WO2010067282A1

WO2010067282A1 - Lighting apparatus

Info

Publication number: WO2010067282A1
Application number: PCT/IB2009/055501
Authority: WO
Inventors: Rifat A. M. Hikmet
Original assignee: Koninklijke Philips Electronics N. V.
Priority date: 2008-12-12
Filing date: 2009-12-04
Publication date: 2010-06-17

Abstract

A lighting apparatus (1) is presented, wherein the lighting apparatus (1) comprises a laser (2) for emitting a first laser beam (3) and a subdividing and redirection element (4) for generating second laser beams (6) by refraction or reflection. At least two of the second laser beams (6) propagate at least in part in different directions and would therefore be imaged at different locations on a retina of a human eye, wherein the intensity at each of these locations on the retina is reduced in comparison to a corresponding intensity of an image on the retina caused directly by the first laser beam (3), thereby improving or generating eye safety, while the efficiency of the lighting apparatus (1) is still high because the second laser beams (6) are generated by refraction or reflection.

Description

LIGHTING APPARATUS

FIELD OF THE INVENTION

The invention relates to a lighting apparatus and a lighting method.

BACKGROUND OF THE INVENTION

US 2007/0109784 Al discloses a lighting apparatus comprising a laser emitting a laser beam being expanded by a negative lens and collimated by a positive lens. The expanded collimated light beam is directed onto a holographic diffuser to produce a diffused light beam. The diffused light beam has an expanded cross-section and provides an extended glare source at increased power downrange. The extended source produced by the holographic diffuser creates an extended image on the retina of the human eye. The extended retinal image permits a higher power laser exposure, compared to a point source image common in conventional designs.

This lighting apparatus has the drawback that the holographic diffuser has a low efficiency due to back reflection and low transmission. Furthermore, the efficiency of the holographic diffuser depends on the collimation of the laser beam traversing the holographic diffuser. If the laser beam is not well collimated, the efficiency of the holographic diffuser is further reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a lighting apparatus and a lighting method comprising a laser, wherein the eye safety of laser light is improved or generated with an improved efficiency.

In a first aspect of the present invention a lighting apparatus is presented, wherein the lighting apparatus comprises a laser for emitting a first laser beam and a subdividing and redirection element comprising several subdividing and redirection regions, wherein the subdividing and redirection regions are adapted such that, if the first laser beam illuminates several of the subdividing and redirection regions, from each of these illuminated subdividing and redirection regions a second laser beam originates by refraction or reflection, wherein at least two second laser beams propagate at least in part in different directions.

The expression "wherein at least two second laser beams propagate at least in part in different directions" means that at least a part of one of the at least two second laser beams and at least a part of another of the at least two second laser beams propagate in different directions. In particular, at least two second laser beams propagate entirely in different directions.

Since the several illuminated subdividing and redirection regions generate several second laser beams, wherein at least two of the second laser beams propagate at least in part in different directions, the at least two second laser beams would be imaged at different locations on a retina of a human eye, wherein the intensity at each of these locations on the retina is reduced in comparison to a corresponding intensity of an image on the retina caused directly by the first laser beam. Thus, since the second laser beams are still laser beams, eye safety can be improved or can be generated, wherein the used light is still laser light. In particular, by subdividing the first laser beam into several second laser beams the intensity on the retina can be reduced by orders of magnitude, while the subdividing and redirection regions can be adapted such that a cross-section of a bundle of several second laser beams can be kept small and the collimation of this bundle, i.e. the overall collimation of the second laser beams, can still be high. Furthermore, since a holographic diffuser is not used by the lighting apparatus for generating the second laser beams, but subdividing and redirection regions, which refract or reflect at least two second laser beams at least in part in different directions, the adverse effects of using a holographic diffuser, i.e. of using a diffractive element, are eliminated, in particular, the efficiency, which can be defined in the prior art as the ratio of the light illuminating the holographic diffuser to the light that has passed the holographic diffuser or in the present invention as the ratio of the light illuminating the subdividing and redirection element to the light that has passed the subdividing and redirection element, is increased. Therefore, eye safety of the laser light is improved or generated with an improved efficiency of the lighting apparatus.

Furthermore, holographic diffusers as used in the prior art have a

Gaussian intensity distribution as a function of angle, which is for example defined as the angle between a ray of the diffused light to the normal of the diffuser surface, at the position, where the respective ray originates from the diffuser, thereby distorting the initial intensity profile of the laser. In contrast, the second laser beams originate from the subdividing and redirection regions by refraction or reflection, wherein by using refraction or reflection the intensity profile of the first laser beam is not modified or a desired intensity distribution and/or shape can be produced while maintaining high efficiency.

It is further preferred that the subdividing and redirection regions are adapted such that the second laser beams form a third laser beam. The second laser beams preferentially overlap and/or meet each other while propagating and form the third laser beam.

The subdividing and redirection regions can be adapted such that not all second laser beams are directed in different directions. In another embodiment, the subdividing and redirection regions can be adapted such that all second laser beams are directed in different directions.

The subdividing and redirection regions can be adapted such that they refract or reflect the first beam such that rays of a second laser beam propagate in different directions. In an embodiment the rays of a second laser beam can be traced to a point, e.g. i.e. to a focal point of a negative or positive lens or of a concave or convex mirror.

