Smooth headlight glass, in particular for a motor vehicle, and a method of manufacturing the reflector of such a headlight

The headlight comprises a light source, a reflector having a base surface that is selected to form images of the source in a determined distribution in a lighting direction that is axial and horizontal, and a closure glass. According to the invention, the closure glass is essentially free from deflecting stripes and the reflector includes, over at least a portion of its surface, a plurality of zones in which said base surface is replaced by substitution surfaces of outlines defined by projecting a plane array of polygonal zones onto the base surface, the plane array being defined as a function of a predetermined distribution of light flux. The array of zones corresponds to the array that would have been obtained if it had been an array of stripe zones formed on the closure glass, and the differential offset in a horizontal plane between the base surface and each substitution surface corresponds to the profile that the corresponding stripe would have had if it had been formed on the closure glass.

FIELD OF THE INVENTION 
The invention relates to a headlight, in particular a headlight for a motor 
vehicle. 
It relates in particular to a headlight of the type comprising a light 
source such as a filament lamp generally not having a cup, a reflector 
having a surface designed to form a determined distribution of images of 
the source in a lighting direction that is axial and horizontal, and a 
closure glass. In a non-limiting example, the surface of the reflector may 
be defined analytically so as to form images of the source such that all 
points thereof lie beneath a predetermined cutoff. 
BACKGROUND OF THE INVENTION 
Documents FR-A-2 536 502 and FR-A-2 536 503 describe headlights of that 
type, respectively defining a dipped beam and a fog beam essentially by 
the special shape of the reflector surface. 
That type of headlight makes it possible to avoid use not only of a cup or 
of a masking screen, but also to avoid a glass having high deflecting 
capability, and it thus provides a beam that is spread with good 
uniformity, particularly in the vertical direction. 
Nevertheless, those headlights, like conventional headlights, have until 
now required the use of a closure glass that is provided with deflecting 
zones (such as stripes or half-stripes), in particular to spread the beam 
in the horizontal direction and to make it more uniform. 
Under such circumstances, when the glass is considerably inclined, as may 
be desirable for styling reasons, it becomes difficult to implement such 
deflecting zones and their effectiveness decreases with increasing angle 
of inclination of the closure glass. 
OBJECTS AND SUMMARY OF THE INVENTION 
One of the objects of the invention is to provide a headlight enabling a 
standardized light beam to be produced which is made uniform solely by the 
reflector, so as to make it possible to use a glass that is smooth or that 
is provided with stripes that are not functional, i.e. that are purely 
decorative and that have no optical function. 
Essentially, to achieve this object, the invention provides for making the 
stripes directly on the reflector of the headlight, with the stripes being 
grouped together in zones as a function of the result to be achieved, said 
zones being defined in the same manner as the zones that are to be found 
on conventional deflecting headlight glasses. 
Patent GB-A-435 945 describes a headlight in which it is possible to omit 
deflecting stripes on the glass, which headlight is constituted by a stack 
of horizontal paraboloidal slices; each of the slices in the stack 
constituting an independent reflector that provides deflection of strictly 
parabolic type. 
The present invention provides a headlight, in particular for a motor 
vehicle, the headlight comprising: 
a light source; 
a reflector having a base surface that is suitable for forming a determined 
distribution of images of the source in a lighting direction that is axial 
and horizontal; and 
a closure glass, 
wherein: 
the closure glass is essentially free of deflecting stripes; and 
the reflector includes, over at least a portion of its surface, a plurality 
of zones in which said base surface is replaced by superimposition 
surfaces of outline defined by projecting a plane array of polygonal, and 
in particular rectangular, zones along said axial direction onto the base 
surface, the array being defined as a function of a predetermined 
distribution of light flux, said array of zones corresponding to the array 
that would have been obtained had it been an array of striped zones formed 
on the closure glass, and the differential offset in a horizontal plane 
between the base surface and the superimposition surface corresponding to 
the profile that said corresponding stripe would have had if it had been 
formed on the closure glass. 
The invention also provides a method of manufacturing a reflector for a 
headlight, in particular for a motor vehicle, the reflector being suitable 
for forming images of the source in a determined distribution, and the 
projector including a closure glass that is essentially free of deflecting 
stripes, the method comprising the following steps: 
defining a base reflecting surface for the reflector so as to form images 
of the source in a base distribution in a lighting direction that is axial 
and horizontal; 
replacing a plurality of zones of said base reflecting surface, over at 
least a portion thereof, with superimposition surfaces, the outlines of 
said superimposition surfaces being defined by projecting a plane array of 
polygonal, and in particular rectangular, zones onto the base surface 
along said axial direction, the array being defined as a function of a 
predetermined distribution of light flux, said array of zones 
corresponding to the array that would have been obtained if an array of 
stripe zones had been formed on the closure glass, and by selecting a 
differential offset in a horizontal plane between the base surface and the 
superimposition surface, which offset corresponds to the profile that the 
corresponding stripe would have had if it had been formed on the closure 
glass; 
making a mold for the reflector by machining as a function of data defining 
the base surface and the superimposition surfaces; and 
molding the reflector using said mold. 
The invention applies most advantageously to a reflecting surface that is 
analytically defined in such a manner as to form images of the source with 
all of the points thereof being situated beneath a predetermined cutoff. 
As appropriate, the superimposition surfaces may be such that two adjacent 
substitution surfaces are connected together either without any gap along 
their common edge, or else via a step along their common edge. 
According to another preferred aspect of the invention, over at least a 
major portion of the reflector, the superimposition surfaces are 
contiguous surfaces that connect to one another continuously in the 
horizontal direction along their common edges.

