GB2190479A - Improvements in lights for vehicles - Google Patents

Abstract

A light primarily intended for use for a vehicle such as a bicycle, including a reflector (2) which provides a beam of reflected light from a source (1). The beam has gaps, such as gaps (41), in its profile. The reflector (2) is used in combination with a front lens (3) provided with diverting means (6) to spread incident direct light to the far field at angles beyond those where the reflector (2) cuts off direct light.

Description

SPECIFICATION Improvements in lights for vehicles Field of the invention This invention is concerned with the design of reflectors for vehicle lights, especially but not exclusively cycle lights. It is 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 farfield at high angles from the optical axis.

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 emitting area ofrectangularcross-section and contain a circular section reflector which has been truncated to fitwithin the rectangular aperture ofthe light. The reflector is generally of paraboloidal form. But intruncating the reflector optical efficiency is lost because some sections of the reflector are so 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 is forgiving of poor manufacturing tolerances and ensures that all parts of the reflector contribute to the forward going beam. But it provides a reflected beam of no angular spread exceptthat imparted by filament size and the light within the forward beam has a fixed spatial distribution heavily concentrated about the optical axis. There are limitations on the pattern offarfield angular distribution that can be straight forwardly achieved with such a beam.

It is nearly always the case for cycle lights that the angular spread of light in the horizontal plane must be differentto that in the vertical plane. Commonly, it is the cycle light lens that creates this difference after acting upon an essentially circularly symmetric light beam from the reflector. Such a lens contains one or more arrays of lenticular or prismatic components so thatthe 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, particularlyforfront cycle lights which traditionally are preferred with a simple front lens, is for the reflectorto create, at least in part, an asymmetry in the light beam.

Afurther light loss 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 projecting beyond the forks.

Ayetfurther problem is the design of a lens for a cycle front light is that the light source filament is sufficiently recessed 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 bythevarious international lighting standards. Such standards 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 atthese angles is usually sufficiently 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 lightfrom the lamp filament to be seen either via a slot in the reflector or via a truncated circularly symmetric reflector.

Redirection of the light beam, for example, to increase the angle of em ission from the cycle light, can be achieved by prismatic or lenticular structures in the front lens.

It is common for cycle rear lights to employ such a 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 modest, it is nottoo importantforthe reflectorto maintain a high optical efficiency in collecting lightfrom the filament and delivering itto the central light beam. Cycle front lights, 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 filamentto be high.The need fora high degree of light collected bythe reflector of a front light usually ensures that it subtends a large solid angle atthe lamp, and this feature prevents direct lightfromthe lamp illuminating a sufficiently wide angle field even though the direct light from the lamp filament is sufficientto provide the required level of illumination atthe 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.

Summary ofthe invention It is an object ofthe invention to design for a cycle or other vehicle lightwith a generally rectangular or other non-circular cross-section emitting area a reflector of generally rectangular cross-section which, in 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 fitthe cycle light aperture.

It is also an object ofthe invention to design a reflector for a cycle or other vehicle light that with a given light source and battery pack produces a beam spread that follows the general recommendations of lighting standards but is larger than the 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 asymmetric output light beam from a compact light source.

It is yet another object ofthe invention to provide for a cycle light a reflector generally rectangular cross-section for which in at least one direction perpendiculartothe optical axis of one section of the reflector the output light beam is confined within a narrow width for a sufficient distance beyond the cycle light so as to prevent light from the high intensity central portion ofthe output beam from being blocked by the bicycle wheel when the cycle light is mounted on the bicycle's wheel mounting forks.

The invention provides a reflectorfor 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 minordirections,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 rearwardlyfrom 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 thefarfield butwith a pattern of angular spread where intensityfalls relatively sharplyfromthe beam centreto 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 farfield but with a pattern of angularspreadwhere angular spread where intensity falls relatively slowly from the beam centre.

The outline of the reflector may lie on a surface defined 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 atoroidal surface, but is preferably on a cylindrical surface.

Asingle reflector section is defined as consisting of one or more sub-sections or "regions", these regions being parts of a single generated profile exibiting symmetry about its optical axis.