The subdividing and redirection regions subdivide the first laser beam into the second laser beams and redirect the second laser beams, in particular substantially, by refraction or reflection, wherein diffraction is preferentially substantially avoided. This means that preferentially the subdivision and redirection is mainly or completely effected by refraction or reflection. It is further preferred that a diffraction is not present or that an influence of diffraction on the subdivision and the redirection is neglectable small. It should be noted that the term "by refraction or reflection" does not relate to an exclusive "or", i.e. the second laser beams can be generated by refraction only, by reflection only or by refraction and reflection.

It is preferred that the lighting apparatus is adapted to expand the first laser beam before meeting the subdividing and redirection element such that the several subdividing and redirection regions are illuminatable. The first laser beam is preferentially expanded such that the cross-section of the first laser beam at the subdividing and redirection element is increased.

The lighting apparatus is preferentially adapted such that the cross-section of the first laser beam is expanded such that several of the subdividing and redirection regions are within this cross-section, if the expanded first laser beam is directed onto the subdividing and redirection element. The subdividing and redirection regions are preferentially arranged such that different subdividing and redirection regions are met by the first laser beam at different parts of the expanded cross-section of the first laser beam.

In an embodiment, the lighting apparatus comprises a beam expanding unit for expanding the first laser beam. If the first laser beam is divergent, the expansion of the first laser beam is not necessarily achieved by a beam expanding unit, because the expansion can be obtained by choosing an appropriate distance between the laser and the subdividing and redirection element.

It is further preferred that the subdividing and redirection regions are adapted to direct the second laser beams such that the divergence of the first laser beam is different, in particular smaller, than the divergence of a third laser beam formed by the second laser beams. Thus, a bundle of the second laser beams forms a third laser beam having a divergence different, in particular smaller, than the divergence of the first laser beam. In an embodiment, the first laser beam is a parallel beam, wherein the divergence of the third laser beam formed by the bundle of the second laser beams is larger than the divergence of the first laser beam. Furthermore, in this embodiment, a lens is provided behind the subdividing and redirection element, and the subdividing and redirection regions and/or the lens are adapted to send the third laser beam such that the lens totally collects the third laser beam. In this way an eye safe light beam is produced in an efficient way, i.e. with almost no light loss. The lens can be positioned such that the third laser beam is collimated. It is further preferred that at least some of the subdividing and redirection regions are adapted to increase the divergence of the individual second laser beams in comparison to the divergence of the first laser beam. In an embodiment, the subdividing and redirection element comprises a lens array, in particular, a micro lens array, defining the subdividing and redirection regions, wherein the first laser beam is parallel and travels through the lens array and wherein each individual lens is adapted such that the divergence of the respective second laser beam is larger than the divergence of the first laser beam. Furthermore, in this embodiment, a lens is placed behind the subdividing and redirection element and the subdividing and redirection element is adapted such that the second laser beams are totally collected by the lens. In this way, in an efficient way with almost no light loss an eye safe light source can be obtained, wherein the lens can be located such that a bundle of the second laser beams forming a third laser beam is collimated.

The laser is for example a laser diode.

In a preferred embodiment, the lighting apparatus is adapted such that the intensity on a retina of a healthy human eye of each of the several second laser beams is below a predefined threshold related to eye safety, if the second laser beams are directed to the healthy human eye. This intensity caused by a second laser beam could also be regarded as a local intensity. In particular, the predefined threshold is equal to or smaller than 10³ Wcm^~2 . It is further preferred that the predefined threshold is equal to or smaller than 10² Wcm^~2. The local intensity should be below the predefined threshold for each of the several second laser beams independent of how the second laser beams are directed to the healthy human eye, i.e. even if the second laser beams are directed to the healthy human eye such that a maximal local intensity, which is achievable with the lighting apparatus, is reached, this maximal achievable local intensity on the retina is below the predefined threshold.

A healthy human eye is a human eye having an eye lens focusing a parallel beam onto the retina.

If it is assumed that the healthy human eye can still reasonably focus at a distance of 25 cm with a fully open iris with a diameter of 8 mm, the healthy human eye can be modeled as a lens with a focal distance of 25 cm on the side of the object and a focal distance of 22 mm on the side of the image (retina) with an open aperture of 8 mm in diameter placed on the object side of the lens to limit the light entry, i.e. the open aperture is preferentially located immediately in front of the lens. In another embodiment, the open aperture can also be located immediately behind the open aperture. The local intensity on a retina of a healthy human eye of a second laser beam is therefore preferentially defined as the intensity of the second laser beam at the image plane, if the subdividing and redirection element is placed at the focal point of such a lens at the object side with the open aperture of 8 mm immediately in front of or behind the lens.

It is further preferred that the lighting apparatus is adapted such that the average intensity on a retina of a healthy human eye of the entire second laser beams is below a predefined threshold related to safety, if the second laser beams are directed to the healthy human eye. In particular, this predefined threshold is equal to or smaller than 10³ Wcm^~2 . It is further preferred that this predefined threshold is equal to or smaller than 10² Wcm^~2. The average intensity on a retina of a healthy human eye of the entire second laser beams is preferentially defined as the power of the second laser beams divided by the area of the image on the retina caused by the second laser beams. The lighting apparatus is preferentially adapted such that, if the lighting apparatus is directed onto the human eye such that the average intensity on the retina of a healthy human eye is maximized, this maximal average intensity is still below the predefined threshold.

