Patent Description:
An illumination device as outlined above is for example disclosed in the International patent application no. The illumination device described therein allows the use of a reflector part composed of a plurality of concave shaped reflectors in different number, shapes and sizes (i.e. linear and/or area configurations). Such illumination device provides a good-quality lighting solution for direct replacement of so-called T5 fluorescent lamps in office and other indoor applications. The illumination device according to <CIT> consists of a reflector part formed of several concave shaped reflectors, wherein each reflector interacts with a LED light source.

The thickness dimension of an illumination device according to <CIT> is substantial, increasing its weight, making transportation and mounting or installation difficult and expensive. Furthermore, the reflector part is a complex and thus equally expensive component. Also, there is a large light intensity contrast between the small very bright light spots within the reflector part and the remainder of the reflector part, resulting in an unpleasant look and feel experience.

Document <CIT> discloses an illumination device comprising an optical element which is light transmissive and includes a pattern of concavities.

It is desirable to provide an illumination device of the above known kind, which is of a less complex and expensive construction and which is yet capable of emitting a more uniform light emission distribution of diffuse lighting.

Accordingly, an illumination device is proposed comprising a support structure having a first side with mounted thereon an array of a plurality of spatially separated solid state lighting elements, and an optical element made of a solid, light transmissive, light diffusing, foam material, wherein the optical element is provided with a pattern of concaves, essentially each concave being formed by a recessed portion comprising a closed bottom wall, an elevated portion having an apex bordering an light exit window downstream and opposite to the closed bottom wall, and a circumferential side wall extending from the closed bottom wall to the light exit window, wherein the plurality of spatially separated solid state elements is arranged outside and upstream of the concaves and conformal to said pattern of concaves.

The optical element, being mounted directly on the array of plurality of spatially separated solid state lighting elements, combines the functionality of a light reflector part, attributed by the recessed portions functioning as reflectors, and that of a light diffusor part, attributed by the light diffusing material. In addition, the optical element provides a partial shielding of light, in particular at high angles, thus providing lower glare. Next to a less complex configuration, also a reduction in constructional dimensions can be achieved, both resulting in simple yet less expensive design.

It is further noted that the expression "essentially each concave" means at least <NUM>% of the number of concaves, for example up to and including all concaves. The expression downstream (and upstream) is related to the propagation direction of light as emitted by the solid state light sources and the emission direction of the illumination device. Concaves typically widen from the closed bottom wall to the light exit window, or in other words, taper from the open light exit window to the closed bottom wall, and are typically shaped as reflector cups. The light exit window may be open or may be closed with, for example, a transparent plate or optics. Conformal to concaves can be one of conformal to the recessed portions or conformal to the elevated portions.

The illumination device may have the feature that the optical element has a back surface and a front surface opposite to the back surface of the optical element, wherein the optical element is mounted with said back surface on said first side of the support structure and downstream of the solid state elements, and wherein a maximum thickness D between the back surface and the front surface at the apex of the elevated portions of the optical element is at least two times larger than the thickness Tr between the back surface and the front surface at the recessed portions. The thickness Tr is the measured (local) thickness in/of bulk material in a direction perpendicular to the light exit window and closed bottom wall. At least the whole front surface is downstream of the solid state elements, i.e. the solid state elements neither protrude from the back surface through the front surface into the concaves, nor are arranged in the concaves, but are completely upstream, i.e. behind, the front surface and even optionally upstream of the whole back surface. Still further, the optical element is only provided with concaves having a closed bottom wall and essentially free from through holes, i.e. the back surface and front surface are essentially closed surfaces, optionally except for mounting holes for mounting the optical element to the support structure.

At the recessed portions light is emitted as a beam of relatively high intensity and in a relatively slightly diffused manner, light of said beam is partly collimated by the side walls. Yet, through the elevated portions relatively highly diffused light of relatively low intensity is emitted. This combined emission of light through recessed and elevated portions, with the indicated minimal difference in distance, provides an attractive light distribution with low glare, if any at all. The optical element has local thickness, measured as the shortest local distance between the back surface and the front surface of the optical element, the local thickness of the optical element is larger at the elevated portions than at the recessed portions. By arranging the array of the plurality of spatially separated solid state lighting elements conformal to the array of the plurality of recessed portions or conformal to the array of the plurality of elevated portions is, the provided light pattern can be varied.