Afurther object of the present invention is to overcome the problem of obtaining 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 nearfield beam profile, and said reflector being employed in combination with a front lens provided with diverting means such as lenticular or prismatic structures located in the nearfield 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 invention, there is provided a light for generating a field of illumination,the extremes of which are formed by direct lightfrom the lamp filament, and in which the reflector has a subtense at the lamp which is sufficient to reducethe angularfield of direct light from the lamp to below the required angularfield of illumination, said light comprising:: a compact source of light; a reflector consisting of two or more curved sections, said sections either being edge-abutting or separated 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 which contains at least one deluminated area which remains present in the near field light beam at least as far along the direction ofthe optical axis of said reflector asthe 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 prismatic and/or lenticular structures which in part deviate direct light incident upon at least a first part of said sectionfromthe compact light source in orderto illuminate the extreme portions ofthefield, and which in further part increase the angular spread ofthe direct light incident upon at least another part of said section in order to illuminate those parts ofthefield which would otherwise be deluminated because ofthe lightdeviation caused by the first part of said section.

It is an advantage of the aforesaid lamp arrangement that extreme field illumination is obtained without adversely affecting the efficiency of production of the main beam of reflected light, and that the lenticularor prismatic elements of the diverting means do not substantially affectthe light arriving atthe lens from the reflector.

Brief description ofthe drawings Embodiments of the invention with now be described, byway of example only, with reference to the accompanying 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; Figure2 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 frontview of a firstform of reflector according to the invention; Figures 5and 6 are cross-sections ofthe reflector on the lines A-A and B-B of Figure 43 respectively; Figure 7is a diagrammatic section of the reflector of Figures 4to 6 illustrating its differences from a conventional reflector;; Figure 8 is a quartered frontview of a reflector according to the invention showing its appearance with three sections, four sections and six sections; Figure 9 is a frontview of a reflector which to the right of the line A-A is the same as Figure 4 and to the left ofthe line A-A is ofafurtherform; Figure 10 is a diagrammatic section of a reflector of the further form of Figure 8; Figure 1 lisa diagrammatic section of a yetfurtherform of the reflector; Figure 12 is a ray diagram showing embodiments ofthe reflector in which the reflected light beam converges before it diverges; Figures 13 and 14 are diagrammatic sections offurther reflectors showing the formation of gaps in the 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 is a diagrammatic section of a reflector, lamp and lens showing the pattern of emergent light; Figures 18-19 are respectively a section ofthe reflector of Figure 4 on the line B-B with a bulb in position and a diagrammaticfrontview of the bulb showing the filament and location details.

The problems ofreflector design The general kind of light with which this invention is concerned is shown in Figure 1. The light includes a compact light source 1 such as an electric lamp that is flitted in a reflector 2 that is generally rectangular in frontview, and in plan has rearwardly curving upper and lower edges 7. The reflector 2 is moulded in polystyrene or other suitable plastics material and is aluminised. It is covered by means of a convex partcylindrical lens assembly 3, of a suitable clear plastics material whose shape is complementary to that of the reflector 2 and which is a push fitthereon.

Across-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 reflector 2 possesses a paraboliccross-section in a plane containing its optical axis 4so that the lightfrom reflector 2 travels essentially parallel to the optical axis 4, as indicated by rays 5. Reflector 2may also consist of two or more sub-sections that are circularly 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 distribution and angular spread.Generally the reflector 2 and lens 3 are of circular front profile so thatthe reflector iswell-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 angles A and B of the source 1 atthe reflec tor 2. But if the lens 3 is of rectangularfront 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 illuminated, the former option requires thatthe reflector is otherthan paraboloidal or has a non- specular surface.A truncated reflector is illustrated in Figure 3, where the effect of the truncation is thatthe reflector loses surface inthetwo perpendicularsections C-C and D-D, and only remains fully in diagonal section E-E. Thus, whereas the maximum subtense angle of the light source 1 with respect to the optical axis 4 ofthe 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 is collected from the source 1 and directed into the output light beam than would be the case for a corresponding circular reflector.