The lighting apparatus is preferentially adapted such that the power of the second laser beams on the retina is predefined, wherein

- a minimal area of the image caused by the second laser beams on the retina is defined by a) the predefined power of the second laser beams on the retina and b) the predefined threshold for the average intensity of the second laser beams on the retina, if the second laser beams are directed to a healthy human eye,

- an image expansion factor is defined as the ratio of a) the minimal area of the image on the retina obtained if the second laser beams are directed to a healthy human eye to b) the area of an image on a retina obtained if the subdividing and redirection element is removed, if the first laser beam is collimated and if the first laser beam is directed to the healthy human eye, - each of the second laser beams comprises a cross-section at the position of the subdividing and redirection element, wherein a maximal cross-section area is defined as the maximal area of the areas of the cross-sections of the second laser beams at the position of the subdividing and redirection element,

- the lighting apparatus is adapted such that the maximal cross-section area is smaller than the area of the cross-section of the first laser beam at the position of the subdividing and redirection element divided by the image expansion factor. This means, in an embodiment, the power of the second laser beams is given and the lighting apparatus is adapted such that the above mentioned condition with respect to the cross- sections is fulfilled. This leads generally to a local intensity of each second laser beam and an average intensity of the entire second laser beams on a retina of a healthy human eye, which are smaller than the predefined threshold related to safety.

If it is assumed that the healthy human eye can be modeled by the above mentioned lens with a focal distance of 25 cm on the side of the object and a focal distance of 22 mm on the side of the image (retina) with an open aperture of 8 mm in diameter placed on the object side or the image side of the lens to limit the light entry, the average intensity on a retina of a healthy human eye of the entire second laser beams is preferentially defined as the power of the entire second laser beams imaged in the image plane divided by the area of the image at the image plane caused by the second laser beams, if the subdividing and redirection element is placed at the focal point of such a lens at the object side with the open aperture of 8 mm immediately in front of or behind the lens.

It is further preferred that the first laser beam is expanded such that the average intensity on a retina of a healthy human eye of the entire second laser beams is below the predefined threshold related to eye safety. This condition defines a minimal diameter and/or area of the cross-section of the first laser beam at a predefined position, which is preferentially the position of the subdividing and redirection element.

It is further preferred that, if the second laser beams are directed to a lens, if the subdividing and redirection element is placed at a focal point of the lens at an object side of the lens, if the lens has a focal distance of 25 cm on the object side and a focal distance of 22 mm on the image side and if an open aperture with a diameter of 8 mm is located on the lens,

- the lighting apparatus is adapted such that the power of the second laser beams in an image plane of the lens is predefined,

- a minimal area of the image caused by the second laser beams in the image plane of the lens is defined by a) the predefined power of the second laser beams in the image plane of the lens and b) the predefined threshold for the average intensity of the second laser beams in the image plane of the lens

- an image expansion factor is defined as the ratio of a) the minimal area of the image in the image plane of the lens to b) the area of an image in the image plane obtained if the subdividing and redirection element is removed, if the first laser beam is collimated and if the first laser beam is directed to the lens,

- each of the second laser beams comprises a cross-section at the position of the subdividing and redirection element, wherein a maximal cross-section area is defined as the maximal area of the areas of the cross-sections of the second laser beams at the position of the subdividing and redirection element,

Given the power of the second laser beams, the predefined threshold for the average intensity of the entire second laser beams on the retina defines a minimal area of the image caused by the second laser beams on the retina, which is correlated with the minimal diameter and/or area of the cross-section of the first laser beam at the position of the subdividing and redirection element by the optical paths from the subdividing and redirection element to the retina. In particular, the minimal area of the image caused by the second laser beams is achieved, if the above defined minimal diameter and/or area of the cross-section of the first laser beam is used. This minimal area of the image on the retina divided by the area of an image on the retina achieved if the subdividing and redirection element is removed defines the image expansion factor, in the case that the first laser beam is collimated and therefore parallel.

In an embodiment, the lighting apparatus is adapted such that the local intensity of each second laser beam and the average intensity of the entire second laser beams on a retina of a healthy human eye are each smaller than a predefined threshold. This predefined threshold is preferentially equal to or smaller than 10³ Wcm^~2 and further preferred equal to or smaller than 10² Wcm^~2.

In an embodiment, the subdividing and redirection regions are adapted such that the second laser beams have different cross-sections and/or shapes. These different cross-sections and/or shapes of the second laser beams are preferentially random cross-sections and/or shapes, respectively, i.e. they are irregular and do not follow a certain rule. This diminishes the probability of occurrence of interference peaks caused by the interference of second laser beams. These interference peaks could yield an increased local intensity. By diminishing the probability of occurrence of these interference peaks, the eye safety is further improved.

It is further preferred that the subdividing and redirection element comprises a surface having a surface relief, wherein the subdividing and redirection regions are defined by surface regions on the surface and wherein different subdividing and redirection regions are defined by different surface regions having different surface reliefs for subdividing the first laser beam into several second laser beams, which propagate at least in part in different directions.

In an embodiment, the subdividing and redirection regions, i.e. e.g. the surface reliefs, are adapted such that all second laser beams are directed into different directions. In another embodiment, the subdividing and redirection regions are adapted such that several but not all second laser beams are directed into different directions.

The surface of the subdividing and redirection element preferentially comprises an antireflection coating. This increases the transmission and therefore further improves the efficiency of the lighting apparatus, if the lighting apparatus is used in a transmission mode.

In an embodiment the subdividing and redirection element is used in a reflection mode such that an observer cannot look directly into the laser in the event that the subdividing and redirection element is removed. This means the second laser beams are subdivided and redirected by reflection such that the second laser beams substantially do not transmit through the redirection and subdividing element.