The illumination device may have the feature that the thickness Tr is in between <NUM>*D and <NUM>*D, wherein D is the maximum thickness of the optical element at the apex of the elevated portion. This could alternatively be expressed as that the illumination device may have the feature that a maximum depth of the plurality of recessed portions amounts <NUM>-<NUM>% of a maximum thickness of the optical element.

The illumination device may have the feature that the back surface is essentially flat. The advantage is obtained of easily free positioning of solid state elements with respect to concaves to adjust/vary light pattern. The expression "essentially flat" means without protrusions and/or recesses, yet the illumination device may have the feature that the back surface comprises relatively shallow recesses configured to accommodate partly or completely recessed or embedded solid state elements. Yet, when recessed or embedded solid state elements are comprised, said solid state elements neither extend through nor protrude from said front surface.

The illumination device may have the feature that the optical element is made in one piece, which enables a relatively easy manufacture and/or assembly of the illumination device.

The illumination device may have the feature that the array of the plurality of recessed portions is conformal to the array of the plurality of spatially separated solid state lighting elements. Then, a respective solid state light element of the array of separated solid state lighting elements is associated with and aligned with a respective closed bottom wall of a respective reflector cup of the array of reflector cups, wherein said respective closed bottom wall is arranged in between said respective solid state element and said respective light exit window. So, in a preferred example, the array of the plurality of recessed portions is conformal to the array of the plurality of spatially separated solid state lighting elements, whereas in another preferred example the array of the plurality of elevated portions is conformal to the array of the plurality of spatially separated solid state lighting elements. With conformal it is meant that the orientation and position of the array of recessed portions or elevated portions overlap and are aligned with the orientation and position of the array of the plurality of spatially separated solid state lighting elements.

In either preferred examples, the array of the plurality of recessed portions is facing away from the support structure or the array of the plurality of recessed portions is facing towards the support structure. These configurations allow for different light distributions but also a different look of the luminaire, where a smooth exit surface provides a homogenous lighting experience.

In a preferred example, the optical element is made from a solid foam material, preferably a solid closed-cell, or bubble, foam material, in particular having a closed-cell volume of at least <NUM> volume-%, more in particular in the range of <NUM>-<NUM> volume-% and preferably of <NUM> volume-%. The air-foam boundaries between the closed-cells and the foam material act as small Fresnel reflectors, scattering the light being emitted by the solid state lighting elements as a uniform light emission distribution of diffuse light.

When in a further example of the disclosure, the closed-cells have a diameter in the range of <NUM>-<NUM>, an optimal light scattering effect is achieved. Closed-cell, also referred to as bubble, diameters less than <NUM> result in undesired high reflection and too much scattering/diffusion, while in the invention is aimed at high transmission and some level of diffusion obtainable by closed-cell diameters larger than <NUM>, i.e. in the order of about <NUM>. When the closed-cell is larger than <NUM> the transmission through the mechanically closed but optically transmissive (bottom wall) of the foam material is favorably high, yet then the obtained scattering effect is too small and the risk on undesired glare is too high.

In a further example, the pattern formed of the array of the plurality of recessed portions and the array of the plurality of elevated portions have a polygon-shaped, an elliptical-shaped or a pyramidal -shaped circumference.

The plurality of recessed portions are provided with a recessed circumferential side wall arranged under an angle α with respect to the plane of the structure, with α in a range of <NUM>° to <NUM>°, preferably in the range of <NUM>° to <NUM>°. Herewith a uniform light emission distribution of diffuse light is obtained, whilst sufficiently shielding off the light emission at higher angles towards the (office) space wherein the illumination device is installed for environmental compliance. The recessed portions are bordered by the closed bottom wall, the light exit window and the circumferential side wall, and taper in the upstream direction from the light exit window to the closed bottom wall.

