Illumination – Modifier mountable on light source envelope
Reexamination Certificate
2002-05-29
2004-01-27
Husar, Stephen (Department: 2875)
Illumination
Modifier mountable on light source envelope
C362S307000, C362S308000, C362S310000, C362S328000, C362S329000
Reexamination Certificate
active
06682206
ABSTRACT:
The present invention relates to an illuminating spotlight emitting a narrow beam, comprising a highly concentrated light source and a concave reflector for emitting an illuminating beam in a given direction, along an axis of emission.
The invention relates also to a lighting installation produced using such a spotlight.
In order to control the distribution of the lighting in an area or more generally, at a site, it is in many cases valuable to have a beam of very precise angular definition. That means that the aperture angle of the beam must be very small.
In general, the beam is a luminous beam of rays that are in theory parallel, which beam is obtained by a parabolic reflector whose focal point corresponds to the light source of the bulb and whose axis is the axis of emission. Part of such a spotlight is shown in diagrammatic section in FIG.
1
.
However, the rays that are emitted do not form a totally parallel beam because the light source is neither a point source nor a monochromatic source.
Accordingly, only the beams that are emitted by the source located at the focal point F and strike the reflector represented by the segment of a parabola UP generating it are emitted in the form of relatively parallel rays. All the rays contained within the cone of axis X′X and of half-angle &dgr;o/2, of generating line FP passing the edge of the reflector, are emitted directly in the form of rays that are radial and not parallel to the axis X′X.
In practice, such a reflector is formed by a portion of a paraboloid of revolution of axis X′X, of focal point F and defined by its parameter p, its forward opening radius R
2
and its rearward opening radius R
1
(the rearward opening serves for the passage of the lamp). The flux used increases when the radius R
2
increases, and it is considered to be at its maximum when the characteristics of the reflector are such that:
p={square root over (R
1
*R
2
/2)}
The angle &ggr; of the captured flux is delimited by the contour UP of the reflector. The development of a more enveloping reflector would result in excessive dimensions. It must also be noted that the lamps have large dimensions relative to the reflector, and the real focal point necessarily extends beyond the theoretical focal point, which is the main cause of the lack of parallelism mentioned above. The divergence increases with the dimensions of the source or vice versa, if the focal distance diminishes and the diameter of the reflector diminishes relative to that of the source. The positioning of a lens in front of the opening face of the reflector might be considered, but it would correct not only the direct flux but also the flux of parallel rays reflected by the reflector.
In conclusion, the correction provided by a lens positioned at the front would not be very effective.
Finally, it must be noted that the effective angle of emission of a beam is very much greater than the angle attributed to, a light source equipped with a reflector, such as, for example, halogen bulbs equipped directly with a reflector. That angle is defined as being the angle of emission of 50% of the luminous flux, the remainder of the flux being emitted in directions that are not contained within that cone of emission. The definition of the angle of illumination appears in
FIG. 1A
, which shows the separation graph of the luminous intensity as a function of the angle relative to the axis X′X (
FIG. 1
) That distribution is a bell curve, and the angle of the spotlight is the angle giving, by definition, the intensity greater than the half-average IM/2 relative to the maximum intensity IM in the direction of the axis (&agr;=o). The angle &agr; attributed to the beam is thus obtained, in which angle the flux should be the maximum.
In practice, that means that the beam is not very precise at all.
The object of the present invention is to develop a spotlight allowing the emission of a beam that has a very small angle and that groups together almost all of the luminous flux emitted by the source.
To that end, the invention relates to a spotlight of the type defined above, characterised by
a convergent lens positioned between the source and the reflector,
in a plane passing through the axis of emission,
the concave reflector formed by a conic section (ellipse or parabola),
the source is bordered laterally on the side of the reflector by a sector of the convergent lens giving a virtual image of the source, which virtual image is situated beyond the axis of emission, on the other side from the lens,
the virtual image of the light source being formed at the focal point of the conic section locally defining the reflector.
In an advantageous manner, the reflector comprises a body of revolution about the axis of emission XX. According to the circumstances, the conic is a parabola whose axis is parallel to the axis of emission.
Thanks to the displacement of the light source by its virtual image, it is possible to have a sector of a parabola of relatively large focal distance, that is to say a highly enveloping sector of a parabola.
It receives all the luminous flux transmitted by the peripheral lens. Since the lens is itself highly enveloping, a large fraction of the emitted flux thus passes through the lens to be reflected, by the reflector, in the form of rays that are almost parallel.
Only the light rays emitted within the solid angle represented by the source and the rear edge of the lens are directed to the rear without being recovered. In general, those rays avoid the optical system formed by the peripheral lens and have a random orientation. The corresponding, frontal part for the solid angle defined by the frontal edge of the peripheral lens, and the vertex of which is the light source, is emitted directly.
According to an advantageous feature, the forward opening of the peripheral lens is occupied by a lens whose focal point corresponds to the light source, so that that lens emits a beam of rays that are parallel to the axis of emission XX. That luminous flux is added to the luminous flux returned by the reflector.
In that manner, almost all of the luminous flux of the source is recovered in the form of a beam of parallel rays, that is to say, in practice, of rays that are very slightly divergent. The solid angles of emission &ggr; and &dgr; are totally controlled. Only the rear angle of emission &bgr; corresponds to flux of which a portion will be absorbed.
In an advantageous manner, the peripheral lens and the frontal lens are produced in a single piece or constitute a single piece by the assembly of two lenses produced separately. The reflector is preferably made of glossy polished aluminium or of vacuum metallised plastics material, or of glass with reflective dichroic metallisation with, for example, titanium oxide.
According to another feature of the invention, the reflector is generated by an arc of an ellipse whose second focal point is located on the axis of emission.
The invention relates also to a lighting installation composed of a spotlight as defined above and of at least one mirror forming a lighting system having an offset focal point, for illuminating an area for illumination that the spotlight cannot reach directly.
Under such conditions, the spotlight can be installed in a location that is readily accessible; that area can also be accessible on account of the power supply that exists in the location or that is easily brought to the location, without requiring the complex installation in certain cases of cables such as for illumination with a direct spotlight.
Thanks to the very precise pencil of rays formed by the spotlight, it is simple to aim at a deflection mirror, even such a mirror located at a relatively great distance from the spotlight, without giving rise to the considerable loss of luminous flux passing to the side of the mirror or without requiring a large-sized returning mirror. On the contrary, it is possible to use mirrors which are small in size, are light-weight and are simple to produce and install.
Since the mirror is generally turned wi
Drinker Biddle & Reath LLP
FD Eclairage
Husar Stephen
LandOfFree
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