# US 12,000,583 B2 · Sun-sky-imitating illumination device

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- Number: US 12,000,583 B2
- Document ID: US12000583B2
- Status: Granted
- Kind: B2
- Application number: 17/442,249
- Filed: 2020-03-26
- Published: 2022-11-10
- Granted: 2024-06-04
- Earliest claimed: 2019-03-29
- Assignees: CoeLux S.r.l.
- Applicants: CoeLux S.r.l.
- Inventors: Matteo Molteni; Paolo Ragazzi; Antonio Lotti; Davide Magatti
- Web page: https://patentgrep.com/patent/US12000583B2

## CPC

- F21V 3/04: characterised by materials, surface treatments or coatings
- F21V 9/02: for simulating daylight (F21V9/04, F21V9/06 take precedence)
- F21V 3/049: {Patterns or structured surfaces for diffusing light, e.g. frosted surfaces}
- F21V 5/004: {using microlenses}
- F21V 11/06: using crossed laminae or strips {, e.g. grid-shaped louvers}; using lattices or honeycombs
- F21V 13/12: Combinations of only three kinds of elements
- G02B 27/30: Collimators
- F21Y 2105/10: comprising a two-dimensional [2D] array of point-like light-generating elements
- F21Y 2115/10: Light-emitting diodes [LED]
- F21V: FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- F21Y: INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED

## Abstract

A direct-light generator includes an optical unit positioned downstream of an output surface of a collimated light source and upstream from a first emitting surface with respect to a direct light direction. The optical unit includes a first planar light mixing element characterized by a first response function having a first angular profile with a peak having a first divergence angle, and a second planar light mixing element characterized by a second response function having a second angular profile with a peak having a second divergence angle. The first planar light mixing element at least partially intercepts collimated light exiting the output surface of the collimated light source and defines a unit input surface. The second planar light mixing element is positioned downstream of the unit input surface to at least partially intercept light crossing the unit input surface and to define a unit emitting surface.

## Claims

### Claim 1

An illumination device comprising:
a direct-light generator that comprises
a collimated light source configured to generate, from a primary light, a collimated light having a spatial modulation, the collimated light exiting an output surface positioned upstream from a first emitting surface from which a direct light is emitted;
a diffused-light generator that is positioned downstream of the direct-light generator and comprises a second emitting surface, the diffused-light generator being configured to emit diffused light at the second emitting surface; and
an optical unit positioned downstream of the output surface of the collimated light source and upstream from the first emitting surface, the optical unit comprising
a first planar light mixing element positioned so as to at least partially intercept the collimated light exiting the output surface of the collimated light source and to define a unit input surface, and
a second planar light mixing element positioned downstream of the unit input surface so as to at least partially intercept the light crossing the unit input surface and to define a unit emitting surface,
wherein the first planar light mixing element is spaced apart from the second emitting surface by a propagation distance d such that, at the second emitting surface, the spatial modulation of the collimated light subtends an angle that is less than or equal to a divergence angle of a response function of the first planar light mixing element.

### Claim 2 (depends on 1)

The illumination device of claim 1, wherein the first and second planar light mixing elements are spaced apart from each other by a minimum unit depth (z1) that is configured to obtain uniform luminance of the direct light that exits the first emitting surface of the direct-light generator.

### Claim 3 (depends on 1)

The illumination device of claim 1, wherein at least one of the first planar light mixing element and the second planar light mixing element is a low-angle white light diffuser characterized by a response function having an angular profile with a peak having a divergence angle, the low-angle white light diffuser being configured to cause a blurring of the peak in the luminance profile (Lcoll (x, y, θ, φ) of the collimated light exiting the output surface.

### Claim 4 (depends on 3)

The illumination device of claim 3, wherein the second planar light mixing element is a low-angle white light diffuser that is integrated in the diffused-light generator as a dispersion of transparent microparticles or a superficial random distribution of micro-refractors formed in at least one of the second emitting surface and a diffuser input surface of the diffused-light generator.

### Claim 5 (depends on 3)

The illumination device of claim 3, wherein the low-angle white light diffuser comprises at least one of:
a random distribution of micro-refractors formed in an outer surface of a transparent layer or bulk material, and
a dispersion of transparent microparticles in a transparent layer or bulk material,
wherein the microparticles and the layer or bulk material experience a refractive-index mismatch.

### Claim 6 (depends on 1)

The illumination device of claim 1, wherein the first planar light mixing element is a micro-optical light mixer comprising a pair of micro-lens arrays, wherein each micro-lens of a first array of the pair of micro-lens arrays is positioned at a focal distance with respect to a respective micro-lens of a second array of the pair of micro-lens arrays so that the micro-lenses of the second array produce in the far field an image of the respective micro-lens of the first array, wherein the micro-optical light mixer is characterized by an acceptance angle (α_acc) and a response function to a collimated light pulse transmitted within an acceptance angle (α_acc) having an angular profile showing a peak with a divergence angle (α1′) measured as full width at half maximum (FWHM) of the peak.

### Claim 7 (depends on 1)

The illumination device of claim 1, wherein the optical unit additionally comprises a bidimensionally extending channel structure comprising a plurality of side-by-side aligned channels.