MORE DETAILED DESCRIPTION 
FIG. 1 is highly diagrammatic, showing a motor vehicle headlight that 
comprises a light source 10, in particular a filament lamp, a reflector or 
mirror 20 of the above-specified type having an analytically defined 
surface, and optionally truncated by two half-planes 21 and 22, and a 
closure glass 30. The light source 10 does not include any cup or masking 
screen, with the cutoff being defined solely by the shape of the reflector 
20. The assembly produces a light beam directed forwards from the vehicle 
in a lighting direction .DELTA. that is axial and horizontal. 
It may be observed that the filament can be replaced by the arc of a 
discharge lamp. 
In a manner characteristic of the invention, the closure glass 30 is 
essentially smooth or is provided with stripes that are decorative only, 
having no optical function, with the beam being spread out and made 
uniform in the horizontal direction solely by the reflector 20. 
To this end, an array of stripe zones is defined in a plane 40 that is 
perpendicular to the lighting direction .DELTA. as a function of the 
desired light distribution of the beam to be generated by the headlight, 
in exactly the same way as would have been used for defining such an array 
of stripe zones on a conventional deflecting closure glass extending 
perpendicularly to the lighting direction .DELTA.. 
The front view of FIG. 3 shows an array of deflecting zones corresponding 
to a first embodiment of the invention suitable for a left headlight 
mirror. These deflecting zones are referenced 41 and each of them may be 
contiguous or non-contiguous with other, adjacent zones. 
Each of the zones 41 is then projected along .DELTA. onto the surface 23 of 
the reflector 20, such that the lighting direction .DELTA. also 
constitutes the projection direction for this purpose. This has the effect 
of defining, for each zone 41, a corresponding zone 24 of curvilinear 
outline on the reflector (the zones 41 are themselves polygonal in 
outline), and a stripe-forming superimposition surface is formed at the 
location of each reflector zone 24, said superimposition surface 24 being 
defined relative to the projection surface 23 (i.e. the 
analytically-defined surface) by a differential offset .delta. in a 
horizontal plane and corresponding to the profile that the corresponding 
stripe would have had if it had been formed on a closure glass. 
The profile of the stripe can be seen, in particular, in FIG. 4 where the 
slightly curved shape exhibits a differential offset .delta. of 0.1 mm to 
0.5 mm in the direction normal to the projection surface 23. A greater 
offset could nevertheless be used if it is desired to impart a prismatic 
effect to the stripes. 
FIG. 4 shows complete stripes, i.e. adjacent surfaces 24 connect together 
without any gaps along their common edges 25. In a variant, instead of 
having complete stripes, it is possible to provide half-stripes, likewise 
oriented in an essentially vertical direction, but connected to one 
another via steps 26, as shown in FIG. 5, which steps do not impede proper 
operation given the essentially vertical orientation of the half-stripes. 
Any possible defects due to the discontinuities to which the steps give 
rise merely result in the corresponding light rays being deflected 
laterally. 
In a second embodiment, shown in FIG. 6 (and corresponding to a right 
headlight), "varying" stripes are used, i.e. the profile of each stripe 
varies continuously along its length, with the various zones 41 over the 
major portion of the reflector being contiguous areas that connect to one 
another continuously in the horizontal direction along their common edges. 
In the first embodiment, the discontinuities that result from the 
horizontal transition zones produce, in the light pattern, horizontal 
lines that can be dazzling, and which are also amplified if it is 
necessary to coat the mirror with a protective varnish since the varnish 
tends to be deposited non-uniformly and to concentrate in more or less 
unforeseeable manner around the discontinuities. This difficulty can be 
mitigated by using varying stripes.