Afurther problem in a conventional cycle light is that of obtaining a desired light distribution to wide anglesfrom the optical axis. Particularlyfora cyclefront lightthe reflector 2 subtends a large useablesemi- angle, typically up to 120-135 degrees at the source 1 so that an extreme ray Sa is correspondingly limited to an angle offrom 45to 60 degrees to the optical axis 4. Fora cycle front light, international lighting standards commonly requirethat iilumination should extend to angles of to from the optical axis 4 and for a cycle rear lightthe angle is larger, at least 90", and it is common forthe reflectorto be eithertruncated orslottedto let direct light pass from the lamp filamentto the required semi-angle.

The compound reflector ofthe invention Referring to Figures 4,5 and 6, a firstform of a reflector according to the invention consists offoursections 10,11,12, 13 with a common optical axis 14 and a common focal point 15 at which a compact source 1 is sited.

Each section 10,11 and 12 has a surface that is smoothly curved and that produces afarfield diverging beam and the individual reflectors 10,11 and 12 are so positioned as to fill as far as possibletherectangular aperture. With reference to the axis 1 4the 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 10, 11 and 12 in a plane including the optical axis 14 is preferably an aspheric non-coniccurve and can be generated numerically or by graphical means having regard to the reflectivity and texture of the surface, the size, shape and luminous output of source 16 and the required angular and intensity distribution of light in thefarfield. Generally speaking 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 reflectorwill 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 is paraliel when a point source is at 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 ofthe "flood" illumination. Generally, but not necessarily, 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 farfield 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 (seeforan 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 straightviewed from the front and from the side of the reflector. The sides 7 and ends 8 ofthe 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 1 0a thatsurrounds the opening 9 and relatively large area upper and lower peripheral regions 1 Ob defined by arcuate segments directedtowardsthe reflector sides 7 and each of small angular extent with reference to the axis 14.

The reflector 10 serves two define a strong central beam of an appropriate vertical spread. Deluminated regions 1 Oc bound lateral edges of the peripheral regions 1 Ob and lead to intermediate or "diagonal" reflector 11 that is divided into four separated regions 11 a each of relatively small azimuthal extent in the plane of Figure 4. Although the reflector 11, if complete, would be larger overall than the reflector 10, its curvature is similarto that of reflector 10 and its 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 1 Ob of reflector 10 by deluminated regions 11 b that in turn lead to a pair of regions 1 2a 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 reflector ends 8. The back section 13 which is deluminated is preferablyflat and serves to supportthe other three sections 10, 11 and 12 and hold them in registration with each other. Itwill be noted that although the central section 10 has the central region 1 Oa continuous with the peripheral regions 1 Ob, the sections 11 and 12 are present only as discontinuous front regions 11 a, 1 2a, the rear portions being non-existent behind the deluminated back section 13.The lightthatwould otherwise have gone to the non-existent central regions of sections 11 and 12 is intercepted by the central region 1 Oa as a forward beam so that the front-to-rear distance of the reflector can be reduced without loss of efficiency. As best seen in Figures, the region 1 0a is forward of the plane ofthe deluminated back section 13 to enable the region 1 0a 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.

Irrespective of whether this section comprises a single flat surface, as shown at 13, or a multiplicity of such faces, such as 17 (which may be used interchangeably), it preferably subtends an insignificantly small angle at the lightsource 16 and therefore remains substantially deluminated.

Figure 7 illustrates why the multi-sectioned reflector of the invention is optically more efficient than a truncated circular aperture reflector. If the aspect ratio of the light emitting aperture is defined by 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 Figure7 would reducethe subtense angle of the reflector at the light source 16 from Bto A. However, because the reflector profile in the plane perpendicular to Figure 7 is in factthe section 10 (shown to its full extent in this plane by the broken line extension) the actual angle subtended at the light source is L, which is greater than B.Consequently, the optical collection efficiency of the reflector depicted in Figures 4to 7 is greater than that depicted in Figure 3, and, at the sametime,the emitting aperture ofthe reflector, as depicted in Figure 4, is substantially rectangular.

Currently, the requirements forthe output beam pattern from a front cycle light are described by lighting standards such as BS AU 155 and ISO 6742. Products which 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 lightwith about a 4:1 aspect ratio of horizontal to vertical 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 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 lengthened and thus reduced in terms of illumination in the direction of bicycle travel but remains substantially unaffected in the transverse direction. Even with this 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 is the lighting levels required bythe lighting standards cited above that contribute to the overcompactness ofthe 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 ofthe lamp used whilst also meeting a lower level after a batteryendurancetest.

