Light guide

A light guide (201) including a transparent element is presented. The transparent element includes a first end (203) including a place for a light source, a second end (204) opposite the first end, an outer surface (205) between the first and second ends, and an interior channel (206) extending from the first end to the second end. The interior channel includes a first portion (207) beginning from the first end and a second portion (208) extending to the second end. The first portion is shaped to guide at least part of light falling to its wall into the transparent material and the outer surface provides total reflection for reflecting the light towards the second end. The second portion is shaped so that light passed through the first portion without falling to a wall of the first portion reaches the second end without falling to a wall of the second portion.

FIELD OF THE INVENTION

The invention relates generally to illuminating engineering. More particularly, the invention relates to a light guide for modifying a light distribution pattern of a light source that can be, for example but not necessarily, a light emitting diode “LED”.

BACKGROUND

Distribution of light produced by a light source can be important or even critical in some applications. The light source can be, for example but not necessarily, a light emitting diode “LED”, a filament lamp, or a gas-discharge lamp.FIG. 1ashows a view of a section taken from an exemplifying light guide101according to the prior art for modifying a light distribution pattern of a light source102. Some of the light beams radiated by the light source102are depicted with dashed line arrows inFIG. 1a. The light guide101can be rotationally symmetric with respect to a geometric line120shown inFIG. 1a. The geometric line120is parallel with the z-axis of a coordinate system199. The light guide101is made of transparent material having refractive index greater than unity. The light guide comprises a first end103comprising a place for the light source, a second end104opposite the first end, and an outer surface105between the first and second ends. The outer surface105is shaped to provide total reflection for reflecting light towards the second end104. An inconvenience related to light guides of the kind described above is that also light that is not reflected by the outer surface105is attenuated by the transparent material.FIG. 1bshows a view of a section taken from another exemplifying light guide111according to the prior art for modifying a light distribution pattern of a light source112. Some of the light beams radiated by the light source112are depicted with dashed line arrows inFIG. 1b. The light guide111can be rotationally symmetric with respect to a geometric line121shown inFIG. 1b. The light guide111is a bowl-like element having a first end113comprising a place for the light source112, a second end114opposite the first end, and a reflective layer115on the inner surface of the bowl-like element. In this case, light is not attenuated by any transparent material, but an inconvenience related to the light guide illustrated inFIG. 1bis the need for the reflective layer115on the inner surface of the bowl-like element.

SUMMARY

In accordance with the invention, there is provided a new light guide for modifying the light distribution pattern of a light source. A light guide according to the invention comprises a transparent element made of transparent material having refractive index greater than unity, the transparent element comprising:a first end comprising a place for the light source,a second end opposite the first end,an outer surface between the first and second ends, andan interior channel free from the transparent material and extending from the first end to the second end.

The interior channel comprises a first portion beginning from the first end and a second portion extending to the second end. The first portion is shaped to guide at least part of light falling to a wall of the first portion into the transparent material and towards the outer surface, and the outer surface is shaped to provide total reflection for reflecting the at least part of the light towards the second end. The second portion of the interior channel is at least as long as the first portion, and the second portion is shaped so that:
W/L≧W1/L1, whenL≧L1,  (1)
where L is a distance from the first end, W is a width of the interior channel at the distance L from the first end, L1is a length of the first portion, and W1is a width of the first portion at a distance of L1from the first end.

As the lower limit of the width of the second portion increases according to the equation (1) when the distance L from the first end increases, i.e. the distance from the light source increases, light that has passed through the first portion without falling to the wall of the first portion reaches the second end without falling to the wall of the second portion. Therefore, the light that has passed through the first portion without falling to the wall of the first portion is not subject to attenuation caused by the transparent material. On the other hand, the total reflection provided by the above-mentioned outer surface can be utilized.

In accordance with the invention, there is provided also a new light guide system comprising a light guide according to the invention and a collimating lens for collimating light coming from the second end of the light guide.

In accordance with the invention, there is provided also a new illuminator device comprising at least one light source and at least one light guide according to the invention. The at least one light source may comprise, for example, one or more light emitting diodes “LED”.

A light guide according to an exemplifying and non-limiting embodiment of the invention is a single piece of transparent material that can be manufactured, for example, by mold casting. In accordance with the invention, there is provided also a new mold having a form suitable for manufacturing, by mold casting, the above-mentioned single piece of the transparent material.

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

Various 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 connection with the accompanying drawings.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

FIGS. 1aand1bhave already been explained in the Background-section of this document.