In a further example, a maximum depth of the plurality of recessed portions amounts <NUM>-<NUM>% of a maximum thickness of the optical element, and in particular the optical element typically has a thickness of <NUM>-<NUM>, in particular <NUM>, and the thickness of the optical element at the location of, i.e. in front of, the solid state lighting element, for example an LED, is in the range of <NUM>-<NUM>, in particular <NUM>-<NUM>, such as <NUM>, the LED itself typically has a height of about <NUM>-<NUM>.

In a further aspect, the solid foam material has a light transmissivity T in the range of <NUM>%-<NUM>%, such as about <NUM>-<NUM>%, such as <NUM>%. The transmissivity T is dependent a. on the size and density of the closed cells in the foam and the thickness of the foam layer. Yet, the amount of light issued from the foam (for example, at the location of the solid state element) also is dependent on the reflectivity of the substrate on which the solid state lighting element is arranged. A higher transmissivity renders a higher efficacy of the lighting device, yet less scattering and hence a less spreading effect by the recessed portions (cups), while too low transmissivity renders the lighting device to become too inefficient as too much light losses occur as a result of too much internal reflection of light within the foam. For the abovementioned range of transmissivity it is considered that the reflectivity of the back foil or substrate is at least <NUM>%.

In a preferred example, the solid foam material is polyurethane.

In a further example according to the disclosure, the support structure is provided with a further array of a plurality of spatially separated solid state lighting elements mounted on the first side of the support structure and the optical element is provided with an auxiliary recess portion conformal to the further array of a plurality of spatially separated solid state lighting elements. Typically each reflector is associated with a respective solid state lighting elements, e.g. an LED, for a desired interaction.

Also in this example, in two embodiments are feasible with the auxiliary recess portion either facing away from the support structure or facing towards the support structure. These configurations allow for different illuminations, either diffuse or homogenous with two distinct sets of solid state lighting elements, thus providing additional functionality of the illumination device thus implemented.

As a further aspect, the disclosure also pertains to an optical element for use in an illumination device as described herein, the optical element being made of a solid, light transmissive, light diffusing, foam material and provided with a pattern of concaves, wherein essentially each concave is formed by a recessed portion comprising a closed bottom wall, an elevated portion bordering a light exit window downstream and opposite to the closed bottom wall, and a circumferential side wall extending from the closed bottom wall to the light exit window.

The invention further relates to a luminaire. The support structure may contain or comprise electric circuitry, such as a driver, and electric components for providing electric power to the several components of the illumination device, in particular the spatially separated solid state lighting elements, which, for example, are mechanically and electrically mounted to a first, upper surface of the support structure. The support structure can be composed entirely or partly as a printed circuit board (PCB). The support structure may be part of a housing of the illumination device and can be mounted with its second, other side to a ceiling of for example an office room, the second side being opposite from the first side on which the solid state lighting elements are mounted. The combination of the lighting device with at least one of the group comprising a housing, driver and components for providing electric power, may be considered a luminaire.

The disclosure will now be discussed with reference to the drawings which are not necessarily to scale and in which some dimensions will be exaggerated for explanatory reasons, which show in:.

For a proper understanding of the disclosure, in the detailed description below corresponding elements or parts of the disclosure will be denoted with identical reference numerals in the drawings.

<FIG>, combined with <FIG>, schematically illustrates a non-limiting example of an embodiment of an illumination device according to the present disclosure. Reference numeral <NUM> depicts the illumination device being composed of a support structure <NUM> and an optical element <NUM> mounted thereon. The support structure <NUM> is provided with a plurality of solid state lighting elements <NUM>. The plurality of solid state lighting elements <NUM> are spatially separated from each other.

For example, the plurality of spatially separated solid state lighting elements <NUM> are mounted on the support structure <NUM> in a two-dimensional array of rows and columns, as shown in <FIG>. In other embodiments, the plurality of spatially separated solid state lighting elements <NUM> can be arranged in a one-dimensional orientation on the support structure <NUM>, thus forming a single line or strip of solid state lighting elements <NUM>. In another example, even a three-dimensional orientation is feasible, with the support structure being formed as a three-dimensional profile conformal to a shape of an underlying construction to which the complete illumination device <NUM> is to be mounted. To this end, the support structure <NUM> can be made (in part) of a flexible material, allowing the support structure to conform to the shape of the underlying construction.