It is further preferred that the lighting apparatus comprises a coherence reduction element for reducing the degree of coherence of the first laser beam and/or the second laser beams. In a preferred embodiment, the coherence reduction element is adapted to eliminate the coherence of the first laser beam and/or of the second laser beams. The coherence reduction element is preferentially adapted to use methods for reducing coherence induced interference effects such as placing segmented time varying mechanically rotating retarders. However, it is also possible to use electrically addressable elements such as those based on liquid crystals as coherence reduction elements.

In an embodiment, the laser emits a divergent first laser beam being collimated by a collimation element like a lens and the collimated first laser beam is directed onto the subdividing and redirection element. Preferentially, before meeting the subdividing and redirection element the collimated first laser beam traverses the coherence reduction element.

The subdividing and redirection element can be formed as a screen, which might be a micro lens array. The micro lens array can be an engineered micro lens array composed of micro lenses of different sizes and shapes to produce any desired intensity profile of a third laser beam formed by the second laser beams with high efficiency. Each micro lens can be regarded as defining a subdividing and redirection region.

In an embodiment, the subdividing and redirection element and the coherence reduction element are integrated in a single unit. For example the subdividing and redirection element can be adapted to move in front of the laser for reducing the coherence.

It is further preferred that the subdividing and redirection element is formed as a screen and that the lighting apparatus further comprises an image forming element for forming an image on the screen. In an embodiment, the image forming element forms a pattern on the screen. This pattern can be active, wherein the image forming element comprises, for example, a scanning device such as a mirror galvanometer or micro mechanical devices or spatial light modulators or a diffractive and/or refractive and/or reflective optical element to produce complex patterns.

The screen can comprise the above mentioned surface having a surface relief, wherein in an embodiment the image is formed on this surface of the screen.

It is further preferred that the lighting apparatus comprises a projection element for projecting the image, which is formed on the screen, on a projection area. The projection element is preferentially a projection lens, which projects the image on the screen onto the projection area. The projection element is preferentially located between the subdividing and redirection element and the projection area. The image can also be projected directly onto a retina of a human eye.

In a further aspect of the present invention a lighting method is presented, wherein the lighting method comprises following steps:

- providing a laser for emitting a first laser beam,

- providing a subdividing and redirection element comprising several subdividing and redirection regions, wherein the subdividing and redirection regions are adapted such that, if the first laser beam illuminates several of the subdividing and redirection regions, from each of these illuminated subdividing and redirection regions a second laser beam originates by refraction or reflection, wherein at least two second laser beams propagate at least in part in different directions,

- emitting a first laser beam by the laser,

- illuminating several of the subdividing and redirection regions by the first laser beam such that from each of these illuminated subdividing and redirection regions a second laser beam originates by refraction or reflection, wherein at least two second laser beams propagate at least in part in different directions.

It shall be understood that the lighting apparatus of claim 1 and the lighting method of claim 15 have similar and/or identical preferred embodiments as defined in the dependent claims.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the following drawings:

Fig. 1 shows schematically and exemplarily a representation of a lighting apparatus in a transmission mode, Fig. 2 shows schematically and exemplarily a further representation of a lighting apparatus comprising a beam expanding unit in a transmission mode, Fig. 3 shows schematically and exemplarily a further representation of a lighting apparatus comprising a collimation element in front of the subdividing and redirection element in a transmission mode, Fig. 4 shows schematically and exemplarily a further representation of a lighting apparatus comprising a collimation element behind a subdividing and redirection element in a transmission mode, Fig. 5 shows schematically and exemplarily a further representation of a lighting apparatus in a reflection mode, Fig. 6 shows schematically and exemplarily a further representation of a lighting apparatus comprising a coherence reduction element in a transmission mode, Fig.7 shows schematically and exemplarily a further representation of a lighting apparatus comprising an image forming element in a transmission mode, and Fig. 8 shows exemplarily a flowchart illustrating an embodiment of a lighting method. DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows schematically and exemplarily a lighting apparatus 1 in a transmission mode. The lighting apparatus comprises a laser 2 for emitting a first laser beam 3. The laser 2 is a laser diode in this embodiment. In other embodiments the laser could also be of another type of laser like another type of solid-state laser, a gas laser, a dye laser, a free electron laser et cetera.

The lighting apparatus 1 further comprises a subdividing and redirection element 4 comprising several subdividing and redirection regions 5, wherein the subdividing and redirection regions 5 are adapted such that, if the first laser beam 3 illuminates several of the subdividing and redirection regions 5, from each of these illuminated subdividing and redirection regions 5 a second laser beam 6 originates by refraction, wherein at least two second laser beams 6 propagate at least in part in different directions. The lighting apparatus 1 is adapted to expand the first laser beam before meeting the subdividing and redirection element 4 such that several subdividing and redirection regions 5 are illuminated. In this embodiment, the first laser beam 3 is divergent and a desired expansion is obtained by choosing a corresponding distance between the laser 2 and the subdividing and redirection element 4.

The subdividing and redirection regions 5 are adapted such that the second laser beams 6 form a third laser beam 7. The different second beams 6 are formed by rays 23 and preferentially overlap and/or meet each other while propagating and form the third laser beam 7, wherein the divergence of the third laser beam 7 is preferentially larger than the divergence of the first laser beam 1. In this embodiment, also the divergence of the individual second laser beams 6 is altered by the subdividing and redirection regions 5, wherein the divergence of an individual second laser beam 6 is larger than the divergence of a segment 21 of the first laser beam 3 falling onto a subdividing and redirection region 5. In other embodiments, the divergence of the individual second laser beams might remain unchanged.