DESCRIPTION OF EXEMPLIFYING EMBODIMENTS

FIG. 2shows a section view of a light guide201according to an exemplifying embodiment of the invention for modifying the light distribution pattern of a light source202that can be, for example but not necessarily, a light emitting diode “LED”, a filament lamp, or a gas-discharge lamp. The section shown inFIG. 2has been taken along a section plane parallel to xz-plane of a coordinate system299. The light guide comprises a transparent element215made of solid transparent material having the refractive index greater than unity. The transparent material can be, for example, acrylic plastic, polycarbonate, optical silicone, or glass. The method of manufacture of the transparent element215can be for example mold casting. The transparent element comprises a first end203comprising a place for the light source202, a second end204opposite the first end, an outer surface205between the first and second ends, and an interior channel206that is free from the transparent material and extends from the first end to the second end as illustrated inFIG. 2. The interior channel206comprises a first portion207beginning from the first end203and a second portion208extending to the second end204. The first portion is shaped to guide at least part of light falling to a wall of the first portion into the transparent material and towards the outer surface205. Therefore, the wall of the first portion207of the interior channel operates as a light collector. The outer surface205is shaped to provide total reflection for reflecting the at least part of the light towards the second end204. InFIG. 2, some of the light beams falling to the wall of the first portion207of the interior channel and reflected by the outer surface205are depicted with dashed line arrows.

The second portion208of the interior channel206is at least as long as the first portion207, and the second portion is shaped so that:
W/L≧W1/L1, whenL≧L1,
where L is a distance from the first end, W is the width of the interior channel at the distance L from the first end, L1is the length of the first portion, and W1is the width of the first portion at the distance of L1from the first end. The length L1of the first portion207can be defined with the aid of a straight line that begins from the light source202and touches the wall of the interior channel without penetrating the wall of the interior channel. A point of contact209between the straight line and the wall of the interior channel determines the length L1of the first portion207as illustrated inFIG. 2. As can be seen fromFIG. 2, the light that has passed through the first portion207without falling to the wall of the first portion reaches the second end204without falling to the wall of the second portion208. InFIG. 2, some of the light beams passing through the first portion207without falling to the wall of the first portion are depicted with dot-and-dash line arrows. The interior channel206is advantageously symmetric with respect to a geometric line220that is parallel with the distance between the first and second ends.

FIGS. 3aand3billustrate a light guide301according to an exemplifying embodiment of the invention.FIG. 3bshows a view of a section taken along the line A-A shown inFIG. 3a. In this exemplifying case, the transparent element315of the light guide301is substantially rotationally symmetric with respect to a geometric center line320of the interior channel, where the geometric center line is parallel with the distance L2between the first and second ends of the transparent element315. InFIG. 3, the geometric center line is parallel with the z-axis of a coordinate system399.

In the exemplifying light guide illustrated inFIGS. 3aand3b, the wall of the second portion308of the interior channel306defines a truncated cone opening towards the second end304. The wall of the first portion307of the interior channel defines another truncated cone opening towards the second end and having a coning angle φ1smaller than the coning angle φ2of the truncated cone defined by the wall of the second portion308.

An illumination device according to an exemplifying embodiment of the invention comprises the light guide301and a light source302. The light source302is substantially a point-form light source that can be, for example, a light emitting diode “LED”.

FIG. 3cshows a section view of a light guide according to an exemplifying embodiment of the invention. The transparent element315of the light guide is substantially rotationally symmetric with respect to a geometric center line320of the interior channel306. The wall of the second portion308of the interior channel306defines a truncated cone opening towards the second end304and having a coning angle θ2. The wall of the first portion307of the interior channel defines another truncated cone opening towards the first end303and having a coning angle θ1.

FIG. 3dshows a section view of a light guide according to an exemplifying embodiment of the invention. The transparent element315of the light guide is substantially rotationally symmetric with respect to a geometric center line320of the interior channel306. In this exemplifying case, the interior channel306has a beveling325at its first end303as illustrated inFIG. 3d.

FIGS. 4aand4billustrate a light guide401according to an exemplifying embodiment of the invention for modifying the light distribution pattern of a light source402.FIG. 4bshows a view of a section taken along the line A1-A1shown inFIG. 4a, a view of a section taken along the line A2-A2shown inFIG. 4a, and a view of a section taken along the line A3-A3shown inFIG. 4a. In this exemplifying case, the transparent element415of the light guide401has a form having a substantially constant cross-section taken along a geometric section plane moving a predetermined displacement in a direction that is perpendicular to the geometric section plane, perpendicular to a distance L2between the first and second ends, and perpendicular to the width W of the interior channel. The above-described geometrical property is manifested by the fact that the section views shown inFIG. 4bare similar to each other. The above-mentioned geometric section plane is parallel with the xz-plane of a coordinate system499and it moves in a direction parallel with the y-axis of the coordinate system499.