When powered or activated, the plurality of spatially separated solid state lighting elements <NUM> emit visible light. The support structure <NUM> may contain or comprise electric circuitry, such as a driver, and electric components for providing electric power to the several components of the illumination device <NUM>, in particular the spatially separated solid state lighting elements <NUM>, which are mechanically and electrically mounted to a first, upper surface 10a of the support structure <NUM>. The support structure <NUM> can be composed entirely or partly as a printed circuit board (PCB).

The support structure <NUM> may be part of a housing (not depicted) of the illumination device <NUM> and can be mounted with its second, other side 10b to a ceiling <NUM> of for example an office room, the second side 10b being opposite from the first side 10a on which the solid state lighting elements <NUM> are mounted. The combination of the lighting device with at least one of the group comprising a housing, driver and components for providing electric power, may be considered a luminaire.

The number of plurality of solid state lighting elements <NUM> can be arbitrarily chosen, and can be <NUM> or <NUM>, but preferably at least <NUM>. Suitable examples of an illumination device <NUM> for example for use in office spaces may comprise <NUM> or more, even <NUM>, <NUM>+ solid state lighting elements <NUM> per illumination device <NUM> depending on the size and application of the illumination device.

Returning to <FIG> and <FIG>, reference numeral <NUM> denotes an optical element. The optical element <NUM> is made from a light diffusing material, thus capable for diffusing light emitted by the array of the plurality of spatially separated solid state lighting elements <NUM>. In a preferred example, the optical (diffuser) element <NUM> is made from a solid foam material, such as polyurethane. Other examples are so-called microcell urethane foam (PORON), silicone foams and cross linked polyethylene foam (XLPE).

The optical (diffuser) element <NUM> has a back surface 12a and a front surface 12b (both denoted with a dashed line), the front surface 12b being opposite from the back surface 12a. According to the disclosure, the optical element <NUM> is directly mounted with its back surface 12a on the first side 10a of the support structure <NUM>. Preferably, the optical (diffuser) element <NUM> is formed as a foam block having longitudinal dimensions more or less identical to the longitudinal dimensions of the support structure <NUM>. The thickness D (see also <FIG>) of the foam-block shaped optical element <NUM> can be arbitrarily chosen, but such that it provides most of the mechanical strength of the complete construction of the illumination device <NUM>. Accordingly, the mechanical strength of the complete construction does not necessarily be provided by the support structure <NUM>.

The optical (diffuser) element <NUM> is provided with a pattern formed of an array of a plurality of recessed portions <NUM> and an array of a plurality of elevated portions <NUM>. In an example shown in <FIG> as well as in <FIG> and <FIG>, both the array of the plurality of recessed portions <NUM> and the array of the plurality of elevated portions <NUM> are provided in the front, other side 12b of the optical element <NUM>, away from the back surface 12a and the side 10b of the support structure <NUM> on which the solid state lighting elements <NUM> are mounted. See <FIG> and <FIG> for more detail.

However in another functional example as depicted in <FIG>, both the array of the plurality of recessed portions <NUM> and the array of the plurality of elevated portions <NUM> are provided in the back surface 12a of the optical element <NUM>, facing towards the side 10b of the support structure <NUM> on which the solid state lighting elements <NUM> are mounted.