The applicants 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 ofthe present front light isto meet the recommendations of BS AU 155 and the ISO 6742 endurance tests with a large area light beam. Meeting the beam centre light output of ISO 6742 at the rated output of the lamp is considered a secondary goal.

The following tables are shortform listings oftypical 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 (a positive value for N denotes an initial convergence to the optical axis) P = distancefrom light centreto the specified point of the reflector X = distance of specified reflector point from the rearmost extentof reflector measured parallel to optical axis Y = distance of specified reflector pointfrom optical axis.

Dimensions are millimetres and degrees.

Vertical reflector (10 in Figure 4) M N P X Y 48.00 0.0 7.276 0.0 5.407 57.77 0.64 7.914 0.648 6.695 66.72 0.90 8.685 1.436 7.978 74.95 1.12 9.602 2.376 9.273 82.93 1.31 10.743 3.546 10.661 90.77 1.51 12.190 5.032 12.189 98.59 1.72 14.080 6.971 13.922 106.62 1.99 16.681 9.640 15.984 115.00 2.48 20.451 13.512 18.535 123.97 3.60 26.354 19.595 21.856 134.00 15.08 36.075 29.928 25.950 Diagonai 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 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 21.124 107.45 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 87.47 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 30.759 109.68 5.58 35.185 17.063 33.129 114.39 7.48 39.209 21.404 35.709 119.28 14.97 44.025 26.743 38.400 The distribution of light within the angular spread ofthe output beam (semi-angle = NmaxNmin) is given by the ratio ofthe increment in collection solid angle from the light source (e.g.thesolid angle step between successive M values) to the increment in output beam solid angle (i.e. the solid angle step between the equivalent N values),wheresolid angle S is defined by S = 2n(cos N1-cos N1) N1 and N2 being values of the angle between the reflected ray and the optical axis corresponding to successive 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 48 and 57.77 degrees, forwhich the output beam angle varies from O to 0.64 degrees, is 2177, whereas the ratio for the horizontal reflector 12 between 74.17 and 78.66 degrees, forwhich the output beam angle varies from 1.85 to 2.35 degrees, is 238.Consequently, if the vertical and horizontal reflectors 10, 12wereto have continuous rotational symmetry about the optical axis, then the horizontal reflector 12would produce a beam intensity in the interval 1.85-2.35 degrees 9.1 Stimes less brightthan the beam from the vertical reflector 10 over the interval 0-0.64 degrees. In an alternative interpretation, if the lightsource 16 is both negligibly small and is isoradiantwith a luminous intensity of 1 candela, the horizontal 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 direct light contribution, the relationship between the intensity in candelas ofthe 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) is as follows:: Angle N Verticai Diagonal Horizontal reflector reflector reflector 10 11 12 0 1851 0.5 1749 1 1574 1.41 - 537 1.5 1185 528 1.85 - - 188 2 463 465 186 3 102 232 170 4 26 59 146 5 9 21 37 8 4 9.5 8 10 3.7 8.5 3.7 12.5 2.8 6.3 2.2 15 0.2 0.4 0.2 It should be noted with regard to the intensities quoted above that reflected light is present in those angular positions about the axis where the reflector section is itself present, so that truncation needs to be taken into account in considering whether or not a section is contributing to intensity at a given position in the farfield.

The effect of a practical light source is to reducethe central intensity, and redistribute lightto a greater or lesser extent over the range of angles N. In the above case a bow-shaped filament (described below) ofthe dimensions commonly found in cycle lights would reduce the beam centre intensity from the vertical reflector 10 (N = 0) to about 760 cd. The light effectively reinforces the angular distribution of light up to about4 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 ofthe reflector, so that a degree ofsurfaceform error can be tolerated without significantly affecting the farfield beam continuity.

By both varying the ratio solid angle of light collected from the light source over a given angularincre mentto the solid angle of light reflected by that increment and defining the boundary angularvalues ofthe output increment, it is clearthat a wide range of output beam widths and distributions of light intensity may be 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 source for a full description ofthe output light beam from the reflector.

