prism elements 57, 58, 15 59, 60 and lens element 56 are arranged precisely as shown in Figure 16. There may be more or less prism elements and/or more lens elements, and they may be interspersed as desired. Conveniently the prism and lens elements 56-60 of Figure 16 are sited on the same pitch as lenses 53 in 20 Figure S, or a low multiple or sub-multiple thereof.
Figure 17 illustrates one arrangement of the reflector and lens that comprises the invention and the various light paths. A large proportion of the light from the source 16 is collected by the reflector sections 10 _' and 12 and i8 formed into a beam defined by the limit rays 37, 38, 39 and 40. Without the presence of the lens assembly 3 the far field beam would be divergent and ~5 ~ ~8~3t) defined by the limit rays 37 and 39. The effect of the lens elements 6 in the front lens 3 is to provide a small degree of beam spreading and smoothing to the reflector light beam as indicated by arow6 70. Deluminated section 513 of the reflector subtends a negligible amount of light at the lamp 16 and therefore give rise to deluminated ~ections in the reflector light beam. Within these sections are sited prismatic elements 57-60 and lens element 56 of the front lens 3, which receive only direct 10 light from the lamp 16. Some of this direct light is deviated by the prismatic element 57-60 into discrete beams 71 which form the extremities of the required angular field from the cycle light and which overlap in the far field if the filament 16 has sufficient size in 15 the plane of Figure 17 or if the incidence faces of prisms 57-60 are curved. A further portion of the direct light from light source 16 impinges upon lens element 56 and is ~pread over a range of angles depicted by lim$t rays 72 to illuminate an angular field defined by the subtense of 20 priBms 57-60 and lens 56 at the lamp filament 16. In this way there i8 full coverage of light from the optical axis 14 to the angular field extremities 71.
LIGHT SOURCE MOUNTING
It is desirable to take account of the size and 25 8hape of the light source in order to meet the output beam reguirements outlined above.
It is common for cycle light lamps to be of the 36 ~ 2 ~8130 prefocus type, the filaments of which generally consist of a bow-shaped or linear coil of fine wire. Figures 18 and 19 illustrate a typical cycle light lamp mounted in a reflector. The light source is typified by Philips' lamps 5 type PR2, PR6 and PR31, all of which have a P 13.5S
prefocus mount and consists of a base 91 and glass bulb 92 which contains the filament 93 mounted between two supports posts 94. Electrical contact i8 made between base 91 and an end pip 95. At the top of the base there is a flange 96 which contains at least three upstanding sections 97, and the distance from the top of these sections to the centre of the filament 93 is accurately maintained during manufacture. For the above lamps this distance is 6.35 mm with a bidirectional tolerance of 0.25 15 mm. The lamp is located in the reflector by abutment of upstanding sections 97 against a flat central surface 98 attached to the main reflector 99. In this way the lamp fialement is correctly positioned in the direction of the optical axis 100.
The flange 96 al80 contains a cut away section 101 which i~ in a pre~cribed orientation with respect to the length of the filament 93. The orientation of the flange 96, and hence the filament 93, with respect to the reflector 99 is determined by locating cut away 101 against a post 102 which is itself located in the reflector housing.

Claims (16)

1. A compound reflector for a lamp which reflector has a front opening of non-circular outline lying on one smooth unbroken surface, said outline defining generally orthogonal major and minor directions, the reflector comprising a plurality of nested sections each divided from an adjoining section by a step and each lying on a surface of revolution generated by a different curve extending rearwardly from the front opening, each said curve being generated from a common generating point in the vicinity of which an intended light source is to be held with an anterior section being defined by a region surrounding the aperture from which region opposed sectors extend to the front opening along the minor direction and with a broken posterior section being defined by a pair of sectors to opposed sides of the aperture extending to the front opening along the major direction, one of said sections being formed from an empirically determined non-conic curve which has a characteristic angularly unbroken reflected beam from a point source which diverges in the far field but with a pattern of angular spread where intensity falls relatively sharply from the beam centre to provide a central pool of light of relatively high intensity and an extended relatively low level intensity either side of the central pool, and the other of said sections being formed from an empirically determined non-conic curve which has another characteristic angularly unbroken reflected beam from a point source which diverges in the far field but with a pattern of angular spread where intensity falls relatively slowly from the beam centre.

2. A reflector according to claim 1, further comprising a broken intermediate section formed with pairs of sectors to each side of the sectors of the anterior section and extending to the front opening along oblique directions.

3. A reflector according to claim 1, wherein at least one planar deluminated region directed normally to the optical axis of one of the reflectors occurs between two adjoining sections.

4. A reflector according to claim 1, wherein at least one section is profiled so that light reflected therefrom converges towards the axis of the section before it diverges.

5. A reflector according to claim 1, wherein the anterior section is profiled so that light reflected therefrom converges towards the axis of that section before it diverges.

6. A reflector according to claim 1, wherein the optical axis of the several sections and centres of generation thereof coincide.

7. A reflector according to claim 1, that is generally rectangular when viewed from the front with an aspect ratio of about 1.5:1.

8. A reflector according to claim 1, wherein the anterior section produces the beam with the pattern of angular spread where intensity falls relatively sharply from the beam centre.

9. A reflector for a lamp having a front opening of non-circular outline and a rear face bounded by an aperture for receiving an intended light source, the reflector comprising a plurality of empirically determined aspheric non-conic nested sections producing, with a point source at a common generating point thereof, beams that diverge in the far field, at least one of which sections produces a reflected beam that converges before it diverges to the far field.

10. A light comprising a reflector, a lens in front of the reflector, and a compact light source; the shape of the reflector and the relative positions of the reflector and the light source being such that the light beam reflected from the reflector is discontinuous whereby portions of the light beam are relatively unilluminated as it passes through the lens: and diverting means provided in the lens to spread incident direct light to fill relatively unilluminated portions of the beam of light in the far field and at angles beyond those where the reflector cuts off direct light, said diverting means being located in an area of the lens through which the relatively illuminated portion of the reflected beam passes.

11. A light according to claim 10, wherein the diverting means comprises an array of lenticular or prismatic structures on the inner face of the lens.

12. A light according to claim 10, wherein the diverting means is an array of parallel prismatic elements of increasing distance from an optical axis of the reflector and having faces struck by incident direct light that are inclined to the optical axis at angles that increase from one prismatic element to the next with increasing distance from the optical axis.

13. A light according to claim 10, wherein the faces struck by incident direct light have slight cylindrical, concave or convex curvature.

14. A light according to claim 11, wherein the faces of the prismatic elements not struck by the incident direct light are frosted to minimize development of colored fringes in the far field.

15. A light according to claim 11, wherein the inner face of the lens is formed with a multiplicity of cylindrical lens elements disposed in an array across the lens in areas where the lens passes reflected light and the pitch of the lenticular or prismatic structures of the diverting means is the same as that of the cylindrical lens element or a low multiple or sub-multiple thereof.

16. A light according to claim 10, wherein second diverting means adjacent the first diverting means is arranged to spread direct light from the source over an angular field defined by the subtense of the first diverting means at the source so that there is full coverage of light from the optical axis of the reflector to the extremities of the far field.