In this embodiment, the subdividing and redirection regions 5 are adapted such that all second laser beams 6 are directed in different directions. In another embodiment, the subdividing and redirection regions can be adapted such that not all second laser beams are directed in different directions.

The subdividing and redirection regions 5 subdivide the expanded first laser beam 3 into the second laser beams 6 and redirect the second laser beams 6 substantially by refraction and substantially without diffraction.

The lighting apparatus 1 is adapted such that the cross-section of the first laser beam 3 is expanded such that several of the subdividing and redirection regions 5 are within this cross-section, if the expanded first laser beam 3 is directed onto the subdividing and redirection element 4. The subdividing and redirection regions 5 are arranged such that different subdividing and redirection regions 5 are met by the first laser beam 3 at different parts of the expanded cross-section of the first laser beam 3.

The lighting apparatus 1 is adapted such that the local intensity on a retina of a healthy human eye of each of the several second laser beams 6 is below a predefined threshold related to safety. In particular, the predefined threshold is equal to or smaller than 10³ Wcm^~2 . It is further preferred that predefined threshold is equal to or smaller thanl 0²Wcm^"2.

It is assumed that the healthy human eye can still reasonably focus at a distance of 25 cm with a fully open iris with a diameter of 8 mm. Thus, the healthy human eye can be modeled as a lens with a focal distance of 25 cm on the side of the object and a focal distance of 22 mm on the side of the image (retina) with an open aperture of 8 mm in diameter placed on the object side of the lens to limit the light entry, i.e. the open aperture is preferentially located immediately in front of the lens. In another embodiment, the open aperture can also be located immediately behind the open aperture. The local intensity on a retina of a healthy human eye of a second laser beam is therefore defined as the intensity of the respective second laser beam 6 at the image plane, if the subdividing and redirection element 4 is placed at the focal point of such a lens at the object side with the open aperture of 8 mm immediately in front of or behind the lens. This local intensity is lower than the above mentioned predefined threshold related to human eye safety.

The lighting apparatus 1 is also adapted such that the average intensity on a retina of a healthy human eye of the entire second laser beams 6 is below a predefined threshold related to eye safety. In particular, this predefined threshold is equal to or smaller than 10³ Wcm^~2 . It is further preferred that this predefined threshold is equal to or smaller than 10² Wcm^~2. The average intensity on a retina of a healthy human eye of the entire second laser beams 6 is defined as the power of the second laser beams 6 divided by the area of the image on the retina caused by the second laser beams. The lighting apparatus 1 is adapted such that, if the lighting apparatus 1 is directed onto the healthy human eye such that the average intensity on the retina of a healthy human eye is maximized, this maximal average intensity is still below the predefined threshold.

As already mentioned above, it is assumed that the healthy human eye can be modeled by the above mentioned lens with a focal distance of 25 cm on the side of the object and a focal distance of 22 mm on the side of the image (retina) with an open aperture of 8 mm in diameter placed on the object side or the image side of the lens to limit the light entry. Therefore, the average intensity on a retina of a healthy human eye of the entire second laser beams is defined as the power of the entire second laser beams 6 imaged in the image plane divided by the area of the image at the image plane caused by the second laser beams 6, if the subdividing and redirection element 4 is placed at the focal point of such a lens at the object side with the open aperture of 8 mm immediately in front of or behind the lens.

The condition that the average intensity on a retina of a healthy human eye of the entire second laser beams 6 is below a predefined threshold related to human eye safety defines a minimal diameter and/or area of the cross-section of the first laser beam 3 at the position of the subdividing and redirection element 4.

Given the power of the second laser beams 6, the predefined threshold for the average intensity of the entire second laser beams 6 on the retina defines a minimal area of the image caused by the second laser beams 6 on the retina, which is correlated with the minimal diameter and/or area of the cross-section of the first laser beam 3 at the position of the subdividing and redirection element 4 by the optical paths from the subdividing and redirection element to the retina. In particular, the minimal area of the image caused by the second laser beams 6 is achieved, if the above defined minimal diameter and/or area of the cross-section of the first laser beam 3 is used. This minimal area of the image on the retina divided by the area of an image on the retina achieved if the subdividing and redirection element 4 is removed and if the first laser beam is collimated defines an image expansion factor.

The expansion of the first laser beam 3 is preferentially chosen such that the local intensity of each second laser beam 6 on a retina of a healthy human eye and the average intensity on a retina of a healthy human eye of the entire second laser beams 6 are below the above mentioned predefined threshold related to eye safety.

Each of the second laser beams 6 comprises a cross-section at the position of the subdividing and redirection element 4, wherein a maximal cross-section area is defined as the maximal area of the areas of the cross-sections of the second laser beams 6 at the position of the subdividing and redirection element 4. The lighting apparatus 1 is adapted such that the maximal cross-section area is smaller than the area of the cross-section of the first laser beam 1 at the position of the subdividing and redirection element 4 divided by the image expansion factor.

In a further embodiment, which is schematically and exemplarily shown in Fig. 2, the lighting apparatus 8 comprises a beam expanding unit 9 for expanding the first laser beam 3. The beam expanding unit 9 is preferentially adapted to expand the cross- section of the first laser beam 3 such that the above mentioned conditions with respect to the local intensity of each individual second laser beam 6 and with respect to the average intensity of the entire second laser beams 6 are fulfilled.