In the example of <FIG> and <FIG>, the array of the plurality of recessed portions <NUM> is conformal to the array of the plurality of spatially separated solid state lighting elements <NUM>, whereas in the example of <FIG> the array of the plurality of elevated portions <NUM> is conformal to the array of the plurality of spatially separated solid state lighting elements <NUM>. Note, however, that the embodiment of <FIG> refers to a non-claimed example. With the term 'conformal' is meant, that the array of the plurality of recessed portions <NUM> (or elevated portions <NUM>) and the array of the plurality of spatially separated solid state lighting elements <NUM> overlap each other, with each solid state lighting element <NUM> facing a recessed portion <NUM> (<FIG>) or an elevated portion <NUM> (<FIG>). As such in both examples, the pattern composed of the arrays of the plurality of recessed portions <NUM> / elevated portions <NUM> can be configured in a two-dimensional array, or in a one-dimensional line (or single row) design, or even in a three-dimensional shape. In <FIG> the plurality of spatially separated solid state lighting elements <NUM> are partly embedded or recessed at the back surface 12a into the optical element <NUM>, while in <FIG> the plurality of spatially separated solid state lighting elements <NUM> are mounted in a non-recessed manner on the back surface 12a of the optical element <NUM>.

The optical element <NUM>, being mounted directly on the support structure <NUM>, functions as a light reflector part, attributed by the recessed portions <NUM>, which each function as an individual reflector for the respective, corresponding solid state light emitting device <NUM>. In addition, optical element <NUM> functions as a light diffusor part, attributed by the light diffusing material being a solid foam material. In addition, the optical (diffuser) element <NUM> provides a partial shielding of light, in particular at high angles, thus providing lower glare. Next to a less complex configuration, also a reduction in constructional dimensions can be achieved, both resulting in simple yet less expensive design.

Preferably, the solid foam material of the optical element is a solid closed-cell foam material, in particular having a closed-cell volume of at least <NUM> volume-%, more in particular of <NUM>-<NUM> volume-% and preferably of <NUM> volume-%. The air-foam boundaries between the closed-cells <NUM> and the foam material of the optical element <NUM> act as small Fresnel reflectors, scattering the light being emitted by the solid state lighting elements as a uniform light emission distribution of diffuse light.

Preferably, the closed-cells <NUM> have a diameter in the range of <NUM>-<NUM>, and herewith an optimal light scattering effect is achieved. The closed-cells <NUM> preferably have a uniform diameter, but more preferable a diameter distributed within the <NUM>-<NUM> range.

The optical element comprises concaves 12c comprising recessed portions or reflector cups <NUM> provided in the front side 12b of the optical element <NUM>. The recessed portions <NUM> have an open light exit window 120d and opposite thereto a closed bottom wall 120a, which faces the corresponding solid state light emitting device <NUM> (<FIG>). The optical element <NUM> has a thickness of about <NUM> in front of the solid state lighting element <NUM>, i.e. D-d ≈ <NUM>, wherein here D is the maximum thickness dimension of optical element <NUM> and d is the depth dimension of recessed portion <NUM> of optical element <NUM>. The closed bottom wall 120a preferably has a square or rectangular surface area, with x1 preferably being <NUM> x <NUM>. The open recessed portions or reflector cups <NUM> are further bound by a circumferential side wall120b. Between adjacent recessed portions or reflector cups <NUM> of the array of plurality of recessed portions or reflector cups <NUM> the array of elevated portions <NUM> are present, which constitute in this example intermediate wall sections 120c. The elevated portions <NUM> / intermediate wall sections 120c are flush with the front, other side 12b of the optical element <NUM> and may have a length dimension x2 of <NUM>, thus preventing the creation of an undesired shadow effect in under large angles. The open recessed portions or reflector cups <NUM> together with the elevated portions <NUM> / the intermediate wall sections 120c function as the light emission window of the illumination device <NUM>.

<FIG>, <FIG>, <FIG>, <FIG> and <FIG> show several further examples of the optical (diffuser) element, denoted with reference numerals <NUM>'-<NUM>"-<NUM>‴. In these examples, which conform with <FIG> and <FIG>, both the array of the plurality of recessed portions <NUM> and the array of the plurality of elevated portions <NUM> forming intermediate wall sections 120c are provided in the front, other side 12b of the optical element <NUM>, away from the back surface 12a and the side 10b of the support structure <NUM> on which the solid state lighting elements <NUM> are mounted. Furthermore, in these embodiments, the array of the plurality of recessed portions <NUM> is conformal to the array of the plurality of spatially separated solid state lighting elements <NUM> mounted on the support structure <NUM>.

