Patent Description:
Distribution of light produced by a light source can be important or even critical in some applications. The light source may comprise, for example but not necessarily, one or more light emitting diodes "LED", one or more filament lamps, or one or more gas-discharge lamps. The distribution of light produced by a light source can be modified with optical devices such as lenses, reflectors, and combined lens-reflector devices that comprise sections which act as lenses and sections which act as reflectors. <FIG> show isometric views of an exemplifying optical device <NUM> according to the prior art for modifying light distribution. The optical device <NUM> is made of suitable transparent material whose refractive index is greater than one. <FIG> shows a view of a section taken along a line A-A shown in <FIG>. The section plane is parallel with the yz-plane of a coordinate system <NUM>. Furthermore, <FIG> shows a polar-plot illustrating a light distribution pattern produced by a light source <NUM> and the optical device <NUM>. In the exemplifying situation shown in <FIG>, the geometric optical axis <NUM> of the optical device <NUM> is parallel with the z-axis of the coordinate system <NUM>. The optical device <NUM> comprises a center section <NUM> that comprises a lens portion <NUM> for modifying the distribution of a first part of the light emitted by the light source <NUM>. The optical device <NUM> comprises a peripheral section <NUM> surrounding the center section <NUM> and comprising a conical surface <NUM>. The conical surface <NUM> acts as a reflector surface so that total internal reflection "TIR" takes place when a light beam arrives from the light source <NUM> at a conical surface <NUM>. In <FIG>, exemplifying light beams belonging to the first part of the light are depicted with arrow-headed dashed lines and exemplifying light beams belonging to the second part of the light are depicted with arrow-headed dash-and-dot lines.

As illustrated by the polar-plot shown in <FIG>, the intensity of light decreases rapidly when an absolute value of an angle with respect to the geometric optical axis <NUM> of the optical device <NUM> exceeds about <NUM> degrees. As a corollary, areas such as a corner area <NUM> illustrated in <FIG> may remain insufficiently illuminated when the optical device <NUM> is mounted on a ceiling. It is possible to spread the light distribution pattern by increasing the cone angle of the conical surface <NUM> and by shaping the lens portion <NUM> to be less collimating. However, in many cases there is a need to keep the whole light distribution pattern within desired limits. For example, the light distribution pattern illustrated by the polar-plot shown in <FIG> is between about -<NUM> and +<NUM> degrees with respect to the geometric optical axis <NUM> of the optical device <NUM>. Thus, in many cases, there is a need to increase the intensity of light in fringe areas of the light distribution pattern.

An optical device according to the prior art is disclosed in the document <CIT>.

The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments.

In this document, the word "geometric" when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional.

In accordance with the invention, there is provided a new optical device for modifying distribution of light produced by a light source.

An optical device according to the invention is made of transparent material and the optical device comprises:.

The conical surface comprises ridges in which total internal reflection "TIR" takes place when a light beam arrives from the light source at one of side surfaces of each ridge, and surface penetration takes place when the reflected light beam arrives at the other one of the side surfaces of the ridge under consideration. Thus, the conical surface acts both as a reflective surface and as a refractive surface for achieving a desired light distribution pattern so that, when compared to the light distribution pattern shown in <FIG>, more light can be directed to the fringe areas of the light distribution pattern. The conical surface intersects a geometric plane perpendicular to the geometric optical axis along a closed path having a cogged shape.

In this document, the wording "conical surface" is not limited to cases where geometric section curves between the conical surface and geometric planes perpendicular to the above-mentioned geometric optical axis are circles. In an optical device according to the invention, the geometric section curves have a non-circular shape.

In accordance with the invention, there is provided also a new illumination device that comprises:.

The light source may comprise, for example, one or more light emitting diodes "LED".

In accordance with the invention, there is provided also a new mold having a form suitable for manufacturing, by mold casting, a piece of transparent material, e.g. plastic, having a shape of an optical device according to the invention.

Various exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims.

Exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in conjunction with the accompanying drawings.

The exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below with reference to the accompanying drawings, in which:.

<FIG> show isometric views of an optical device <NUM> according to an exemplifying and non-limiting embodiment of the invention. <FIG> shows a view of a section taken along a line A-A shown in <FIG>. The section plane is parallel with the yz-plane of a coordinate system <NUM>. Furthermore, <FIG> shows a polar-plot illustrating a light distribution pattern produced by a light source <NUM> and the optical device <NUM>. The light source <NUM> may comprise for example one or more light emitting diodes "LED", one or more filament lamps, or one or more gas-discharge lamps. In the exemplifying situation shown in <FIG>, the geometric optical axis <NUM> of the optical device <NUM> is parallel with the z-axis of the coordinate system <NUM>. The optical device <NUM> is made of transparent material whose refractive index is greater than one. The transparent material can be for example acrylic plastic, polycarbonate, optical silicone, or glass. The method of manufacture of the optical device <NUM> can be for example mold casting.