The aggregatefarfield light beam pattern from the reflector 2 alone is characterised by a generally elongated beam with a non-uniform relative distribution of 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 is 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 l-l. The light from each of the reflector sections preferably generates a far field pattern which is in edge-abutmentto 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 beam pattern in the direction H-H is primarily determined by the lens 3 and bythe reflector sections 12 whilstthe beam pattern in the direction I-I is primarily determined by reflector sections 10 and the dimension ofthe lamp filament in this direction. The lightfrom reflector sections 11 primarily reinforces the vertical beam pattern from reflector section 10. Thus, it is seen that the size and intensity distribution within the beam pattern in each ofthe two orthogonal directions may be designed essentially independently of teach other.

It is preferred that the angular spread of light in the direction I-I should be comparable to the angularspread 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 l-l. In this way a good compromise is achieved between (a) the cycle light conforming with the luminous intensity recommendations of the above lighting standards, for which H-H lying horizontal is the preferred mounting, (bathe 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) creating areas of light extending beyond and behind the central pool of light in the direction of travel by which to see a greaterdistancealong an unlit road than is the case with other cycle lights andto be seen byoncoming vehicles. An acceptably large area of illumination will be produced for the cyclist irrespective of whetherthe cycle light is mounted on a bicycle's handlebars with l-l lying in a vertical plane or on the front forks with either H-H or I-I lying in a vertical plane.The illumination of most 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 (fork mounting) or 1 metre (handlebar mou nting) to strike the road about 3-5 metres ahead of the bicycle. The reflector 2is designed to provide at leastthis pool of bright illumination with a gradual decline in illumination outside that pool and with distribution of light more 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 14towardsthe 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 not too disparate brightness. In contrast, the area of lower illumination ahead of the central pool will appear proportionately dimmer but may still provide sufficient illumination forewarning of any hazards.

Othercompoundreflectors As more and more sections are incorporated within the reflector so more and more coverage of there ctangular aperture is achieved. Figure 8 illustrates the appearance of the aperturefor3, 4 and 6 reflector sections. Thus in the lower part of Figure 8, an additional reflector section 140 consisting of four isolated regions 1 40a is provided, the regions 1 40a occurring between the reflector regions 11 a and 1 2a of each quadrant ofthe reflector. In the upper left hand quadrant there are additional reflector sections 141 - 43 having regions 141 a - 1 43a located between the regions 1 0b and 1 2a.It will be noted that onlythe central reflectorsection 10 is continuous, all the remaining reflectorsections 1 1, 12, 140, 141, 142 and 143 being truncated in their central regions where they pass through the plane of the deluminated back section 13.

Figure 9 illustrates another form ofthe reflector. To the right of the line H-H the reflector is the same as shown in Figure4whilsttothe leftofthe line H-H itwill be seen thatthesingleflatdeluminated section 13of Figure 3 has been replaced by outer and innerflat deluminated areas 18 and 19 and reflector section 11 is continuous with an illuminated central region 1 1c linking the peripheral regions 1 1a ratherthan regions 1 la being isolated. Figure 10 shows a simplified section along the line I-I in Figure 9. The reflector sections 10,11 and 12 are all present along this section, as compared to the presence of 10 and 12 only in the similarview shown in Figure 7.The sections 18 and 19 are sited such thatthey subtend a negligibly small amount of light from the source 20.

Because the reflector sections 10, 11 and 12 are essentially independent of one another in that their profiles and angular extent need only be limited by the requirement that section 13 (Figures 4to 7) or sections 18 and 19 (Figures 9 and 10) subtend little or no light from the source, they can each exhibit different angularspreads 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 profile to section 10.In another preferred version ofthe 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 reflector section 10 is illustrated in Figure 11. The reflector section consists oftwo sub-sections 21 and 22 which are edge-abutting at point 25. Both 21 and 22 have a common optical axis 23 and act so that light from the source 24 is converted into overlaid or separate output beams by the reflectors.

Local con vergence & 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 small degree of angular spread due in most part to the size of the light source filament. The lens in front of the reflectorthen creates a divergence to this beam by means of lent icularor prismatic arrays. Should a cycle lightwith such a reflector and lens assembly be sited on the wheel mounting forks of a bicycle then a significant portion ofthe light will be blocked by that part of the wheel which protrudes beyond the cycle light. This effect becomes 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 so thatthe greater partof the light beam leaving it is initially convergentto points in thevicinity of the mostforward-extending parts of the bicycle wheel and then starts two diverge to form its far field pattern.