In a first example, the plurality of recessed portions <NUM> of the optical element <NUM>' have a polygon-shaped circumference. <FIG> details such variant with square-shaped recessed portions <NUM>. <FIG> details another variant of an optical element <NUM>‴ with octagon-shaped recessed portions <NUM>. It should be noted that also other polygon-shaped variants can be implemented, which provide a different light emission distribution of diffuse and scattered light. <FIG>, <FIG> and <FIG> depict a variant of an optical element <NUM>"" with pyramid-shaped recessed portions <NUM> and likewise pyramid-shaped elevated portions <NUM> with the apex thereof denoted with reference numeral 120c as the apex can be considered as an intermediate wall section between adjacent pyramid-shaped recessed portions <NUM>.

In the example of <FIG>, the plurality of recessed portions <NUM> of the optical element <NUM>" have an elliptical-shaped circumference, in particular a circular circumference. Another example of the plurality of recessed portions <NUM> having an elliptical-shaped circumference is shown in <FIG> and <FIG>, depicting circular recessed portions <NUM> with a cone-shape.

Whereas the examples of <FIG>, <FIG>, <FIG>, <FIG> depict the array of the plurality of recessed portions <NUM> and the array of the plurality of elevated portions <NUM>, both having a regular pattern of rows and columns, the example of <FIG> and <FIG> depict an irregular pattern of the plurality of concaves 12d comprising recessed portions <NUM>, and the plurality of elevated portions <NUM>, the latter forming intermediate wall sections 120c. In the example of <FIG> the plurality of recessed portions <NUM> have a circular shape as in <FIG>, yet the array thereof has an irregular, pointillism pattern for example according to a Fibonacci sequence.

Note however, that these examples of <FIG>, <FIG>, <FIG>, <FIG> and <FIG> can be configured in a reversed configuration as illustrated in <FIG>, that is with both the array of the plurality of recessed portions <NUM> and the array of the plurality of elevated portions <NUM> being provided in the back surface 12a of the optical element <NUM>, facing towards the side 10b of the support structure <NUM> on which the solid state lighting elements <NUM> are mounted. For the optimal illuminance effect, in these reversed embodiments, the array of the plurality of elevated portions <NUM> should be conformal (meaning directly facing or overlapping) to the array of the plurality of spatially separated solid state lighting elements <NUM> mounted on the support structure <NUM>.

<FIG> and <FIG> depict two further embodiments of an illumination device according to the disclosure. In these embodiments, the support structure <NUM> is provided with the array of plurality of spatially separated solid state lighting elements <NUM>, which are mounted on the first side 10a of the support structure <NUM>. The array of plurality of spatially separated solid state lighting elements <NUM> is in this embodiment one of two distinct arrays, each array consisting of a plurality of spatially separated solid state lighting elements.

The pattern of the first array (denoted with reference numeral <NUM>-<NUM>) of plurality of spatially separated solid state lighting elements <NUM> is conformal to the pattern of the array of the plurality of recessed portions <NUM>, as outlined with respect to e.g. <FIG> and <FIG>. Similarly, the first array <NUM>-<NUM> of plurality of spatially separated solid state lighting elements <NUM> can be conformal to the pattern of the array of the plurality of elevated portions <NUM>, in a similar manner as outlined with respect to e.g. <FIG> and <FIG>.

Additionally, the support structure <NUM> is provided with a further array of plurality of spatially separated solid state lighting elements. This further array is denoted with reference numeral <NUM>-<NUM> and the plurality of spatially separated solid state lighting elements associated with this further array <NUM>-<NUM> are denoted with reference numeral <NUM>.

The plurality of spatially separated solid state lighting elements <NUM> and <NUM> belonging to each first and further array <NUM>-<NUM> and <NUM>-<NUM>, respectively, can be different from each other in terms of lighting color and can be controlled separately from each other by the control circuitry of the illumination device <NUM>. Alternatively, the solid state lighting elements <NUM> and <NUM> belonging to each first and further array <NUM>-<NUM> and <NUM>-<NUM> can be controlled in a simultaneous and identical manner.