Fig. 3 shows a further embodiment 11 , which differs from the embodiment shown in Fig. 1 in that the first laser beam 3 is collimated by a collimation lens 10 before meeting the subdividing and redirection element 4. Also in this embodiment and the further embodiments illustrated in the description the cross-section of the first laser beam 3 is sized such that the above mentioned conditions with respect to the local intensity of each individual second laser beam 6 and with respect to the average intensity of the entire second laser beams 6 are fulfilled.

The subdividing and redirection regions 5 are adapted such that the second laser beams 6 have different cross-sections and/or shapes. These different cross- sections and/or shapes of the second laser beams 6 are random cross-sections and/or shapes, respectively, i.e. they are irregular and do not follow a certain rule. The second laser beams 6 could also have the same cross-section.

The subdividing and redirection element 4 comprises a surface 20 having a surface relief 12, wherein the subdividing and redirection regions 5 are defined by surface regions 5 on the surface 20 and wherein different subdividing and redirection regions 5 are defined by different surface regions having different surface reliefs 12 for subdividing the first laser beam 3 into several second laser beams 6, which are directed into different directions.

The surface 12 of the subdividing and redirection element 4 comprises an antireflection coating which is not shown in the figures.

In another embodiment, the subdividing and redirection element can be formed as a array of micro lens elements, which are preferentially parts of a lens which can be parabolic, elliptical or spherical. The micro lens elements define the second laser beams; in particular, each micro lens element defines a second laser beam. By tailoring the surface profile of each micro lens element and the overall distribution of micro lenses in the array it is possible to control the resulting light pattern. Within the array each one of these parameters can be varied and optimized to attain the desired intensity profile and beam angles, while ensuring enough randomization to guarantee light homogenization. The statistical properties of the elements are then preferentially characterized by probability distribution functions that define the range and type of randomness associated with a given parameter.

A subdividing and redirection element can be produced by coating a transparent substrate like a glass substrate with a uniform layer of a photosensitive polymer which is then exposed to a focused laser beam to produce a desired surface relief. After developing the resist the desired surface pattern is obtained.

Fig. 4 shows a further embodiment of a lighting apparatus 26 in a transmission mode. A collimator lens 28 is located behind a subdividing and redirection element 34, which is similar to the subdividing and redirection element 4 shown in Figs. 1 to 3 and 6, i.e. also the subdividing and redirection element 34 comprises subdividing and redirection regions 35, wherein from each of these subdividing and redirection regions 35 a second laser beam 6 originates by refraction or reflection and wherein at least two second laser beams 6 propagate at least in part in different directions. The lens 28 transforms the third beam 7 to a collimated third beam 24. In this way a highly collimated eye safe laser light is obtained. For this purpose, preferentially the subdividing and redirection element 34 is adapted to provide a flat top intensity profile of the collimated third laser beam 24, i.e. in particular the intensity is constant as a function of angle in a certain angular range before it goes to zero rapidly above this angular range. In particular, the surface relief of the subdividing and redirection element 34 or a micro lens array of a subdividing and redirection element is adapted to obtain such a profile.

Also in the embodiments shown in Figs. 1 to 3 and 6 a collimator lens 10 can be located behind the subdividing and redirection element 4.

Fig. 5 shows an embodiment of a lighting apparatus 27 in a reflection mode, i.e. a reflective subdividing and redirection element 25 is used. The lighting apparatus 27 comprises a laser 2 for emitting a first laser beam 3 and the reflective subdividing and redirection element 25 comprising several reflective subdividing and redirection regions 38. The subdividing and redirection regions 38 are adapted such that, if the first laser beam 3 illuminates several of the subdividing and redirection regions 38, from each of these illuminated subdividing and redirection regions 38 a second laser beam 6 originates by reflection, wherein at least two second laser beams 6 propagate at least in part in different directions. The second laser beams 6 form a third laser beam 7. The reflective subdividing and redirection element 25 comprises a reflective surface relief 30, wherein the reflective reliefs of the reflective surface relief 30 define the subdividing and redirection regions 38. In this embodiment, the first laser beam 3 is collimated by a collimator lens 29 before meeting the subdividing and redirection element 25. Also the lighting apparatus 27 is adapted such that the cross-section of the first laser beam 3 is sized such that the above mentioned conditions with respect to the local intensity of each individual second laser beam 6 and with respect to the average intensity of the entire second laser beams 6 are fulfilled.

The main advantage of the reflective subdividing and redirection element 25 is that, if the reflective subdividing and redirection element 25 is removed, for example, by accident, an observer is not exposed to a direct laser beam. Also the configurations, which are illustrated with respect to a transmission subdividing and redirection element in the description, can correspondingly be used with a reflective subdividing and redirection element.

The lighting apparatus can comprise a coherence reduction element for reducing the degree of coherence of the first laser beam and/or the second laser beams. In a preferred embodiment, the coherence reduction element is adapted to eliminate the coherence of the first laser beam and/or of the second laser beams. For example, in the embodiments illustrated in this description the coherence reduction element can be placed before or behind the subdividing and redirection element.

The coherence reduction element is preferentially adapted to use methods for reducing coherence induced interference effects such as placing segmented time varying mechanically rotating retarders which can be addressed electrically or mechanically.

Speckle arises when coherent light scattered from a rough surface, such as a screen, is detected by a square-law detector with a finite aperture, such as an observer's human eye. The image on the screen appears to be quantized into areas with sizes equal to the detector resolution spot. The detected spot intensity varies randomly from darkest, if contributions of the scattering points inside the spot interfere destructively, to brightest if they interfere constructively. This spot-to-spot intensity fluctuation is referred to as speckle. An electrically varying element to avoid speckle, which can be used as coherence reduction element, is for example described in WO 2008/087575 Al.

