EP0267268A1 - Lights for vehicles - Google Patents

Abstract

A headlight primarily intended for use in a vehicle such as a bicycle, comprising a reflector (2) forming a beam of light reflected from a source (1). The beam has voids, such as voids (41), in its profile. The reflector (2) is used in combination with a front lens (3) provided with a diverging member (6) which diffuses the incident direct light directed far away at angles situated beyond those where the reflector (2) cuts direct light.

Description

LIGHTS FOR VEHICLES

FIELD OF THE INVENTION

This invention is concerned with the design of reflectors f or vehic le lights , e specia lly but not exclusively cyc l e l i ght s . I t is concern ed wi th th e efficient design of such lights in which the ref lector 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. 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 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 form. But in truncating 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 al l 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 e spa a distribution heavily concentrated about the optical axis.

There are limitations on the pattern of far field angular distribution that can be straightforwardly 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 different to 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 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 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.

A yet further problem in 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 ill umination required by the various international lighting standards. Su ch standards require that cycle lights shall supply not only an int en se c entral l ight b eam b ut a l so 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 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 fi la ment to be seen ei ther via a s lot i n th e reflector or via a truncated circu larly symm etric 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 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 beam. Cyc e ront l ght s , however , are re qu ired to provide a high luminous intensity central light beam and require the degree of light collection by the ref lector from the lamp fi lament to be high. The need for a high 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 d irect l i ght from the lamp fi la ment i s sufficient to provide the required level of illumination at the wider angle. It is a further consequence of the large ref lector subtense angle that the w ide angle illumination, via a truncated or s lotted reflector, is often not a viable compromise. SUMMARY OF THE INVENTION

It is an obj ect 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 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 is al so an object of the 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 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 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 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 of the 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 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 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 whi ch 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 li ght of re l ativ ely hi gh 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 .

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 a toroidal surface , but is preferably on a cylindrical surface. A single reflector section is defined as consisting of one or more sub- sections or "regions ", these regions being parts of a single generated profi le exibiting 7 symmetry about its optical axis.

A further 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 ref lector 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 provided wi th diverting means su ch as lenticu l ar 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 fu rther aspect of the pres ent invention, there is provided a light for generating a field of illumination, the extremes of which are forme -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 to below the required angular field of illumination, said light comprising: a compact source of light; a re flector cons i s t ing of two or more curved sections, said sections either being edge-abutting or separated by one or more further sections which subtend a negligibly s ma ll angle at the lamp, said ref l ector producing a light beam from the compact source of light 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 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 of the 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 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 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 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 is a diagrammatic section of the reflector 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 10 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 er es before it diverges;

Figures 13 and 14 are diagrammatic sections of further 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 of the reflector of Figure 4 on the line B-B with a bulb in position and a diagrammatic front view of the bulb showing the filament and location details.

THE PROBLEMS OF REFLECTOR 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 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 is moulded in polystyrene or other suitable plastics material end is aluminised. It is covered by means of a convex part cylindrical lens assembly 3, of a suitable clear plastics material whose shape is complementary to that of the reflector 2 and which is a push fit thereon. A cross-section of a conventional cycle light is shown in Figure 2. A portion of the light emitted from a compact source 1 i s col lected by a re f lector 2 and directed towards a beam-forming lens 3. Generally, the 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. Ref lector 2 may 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 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 angles A and B of the source 1 at the reflector 2. But if the lens 3 is 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 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 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 section E-E. Thus, whereas the maximum subtense angle of the light source 1 with 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 is collected from the source 1 and directed into the output light beam 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 5a 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 commonly require that illumination should extend to angles of up to 80° from the optical axis 4 and for a cycle rear light the angle is larger, at least 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 required semi-angle.

THE COMPOUND REFLECTOR OF THE INVENTION

Referring to Figures 4, 5 and 6, a first form of a reflector according to the invention consists of four sections 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 a far field diverging beam and the individual reflectors 10, 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 10, 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 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 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 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 is parallel 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 of the "flood" 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 ends 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 10a that surrounds the opening 9 and relatively large area upper and lower peripheral regions 10b defined by arcuate segments directed towards the reflector sides 7 and each of small 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 10c bound lateral edges of the peripheral regions 10b and lead to intermediate or "diagonal" reflector 11 that is divided into four separated regions 11a 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 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 10b of reflector 10 by deluminated regions lib 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 is prefelably flat and 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 10a continuous with the peripheral regions 10b, the sections 11 and 12 are present only as discontinuous front regions 11a, 12a, the rear portions being non-existent behind the deluminated back section 13. The light that would otherwise have gone to the non- intercepted by the central region 10a 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 Figure 5, the region 10a is forward of the plane of the deluminated back section 13 to enable the region 10a 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 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-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 Figure 7 would reduce the subtense angle @f the reflector at the light source 16 from B to A. However, because the reflector profile in the plane perpendicular to Figure 7 is in fact the 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 4 to 7 is greater than that depicted in Figure 3, and, at the same time, the emitting 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 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 light with 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 direction of travel is us ua lly very res tri ct ed and generally unsuitable for cycling on unlit roads.

It is the lighting levels required by the lighting standards c i ted above that contr ibute to the ov er- 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 after a battery endurance test.