The optical element <NUM> is provided with an auxiliary recess portion <NUM>, the shape (or geometrical dimensions) of the auxiliary recess portion being conformal to the shape (or geometrical dimensions) of the further array <NUM>-<NUM> of the plurality of spatially separated solid state lighting elements <NUM>. The shape or form of the auxiliary recess <NUM> can be arbitrarily chosen, for example in the shape of a cross as depicted in these examples.

Also in this example, two embodiments are depicted in <FIG> and <FIG>. In <FIG>, the auxiliary recess portion <NUM> is facing away from the support structure <NUM> as it is applied in the front surface or light emission window 12b of the optical element <NUM>, whereas in <FIG> the auxiliary recess portion <NUM> is facing towards the support structure <NUM> as the recess portion <NUM> is applied in the back surface 12a of the optical element <NUM>. Both configurations allow for different illuminations, either diffuse or homogenous light due to the separate control of the first and further array <NUM>-<NUM> and <NUM>-<NUM> of solid state lighting elements <NUM> and <NUM>, respectively. In particular, the light distribution from the separate solid state lighting elements <NUM> of the array <NUM>-<NUM> interacting with corresponding separate recessed portions or cups <NUM> create a more narrow light beam, resulting in a more office compliant lighting experience. The solid state lighting elements <NUM> of the other array <NUM>-<NUM>, which interact with the enlarged auxiliary recess <NUM> provide a uniform light distribution.

Thus, an additional functionality of the illumination device is provided. Although in <FIG> and <FIG> two separate arrays <NUM>-<NUM> and <NUM>-<NUM> of solid state lighting elements <NUM> and <NUM>, respectively are used, it is clear that more than two distinct arrays <NUM>-n (with n being <NUM>, <NUM>, <NUM> or more) can be implemented, each array interacting with different recesses <NUM>, <NUM>, etc..

Returning to <FIG> and <FIG>, the circumferential side wall 120b of each recessed portion <NUM> is arranged under an angle α with respect to the plane of the support structure <NUM>, the plane being formed by the first side 10a thereof. The angle α ranges between <NUM>° to <NUM>°, and preferably ranges between <NUM>° to <NUM>°. This range of angles α of the circumferential side wall 120b of each recessed portion <NUM> provide a uniform light emission distribution of diffuse light being emitted by the array of the plurality, corresponding solid state light emitting devices <NUM> and exiting the light emission window 12b, whilst sufficiently shielding off the light emission at higher angles towards the (office) space wherein the illumination device <NUM> is installed.

Please note, that the angle α of the side walls 120b of each recessed portion <NUM> is explained with reference to the embodiment of the recessed portion <NUM> having a circular, cone-shaped circumference (<FIG> and <FIG>). However, it is observed that the disclosed range of angles α equally applies to a side wall 120b of a recessed portion <NUM> having another circumferential shape. The angle α is equally applicable to a recessed side wall 120b of polygon-shaped recessed portion <NUM> as described in <FIG> and <FIG> as well as applicable to the reversed configuration of the optical element <NUM> of <FIG>.

Claim 1:
An illumination device (<NUM>) comprising a support structure (<NUM>) having a first side with mounted thereon:
- an array of a plurality of spatially separated solid state lighting elements (<NUM>), and
- an optical element (<NUM>) made of a solid, light transmissive, light diffusing, foam material,
wherein the optical element (<NUM>) is provided with a pattern of concaves (12d), essentially each concave (12c) being formed by:
- a recessed portion (<NUM>) comprising a closed bottom wall (120a),
- an elevated portion (<NUM>) having an apex bordering a light exit window (120d) downstream and opposite to the closed bottom wall (120a), and
- a circumferential side wall (120b) extending from the closed bottom wall (120a) to the light exit window (120d),
wherein the plurality of spatially separated solid state elements (<NUM>) is arranged outside and upstream of the concaves (12c) and conformal to said pattern of concaves (12d).