Fig. 6 shows a further embodiment of a lighting apparatus 12. The laser 2 emits a divergent first laser beam 3 being collimated by a collimation element 10 like a lens and the collimated first laser beam is directed onto the subdividing and redirection element 4. Before meeting the subdividing and redirection element 4 the collimated first laser beam traverses a coherence reduction element 13. In another embodiment, the coherence reduction element 13 can also be arranged between the laser 2 and the collimation element 10 or behind the subdividing and redirection element 4.

Fig. 7 shows a further embodiment of a lighting apparatus 14. The lighting apparatus 14 comprises the subdividing and redirection element 4 which is formed as a screen and an image forming element 15 for forming an image 18 on the screen 4. For example, the image forming element 15 can be adapted to form a pattern on the screen 4. This pattern can be active, wherein the image forming element comprises, for example, a scanning device such as a mirror galvanometer or micro mechanical devices or spatial light modulators or a diffractive and/or refractive and/or reflective optical element to produce complex patterns. Such patterns can for example be used in automotive lighting, general lighting, decorative lighting et cetera.

The screen 4 preferentially comprises the above mentioned surface having a surface relief for making the beam eye safe, wherein in an embodiment the image 18 is formed on this surface of the screen 4.

After the first laser beam 3 has passed the subdividing and redirection element 4, i.e. the screen 4, second laser beams are generated which form a third laser beam 19. In Fig. 7 only the third laser beam 19 is shown and not the individual second laser beams forming the third laser beam 19. Preferentially, the third laser beam becomes divergent mainly in the forward direction at multiple positions with a small loss.

The third laser beam 19 passes the coherence reduction element 13 and a projection element 16, which is for example a projection lens, for projecting the image 18 on a projection area 17, which can be an illumination surface, on which the image should be shown. In this way an eye safe laser based illuminator is obtained. The image can also be imaged directly on a retina of a human eye.

In the following an embodiment of a lighting method will be exemplarily described with reference to a flowchart shown in Fig. 8.

In step 101 a laser 2 for emitting a first laser beam 3 and in step 102 a subdividing and redirection element 4 comprising several subdividing and redirection regions 5 are provided, wherein the subdividing and redirection regions 5 are adapted such that, if the first laser beam 3 illuminates several of the subdividing and redirection regions 5, from each of these illuminated subdividing and redirection regions 5 a second laser beam 6 originates by refraction or reflection, wherein at least two second laser beams propagate at least in part in different directions.

In step 103 the first laser beam 3 is emitted by the laser 2 and in step 104 the first laser beam 3 is expanded. Then, in step 105 several of the subdividing and redirection regions 5 are illuminated by the expanded first laser beam 3 such that from each of these illuminated subdividing and redirection regions 5 a second laser beam 6 originates by refraction or reflection, wherein at least two second laser beams propagate at least in part in different directions. It should be noted that steps 103 to 105 are performed substantially simultaneously, i.e. with the speed of light. Furthermore step 102 can be performed before step 101. Step 104 can be omitted.

Laser eye safety is one of the important points when it comes to using lasers in consumer applications. By expanding the first laser beam the apparent surface area is increased and the subdividing and redirection element generates second laser beams forming a third laser beam having preferentially a reduced degree of collimation in comparison to the collimation of the first laser beam. The increased apparent surface, the reduced degree of collimation and the optional coherence reduction element that reduces constructive interference effects improve or generate eye safety.

Although in the above described embodiment the subdividing and redirection element and the coherence reduction element are separate elements, they can also be integrated in a single element.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

A single unit or devices may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A lighting apparatus comprising a laser (2) for emitting a first laser beam (3) and a subdividing and redirection element (4; 25; 34) comprising several subdividing and redirection regions (5; 35; 38), wherein the subdividing and redirection regions (5; 35; 38) are adapted such that, if the first laser beam (3) illuminates several of the subdividing and redirection regions (5; 35; 38), from each of these illuminated subdividing and redirection regions (5; 35; 38) a second laser beam (6) originates by refraction or reflection, wherein at least two second laser beams (6) propagate at least in part in different directions.

2. The lighting apparatus as defined in claim 1, wherein the lighting apparatus is adapted to expand the first laser beam (3) before meeting the subdividing and redirection element (4; 25; 34) such that the several subdividing and redirection regions (5; 35; 38) are illuminatable.

3. The lighting apparatus as defined in claim 1, wherein the subdividing and redirection regions (5; 35; 38) are adapted to direct the second laser beams (6) such that the divergence of the first laser beam (3) is different to the divergence of a third laser beam (7) formed by the second laser beams (6).

4. The lighting apparatus as defined in claim 1, wherein at least some of the subdividing and redirection regions (5; 35; 38) are adapted to increase the divergence of the individual second laser beams (6) in comparison to the divergence of the first laser beam (3).

5. The lighting apparatus as defined in claim 1, wherein the lighting apparatus is adapted such that the intensity on a retina of a healthy human eye of each of the several second laser beams (6) is below a predefined threshold related to eye safety, if the second laser beams (6) are directed to the healthy human eye.

6. The lighting apparatus as defined in claim 1, wherein the lighting apparatus is adapted such that the intensity of each second laser beam (6) in an image plane of a lens is below a predefined threshold related to eye safety, if the subdividing and redirection element (4; 25; 34) is placed at a focal point of the lens at an object side of the lens, if the lens has a focal distance of 25 cm on the object side and a focal distance of 22 mm on the image side and if an open aperture with a diameter of 8 mm is located on the lens.