Figure 12 illustrates one example ofthe convergence 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 axis 32 at a greater angle than the innermost ray 31. Consequentlythere is a region at some distance beyond the reflector at which the light from reflector section 28 is confined to a width at most equal to that of the reflector as a whole. Up to that region the light reflected from region 27 will also be confined within thewidth ofthe reflector. The convergence region is illustrated in Figure 12. Uptothe line Q-Qthe light from the reflector is confined within the width ofthe reflector as a whole.Preferablythe central reflector region 27 in Figure 12 should exhibit covergence or divergence properties which confinethe light leaving itto within the light beam leaving region 28 until position Q-Q in Figure 12 and preferablythe 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 shows 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 tangentia l ly. Only the physical extentofthe filament of lamp 16 in the direction ofthe optical axis 14 allows lightfromthefilamentto 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 sections 10, 12 are shown as 37,38,39 and 4O.The presence of deluminated section 13 and the direction ofthe rays reflected by sections 10, 11 and 12 causes a gap in the overall reflected light beam profile to occur.This gap is represented by 41 in Figure 13 and, depending on the rate of convergence of the rays 37 to 40, this gap will extend for some distance beyond section 13. Preferably, but not necessarily, the gap 41 extends at least to a line 42 drawn perpendiculartothe optical axis 14 and touching the reflector at its rim. lf the reflector were circularly symmetric about the optical axis 14then the gap 41 would havetheform of an annular ring. In the preferred embodiment of the invention the reflector is of the form shown in Figures 4to 6 and has only limited rotational symmetry about the optical axis 14.Consequently, the shape ofthe 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 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 reflectorthat produces a light beam with a deluminated section in its profile. The reflector consists of two sections 43 and 44 in edge-abutment. Light fro a source 45 lying on the common optical axis 46 is reflected by sections 43 and 44to form a light beam of which rays 47,48,49 and 50 are at the limits. Because there is a divergence between rays 48 and 49 a deluminated gap 51 will appear and persist at all points further along the optical axis 46 from light source 45 until either ray 47 meets ray 50 or ray 49 meets ray 48, whichever occurs sooner.

Lens using direct light in regions where reflectedlightisabsent Figure 15 is a frontview of the lens assembly 3 which is generally similar two lenses used in most cyclefront lights and mounted adjacentto the reflector. The lens assembly 3, hereinafter referred to as the front lens, consists of a plurality of lenticularflutes 6 each typically containing a substantially 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 flutes 6.

According to the invention a section 54 consisting of a pair of regions 54a is located within the front lens 3 so asto overlay the deluminated area 41 (Figure 13) or51 (Figure 14) in the light beam created bythe reflector.

The section 54 hasthe purposes of (a) steering direct light from the lamp into a wider divergence than the angle between the rays 5a in Figure2which is the maximum angle that direct light can emergefromthe reflector, and (b) replacing the coverage lost by that part ofthe incident direct light that has been diverted to large angles from the axis 14 by extending the angular spread of a further portion of the direct light impinging on the section 54.

Figure 16 is an example ofthe profile of prismatic and lenticular elements used in the lens 3. It is preferable for these elements to be sited on the front lens face adjacent to the reflector. Lenses 6 are the elements common to most cycle front lights and serve to 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 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 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 greaterthan 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, so that the beams of light deviated by each faceleave the front lens at differentangles. In this way the total beam leaving the front lens by way of faces 62 to 65will consist of discrete sections incremented in angle.It is also 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. Thus, in the far field the discrete sections will overlap and form a continuous beam.

Lens element 56, which preferably contains a convex face which is inclined with its optical axis in the general direction indicated bythe arrow 61, causes incident direct light from the lamp filament to be diverged in the far field after leaving the front lens 3. By 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 57,58,59 and 60 whilst maintaining illumination in the direction 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 57,58,59 and 60 should be non-specular orfrosted.

It is not essential that the prism elements 57,58,59,60 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 patch as lenses 53 in Figure 5, our a low multiple or sub-multiplethereof.