An illumination device according to an exemplifying embodiment of the invention comprises the light guide401and the light source402. The light source402is substantially a line-form light source that can be, for example, a fluorescence tube or a plurality of light emitting diodes “LED” in line.

FIG. 5shows a section view of a light guide501according to an exemplifying embodiment of the invention for modifying the light distribution pattern of a light source502. The light guide comprises a transparent element515made of solid transparent material having the refractive index greater than unity. The transparent element comprises a first end503comprising a place for the light source502, a second end504opposite the first end, an outer surface505between the first and second ends, and an interior channel506that is free from the transparent material and extends from the first end to the second end as illustrated inFIG. 5. The interior channel506comprises a first portion507beginning from the first end and a second portion508extending to the second end. The first portion is shaped to guide at least part of light falling to a wall of the first portion into the transparent material and towards the outer surface505. The outer surface is shaped to provide total reflection for reflecting the at least part of the light towards the second end504. InFIG. 5, some of the light beams falling to the wall of the first portion507of the interior channel and reflected by the outer surface505are depicted with dashed line arrows. The second portion508of the interior channel506is at least as long as the first portion507, and the second portion is shaped so that W/L>W1/L1when L>L1, where L is the distance from the first end, W is the width of the interior channel at the distance L from the first end, L1is the length of the first portion, and W1is the width of the first portion at the distance of L1from the first end. In the exemplifying case illustrated inFIG. 5, the interior channel comprises a step-wise widening510in the transitional region from the first portion507to the second portion508. The exemplifying case illustrated inFIG. 5, shows that the rule W/L≦W1/L1gives only a lower limit for the width W of the interior channel506at the distance L from the first end503. InFIG. 5, some of the light beams passing through the first portion507without falling to the wall of the first portion are depicted with dot-and-dash line arrows.

FIG. 6ashows a section view of a light guide601according to an exemplifying embodiment of the invention for modifying the light distribution pattern of a light source602. In this exemplifying case, the interior channel606is shaped to be smooth so that there is no clearly visible turning point in the profile of the interior channel606on the transitional region from the first portion607to the second portion608. Also in this case, the length L1of the first portion607can be defined with the aid of a straight line that begins from the light source602and touches the wall of the interior channel606without penetrating the wall of the interior channel. A point of contact609between the straight line and the wall of the interior channel determines the length L1of the first portion607as illustrated inFIG. 6a. As can be seen fromFIG. 6a, the light that has passed through the first portion607without falling to the wall of the first portion reaches the second end604without falling to the wall of the second portion608.

FIG. 6bshows a section view of a light guide according to an exemplifying embodiment of the invention for modifying the light distribution pattern of a light source. In this exemplifying case, the wall626of the second portion608of the interior channel606is staggered so that part of light reflected from the first surface605penetrates the wall626and another part of this light is reflected from the wall626towards the second end604of the interior channel606. Some of the light beams reflected from the surface605are depicted with dashed line arrows inFIG. 6b. It is also possible that the wall626of the second portion608is shaped so that it reflects most of the light falling to it, or so that most of the light penetrates the wall626and the wall acts as a refracting surface.

FIG. 7shows a section view of a light guide system according to an exemplifying embodiment of the invention for modifying the light distribution pattern of a light source702. The light guide system comprises a light guide701according to an exemplifying embodiment of the invention and a collimating lens718for collimating the light coming from the light guide701.

FIGS. 8aand8billustrate an illuminator device according to an exemplifying embodiment of the invention.FIG. 8bshows a view of a section taken along the line A-A shown inFIG. 8a. The illuminator device comprises light sources802a,802band802c, and light guides801a,801band801c. Each of the light guides is according to an embodiment of the invention. Each of the light sources802a-802cmay comprise at least one light emitting diode “LED”. In the exemplifying case illustrated inFIGS. 8aand8b, the light guides801a-801care parts of a single piece819of transparent material.

The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. In the above-presented examples, the light guide comprises only transparent material. However, in some cases, the light guide may comprise also parts made of non-transparent material such as, for example, parts for providing mechanical support to the light source.