7. The lighting apparatus as defined in claim 1, wherein the lighting apparatus is adapted such that the average intensity on a retina of a healthy human eye of the entire second laser beams (6) is below a predefined threshold related to eye safety, if the second laser beams are directed to the healthy human eye.

8. The lighting apparatus as defined in claim 7, wherein

- the lighting apparatus is adapted such that the power of the second laser beams (6) on the retina is predefined,

- a minimal area of the image caused by the second laser beams (6) on the retina is defined by a) the predefined power of the second laser beams (6) on the retina and b) the predefined threshold for the average intensity of the second laser beams (6) on the retina, if the second laser beams (6) are directed to a healthy human eye,

- an image expansion factor is defined as the ratio of a) the minimal area of the image on the retina obtained if the second laser beams (6) are directed to a healthy human eye to b) the area of an image on a retina obtained if the subdividing and redirection element (4; 25; 34) is removed, if the first laser beam (3) is collimated and if the first laser beam (3) is directed to the healthy human eye, - each of the second laser beams (6) comprises a cross-section at the position of the subdividing and redirection element (4; 25; 34), wherein a maximal cross- section area is defined as the maximal area of the areas of the cross-sections of the second laser beams (6) at the position of the subdividing and redirection element (4; 25; 34),

- the lighting apparatus is adapted such that the maximal cross-section area is smaller than the area of the cross-section of the first laser beam (3) at the position of the subdividing and redirection element (4; 25 ; 34) divided by the image expansion factor.

9. The lighting apparatus as defined in claim 1, wherein the lighting apparatus is adapted such that the average intensity of the entire second laser beams (6) in an image plane of a lens is below a predefined threshold related to eye safety, if the subdividing and redirection element (4; 25; 34) is placed at a focal point of the lens at an object side of the lens, if the lens has a focal distance of 25 cm on the object side and a focal distance of 22 mm on the image side and if an open aperture with a diameter of 8 mm is located on the lens.

10. The lighting apparatus as defined in claim 9, wherein, if the second laser beams (6) are directed to a lens, if the subdividing and redirection element (4; 25; 34) is placed at a focal point of the lens at an object side of the lens, if the lens has a focal distance of 25 cm on the object side and a focal distance of 22 mm on the image side and if an open aperture with a diameter of 8 mm is located on the lens,

- the lighting apparatus is adapted such that the power of the second laser beams (6) in an image plane of the lens is predefined,

- a minimal area of the image caused by the second laser beams (6) in the image plane of the lens is defined by a) the predefined power of the second laser beams (6) in the image plane of the lens and b) the predefined threshold for the average intensity of the second laser beams (6) in the image plane of the lens,

- an image expansion factor is defined as the ratio of a) the minimal area of the image in the image plane of the lens to b) the area of an image in the image plane obtained if the subdividing and redirection element (4; 25; 34) is removed, if the first laser beam (3) is collimated and if the first laser beam (3) is directed to the lens,

- each of the second laser beams (6) comprises a cross-section at the position of the subdividing and redirection element (4; 25; 34), wherein a maximal cross- section area is defined as the maximal area of the areas of the cross-sections of the second laser beams (6) at the position of the subdividing and redirection element (4; 25 ; 34),

- the lighting apparatus is adapted such that the maximal cross-section area is smaller than the area of the cross-section of the first laser beam (3) at the position of the subdividing and redirection element (4; 25; 34) divided by the image expansion factor.

11. The lighting apparatus as defined in claim 1 , wherein the subdividing and redirection regions (5; 35; 38) are adapted such that the second laser beams (6) have different cross-sections and/or shapes.

12. The lighting apparatus as defined in claim 1, wherein the subdividing and redirection element (4; 25; 34) comprises a surface having a surface relief, wherein the subdividing and redirection regions (5; 35; 38) are defined by surface regions on the surface and wherein different subdividing and redirection regions (5; 35; 38) are defined by different surface regions having different surface reliefs for subdividing the first laser beam (3) into several second laser beams (6), which propagate at least in part in different directions.

13. The lighting apparatus as defined in claim 1, wherein the lighting apparatus further comprises a coherence reduction element (13) for reducing the degree of coherence of the first laser beam (3) and/or the second laser beams (6).

14. The lighting apparatus as defined in claim 1, wherein the subdividing and redirection element (4; 25; 34) is formed as a screen and wherein the lighting apparatus further comprises an image forming element (15) for forming an image on the screen.

15. A lighting method comprising following steps:

- providing a laser (2) for emitting a first laser beam (3),

- providing a subdividing and redirection element (4; 25; 34) comprising several subdividing and redirection regions (5; 35; 38), wherein the subdividing and redirection regions (5; 35; 38) are adapted such that, if the first laser beam (3) illuminates several of the subdividing and redirection regions (5; 35; 38), from each of these illuminated subdividing and redirection regions (5; 35; 38) a second laser beam (6) originates by refraction or reflection, wherein at least two second laser beams (6) propagate at least in part in different directions,

- emitting a first laser beam (3) by the laser (2),

- illuminating several of the subdividing and redirection regions (5; 35; 38) by the first laser beam (3) such that from each of these illuminated subdividing and redirection regions (5; 35; 38) a second laser beam (6) originates by refraction or reflection, wherein at least two second laser beams (6) propagate at least in part in different directions.