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 is 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 defined by the limit rays 37 and 39. The effect ofthe lens elements6 in thefront lens3 isto provide a small degree of beam spreading and smoothing tothe reflector light beam as indicated by arows 70.Deluminated section 13 of the reflector subtends a negligible amount of light at the lamp 16 and therefore give rise to deluminated sections 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 light from the lamp 16. Some ofthis direct light is deviated by the prismatic element 57-60 into discrete beams 71 which form the extremities of the required angularfield from the cycle light and which overlap in the far field if the filament 16 has sufficient size in the plane of Figure 17 or ifthe incidence faces of prisms 57-60 are curved.Afurther portion of the direct lightfrom light source 1 6 impinges upon lens element 56 and is spread overa range of angles depicted by limit rays 72 to illuminate an angularfield defined bythe subtense of prisms 57-60 and lens 56 at the lamp filament 1 6. lnthiswaythere is full coverage of lightfrom the optical axis 1 4to the angularfield extremities 71.

Light source mounting It is desirable to take account of the size and shape ofthe light source in orderto meet the output beam requirements outlined above.

It is common for cycle light lamps to be of the prefocus type, thefilaments of which generally consist of a bow-shaped or linear coil offinewire. Figures 18 and 19 illustrate atypical cycle light lamp mounted in a reflector. The light source istypified by Philips' lampstype 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 is 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 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 also contains a cut away section 101 which is in a prescribed orientation with respectto the length ofthe filament 93. The orientation oftheflange 96, and hence the filament 93, with respecttothe reflector 99 is determined by locating cut away 101 against a post 102 which is itself located in the reflector housing.

Claims (19)

1. A compound reflectorfor 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 befined 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 thefar field butwith a pattern of angularspread where intensityfalls relatively sharplyfrom the beam centreto 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 farfield 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 ofthe sectors of the anterior section and extending to the front opening along oblique directions.

3. A reflector according to Claim 1 or 2, 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 any preceding claim, 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 any preceding claim, 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 any preceding claim, wherein the optical axes of the several sections and centres of generation thereof coincide.

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

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

9. A reflectorfor a vehicle lamp substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 and 4 to 6 or 8 or 9 of the accompanying drawings.

10. A reflectorfor a lamp having a front opening of non-circular outline and a rearface 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 pointthereof, beams that diverge in the farfield, at least one of which sections produces a reflected beam that converges before it diverges to the farfield.

11. A light comprising a reflector, a lens in front of the reflector, and a compact light source, wherein the profile of the reflected beam from the light source has gaps in it where it passes through the lens and divert ing means in the lens located in the reflected beam gaps spreads incident direct light to the farfield at angles beyond those where the reflector cuts off direct light.

12. A light according to Claim 11, wherein the diverting means comprises an array of lenticular and/or prismatic structures on the innerface ofthe lens.

13. A light according to Claim 11 or 12, wherein the diverting means is an arrayf parallel prismatic elements of increasing distance form an optical axis of the reflector and having f struck by incident direct lightthat are inclined to the optical axis at angles that increase from one prismatic element to the nextwith increasing distance from the optical axis.

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

15. A light according to Claim 1 wherein the faces of the prismatic elements not struck by the incident direct light are frosted to minimise development of coloured fringes in the farfield.

16. Alight according to any of Claims 11 to 15wherein the innerface ofthe 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 ofthe lenticular or prismatic structures of the diverting means is the same as that ofthe cylindrical lens element or a low multiple or sub-multiple thereof.

17. A light according to any of Claims 11 to 16, wherein second diverting means adjacent the firstdiverting 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 ofthe reflectortothe extremities of the farfield.

18. A light according to Claim 11, substantially as hereinbefore described with reference to and as illustrated in Figures 13to 17 of the accompanying drawings.

19. A light for providing 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 reduces the angular field of direct light from the lamp to below the required angularfield of illumination, said light comprising: a compact source of light; a reflector consisting oftwo or more curved sections, said sections either being edge-abutting or separated 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 which contains at least one deluminated area which remains present in the light beam at least as far along the optical axis of said reflector as the reflector aperture rim; and a lensforspreading 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 prismatic and/or lenticular structures which in part deviate direct 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 ofthe direct light incident upon at least another part of said section in order to illuminate those parts of the field which would otherwise be deluminated because of the lightdeviation caused by the first part of said section.