The applicants consider that it is desirable for the area of light on the road to be significantly larger than the current centra l beam area , pa rti cular ly 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 tests with a large area light beam. M eeting the beam centre light output of ISO 6742 at the rated output of the lamp is 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 (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 0.0 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

1 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 agona re ec or n F gure

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 of the output beam (semi-angle » N_max-N_mi_n) is given by the ratio of the increment in collection solid angle from the light source (e.g. the solid 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), where solid angle S is defined by

S = 2 TT (cos Ni - cos N )

M^ and N₂ being values of the angle between the reflected r y 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, 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 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 less bright than the beam from the vertical reflector 10 over the interval 0-0.64 degrees. In an alternative interpretation, if the light source 16 is both negligibly small and is isoradiant with a luminous intensity of 1 candela, the horizontal 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 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) is as follows:

Angle N Vertical 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

5 taken 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 * 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 fi lament size is al so to cause the beam at any angle N to emanate from an j extended area of the re f lector, so that a degree of 20 surface form error can be 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 is clear that a wide range of output beam widths and distributions of light intensity may be o a ne . ow er, ue accoun mus a en o e 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 of the output light beam from the reflector.

The aggregate far field 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 re flector 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 l amp f i l am ent , whi ch i s characteristically bow-shaped, is aligned to lie along the direction I-I. The light from each of the reflector sections preferably generates a far field pattern which is 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 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 by re flector sections 10 and the di mension of the lamp filament in this direction. The light from ref lector sections 11 primari ly rein forc e s the vertical beam pattern from reflector section 10. Thus, it is s een that 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 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 the above lighting standards, for which H-H lyirig 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) creating areas 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 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 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 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 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 still provide sufficient illumination for warning of any hazards.

OTHER COMPOUND REFLECTORS

As more and more sections are incorporated within the reflector so more and more coverage of the rectangular aperture is achieved. Figure 8 illustrates the appearance 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 provided, the regions 140a occurring between the reflector regions 11a and 12a of each quadrant of the reflector. In the upper l e ft hand quadran t the re ar e addit i ona l reflector s ect ions 141 -143 hav ing reg ions 141 a- 143 a located between the regions 10b 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 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 lie linking the peripheral regions 11a rather than regions 11a 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 similar view shown in Figure .^ The sections 18 and 19 are sited such that they 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 4 to 7) or sections

18 and 1 9 (Fi gures 9 and 10 ) subtend little or no light from the source, they can each exhibit different angular spreads for the output light beam. In one pre ferred version of the ref lector, s ections 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 of the reflector, the profi le 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 ref lector section 10 is 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 so that light from the source 24 is converted into overlaid or separate output beams by the reflectors. LOCAL CONVERGENCE & FAR FIELD DIVERGENCE

For most existing cy c le lights the ref l ector possesses a parabolic profile and therefore generally forms a highly colliraated light beam with a small degree of angular spread due in most part to the si ze of the light source filament. The lens in front of the reflector then create s a diverg ence to thi s beam by mean s of lenticular or prismatic arrays. Should a cycle light with such a re flector and lens as sembly be si ted 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 effe ct becomes particularly noticeable with the small steering movements necessary to maintain the bicycle in motion.

Thus, in the preferred version of the re f l ector illustrated in Figure 4 at least one of the ref lector sections is designed so that the greater part of the light 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 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. Consequently there 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 the width of the reflector. The convergence region is illustrated in Figure 12. Up to the line Q-Q the light from the reflector is confined within the width of the reflector as a whole. Preferably the 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 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 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 sections 10, 12 are shown as 37, 38, 39 and 40. The presence of deluminated section 13 and the direction of the 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, dependin 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 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 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 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 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 REFLECTED

LIGHT IS ABSENT

Figure 15 is a front view of the lens assembly 3 which s genera y s m lar to lenses used in most cycle front lights and mounted adjacent to the reflector. The lens assembly 3, hereinafter referred to as the front lens, consists of a plurality of lenticular flutes 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 as to overlay the deluminated area 41 (Figure 13 ) or

51 (Figure 14) in the light beam created by the reflector. The section 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 is the maximum angle that direct light can emerge from the reflector, and (b) replacing the coverage lost by that part of the 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 of the 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 l ight bea m ar ri ving 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 rec ei ve d i re ct l i ght f rom the l amp 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 external ly. The l ight 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 greater than its incident angle to the optical axis. For example , for face 63 an incident ray 66 i s refracted and leaves the front lens as ray 67. Preferably the incl ination of faces 62 to 65 with respect to the optical - axis 68 of the ref lector is different for e-ach face, so that the beams of light deviated by each face leave the front lens at different angles. In this way the total beam leaving the front lens by way of faces 62 to 65 will 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 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. 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 maintainng 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 or frosted.

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 pitch as lenses 53 in Figure 5, 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 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 of the lens elem ents 6 in thr front lens 3 is to provide a small degree of beam spreading and smoothing to the 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 ri se to delum inated sections in the re f l ec to r l ight be a m . W i thin th e s e sections are sited prismatic elements 57-60 and lens element 56 of the front lens 3 , which receive only direct light f rom the lamp 16. Some of this direct light is deviated by the prismatic element 57-60 into discrete beams 71 which form the ex trem iti es of the required angular field 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 if the incidence faces of prisms

57-60 ar.e curved. A further portion of the direct light from light source 16 impinges upon lens element 56 and is spread over a range of angles depicted by limit rays 72 to illuminate an angular field defined by the subtense of prisms 57-60 and lens 56 at the lamp filament 16. In this way there is 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 shape of the light source in order to meet the output beam requirements outlined above.

It is common for cycle light lamps to be of the 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 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 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 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

CLAIMS:

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 deterined 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 center.

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 centers 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 center.

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 fair 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, wherein the profile of the reflected beam from the light source has gaps in it where it pases through the lens and diverting means int he lens located int eh reflected beam gaps spreads incident direct light to the far field at angles beyond those where the reflector cuts off direct light.

11. A light according to claim 10, wherein the diverting means comprises an array of lenticular and/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 10, wherein the faces of the prismatic elements not struck by the incident direct light are frosted to minimise development of colored fringes in the far field.

15. A light according to claim 10, whrein 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.