The optical device <NUM> comprises a center section <NUM> that comprises a lens portion <NUM> for modifying the distribution of a first part of the light emitted by the light source <NUM>. In this exemplifying case, a light egress surface of the lens portion <NUM> is convex and a light ingress surface of the lens portion <NUM> comprises a concave center part and a flat part surrounding the concave center part. The optical device <NUM> comprises a peripheral section <NUM> surrounding the center section <NUM> and comprising a conical surface <NUM> for modifying distribution of a second part of the light emitted by the light source. In <FIG>, exemplifying light beams belonging to the first part of the light are depicted with arrow-headed dashed lines and exemplifying light beams belonging to the second part of the light are depicted with arrow-headed dash-and-dot lines. The optical device <NUM> and the light source <NUM> constitute an illumination device according to an exemplifying and non-limiting embodiment of the invention. The light source <NUM> is mechanically supported so that the light source <NUM> is located substantially symmetrically with respect to the geometric optical axis <NUM> of the optical device. Mechanical support structures for supporting the light source <NUM> are not shown in <FIG>.

As illustrated in <FIG>, the above-mentioned conical surface <NUM> comprises ridges. In <FIG>, one of the ridges is denoted with a reference <NUM>. The ridges are oriented so that the ridges are perpendicular to the circumferential direction of the conical surface. <FIG> shows a section view of the ridge <NUM> so that the section plane is parallel with the xy-plane of the coordinate system <NUM>. As illustrated in <FIG>, the ridge <NUM> is shaped so that total internal reflection "TIR" takes place when a light beam arrives from the light source at one of side surfaces 207a and 207b of the ridge <NUM>, and surface penetration takes place when the reflected light beam arrives at the other one of the side surfaces. Thus, the conical surface <NUM> having the ridges acts both as a reflective surface and as a refractive surface for achieving the light distribution pattern shown by the polar-plot of <FIG>. By comparing the polar-plot of <FIG> to the polar-plot of <FIG>, one can see that the light distribution pattern obtained with the optical device <NUM> according to the embodiment of the invention and the light distribution pattern obtained with the optical device <NUM> according to the prior art are both between about -<NUM> and +<NUM> degrees with respect to the geometric optical axis, but the optical device <NUM> according to the embodiment of the invention directs more light to the fringe areas of the light distribution pattern.

In the exemplifying optical device <NUM> illustrated in <FIG>, the center section <NUM> is substantially rotationally symmetric with respect to the geometric optical axis <NUM> and tops of the ridges of the conical surface <NUM> touch, as tangents, to a geometric conical surface substantially rotationally symmetric with respect to the geometric optical axis <NUM>. A dashed line <NUM> in <FIG> represents a part of a geometric section curve between the above-mentioned geometric conical surface and the section plane related to <FIG>. The section plane is parallel with the xy-plane of the coordinate system <NUM>. The cone angle of the above-mentioned geometric conical surface can be for example in the range from <NUM> degrees to <NUM> degrees. In <FIG>, the cone angle is denoted as γ. It is, however, also possible that an optical device according to an embodiment of the invention has an elongated shape so that the optical device is suitable for an elongated light source such as e.g. a fluorescent tube.

In the exemplifying optical device <NUM> illustrated in <FIG>, the cross-sections of the ridges are substantially V-shaped as illustrated in <FIG>. The angle α between the side surfaces of each ridge is advantageously in the range from <NUM> degrees to <NUM> degrees, e.g. about <NUM> degrees, so as to achieve the functionality where a light beam arriving from the light source is reflected by total internal reflection on a side surface of a ridge and the reflected light beam penetrates the other side surface of the ridge. It is, however, also possible that an optical device according to an embodiment of the invention has ridges with curved, i.e. non-planar, side surfaces.

The exemplifying optical device <NUM> illustrated in <FIG> comprises a flange section <NUM> for mechanically supporting the center section <NUM> and the peripheral section <NUM>. As shown in <FIG>, the flange section <NUM> is, in the direction of the geometric optical axis <NUM>, between the conical surface <NUM> and a light egress surface of the lens portion <NUM>. It is worth noting that the flange section <NUM> is a mechanical support structure and different mechanical support structures are possible in optical devices according to different embodiments of the invention. For example, instead of the flange section <NUM> shown in <FIG>, there can be isthmuses for supporting the center section <NUM> and the peripheral section <NUM>. For another example, an optical device according to an embodiment of the invention may comprise a mechanical support section connected to the light ingress-side of the lens portion.

In an optical device according to an exemplifying and non-limiting embodiment of the invention, the light ingress surface of the lens portion <NUM> is a color mixing surface so that it comprises converging and diverging portions located alternately with respect each other. In a color mixing surface, light beams exhibiting different wavelengths are effectively mixed thus producing a light pattern which contains all wavelengths evenly distributed across the pattern. Thus, the color mixing surface mixes light beams representing different colors, i.e. different wavelengths, resulting from possible nonidealities of a light source.

Claim 1:
An optical device (<NUM>) for modifying light distribution, the optical device being made of transparent material and comprising:
- a center section (<NUM>) comprising a lens portion (<NUM>) for modifying distribution of a first part of light emitted by a light source when the light source is located symmetrically with respect to a geometric optical axis (<NUM>) of the optical device, and
- a peripheral section (<NUM>) surrounding the center section and comprising a conical surface (<NUM>) for modifying distribution of a second part of the light emitted by the light source,
wherein the conical surface comprises ridges (<NUM>), the conical surface intersecting a geometric plane perpendicular to the geometric optical axis (<NUM>) of the optical device along a closed path having a cogged shape, characterized in that total internal reflection takes place in said ridges when a light beam arrives, from the light source, at one of side surfaces of each ridge, and surface penetration takes place when the reflected light beam arrives at another one of the side surfaces of the ridge under consideration.