### Claim 8 (depends on 7)

The illumination device of claim 7, wherein the side-by-side aligned channels are formed by void volumes separated by walls, wherein the walls separating the void volumes of the channels are made of or coated with a light absorbing material having an absorption coefficient for visible light greater than 70%.

### Claim 9 (depends on 7)

The illumination device of claim 7, wherein the side-by-side aligned channels are distributed adjacent to each other in a close-packing arrangement.

### Claim 10 (depends on 1)

The illumination device of claim 1, wherein the optical unit comprises at least one lateral surface extending transversal with respect to the first planar light mixing element and facing towards the inside of the optical unit, wherein each lateral surface is coated or made of a material with a reflectance factor η_r>70%.

### Claim 11 (depends on 10)

The illumination device of claim 10, wherein the at least one lateral surface abuts or overlaps the first planar light mixing element or a plane defined by an end of the plurality of side-by-side aligned channels facing the second light mixing element, and extends towards the second light mixing element.

### Claim 12 (depends on 1)

The illumination device of claim 1, wherein the collimated light source comprises an array of light-emitting devices each comprising a light emitter and at least one collimation lens illuminated by the light emitter, the light emitter being housed in a hollow housing which is at least partially made of or internally coated with light absorbing material having an absorption coefficient for visible light greater than 70%, and has at least an aperture where the at least one collimation lens is positioned.

### Claim 13 (depends on 12)

The illumination device of claim 12, wherein the collimated light source further comprises a channel structure positioned downstream of the array of light-emitting devices and upstream from the output surface, the channel structure being configured to transform a first collimated light beam featured by the presence of stray light emitted by the light-emitting devices and that impinges onto the channel structure into a second collimated light substantially free from stray light propagating at an angle higher than a cut angle (α_cut).

### Claim 14 (depends on 1)

The illumination device of claim 1, wherein:
the first planar light mixing element is characterized by a first response function having a first angular profile with a peak having a first divergence angle, and
the second planar light mixing element is characterized by a second response function having a second angular profile with a peak having a second divergence angle.

### Claim 15 (depends on 14)

The illumination device of claim 14, wherein the first divergence angle is measured as a full width at half maximum of the peak of the first angular profile and the second divergence angle is measured as a full width at half maximum of the peak of the second angular profile.

### Claim 16 (depends on 1)

The illumination device of claim 1, wherein the direct-light generator and the diffused-light generator cooperate to form outer light at the second emitting surface, the outer light comprising a first light component that propagates along directions contained within a narrow peak and a second light component that propagates along directions spaced apart from the narrow peak, the first light component having a correlated color temperature that is lower than a correlated color temperature of the second light component.

### Claim 17 (depends on 1)

The illumination device of claim 1, wherein illumination device is configured for generating natural light similar to that from the sun and sky, and the first light component has a CCT that is lower than a CCT of the second light component.

### Claim 18 (depends on 1)

The illumination device of claim 1, wherein the spatial modulation of the collimated light is greater than or equal to 0.5 mm and less than or equal to 30 mm.

### Claim 19 (depends on 1)

The illumination device of claim 1, wherein the spatial modulation of the collimated light is in a sub-millimeter range, and the first divergence angle is equal to or smaller than 20°.

### Claim 20

A sun-sky-imitating illumination device for generating natural light similar to that from the sun and the sky, the illumination device comprising:
a direct-light generator that comprises
a first emitting surface from which a direct light is emitted; and
a collimated light source configured to generate, from a primary light, a collimated light which exits an output surface positioned upstream from the first emitting surface with respect to a direct-light direction,
wherein the direct light has a luminance profile (Ldirect(x, y, θ, φ) which has a first peak in the angular distribution around the direct-light direction and the collimated light exiting the output surface has a luminance profile (Lcoll(x, y, θ, φ) which has a second peak in the angular distribution around the direct-light direction, the second peak being a narrow peak, and
a diffused-light generator that is at least partially light-transparent and is positioned downstream of the direct-light generator and comprises a second emitting surface and is configured to emit diffused light at the second emitting surface,
wherein the sun-sky-imitating illumination device is configured such that the direct-light generator and the diffused-light generator co-operate to form outer light at the second emitting surface which comprises a first light component which propagates along directions contained within the narrow peak and a second light component which propagates along directions spaced apart from the narrow peak,
wherein the first light component has a CCT which is lower than a CCT of the second light component,
wherein the direct-light generator comprises an optical unit positioned downstream of the output surface of the collimated light source and upstream from the first emitting surface with respect to the direct light direction, wherein the optical unit is configured to interact with the collimated light exiting the output surface to generate the direct light emitted from the first emitting surface so that the first peak of the luminance profile (Ldirect(x, y, θ, φ) of the direct light is larger than the second peak of the luminance profile (Lcoll(x, y, θ, φ) of the collimated light, the optical unit comprising
a first planar light mixing element characterized by a first response function having a first angular profile with a peak having a first divergence angle, the first planar light mixing element being positioned so as to at least partially intercept the collimated light exiting the output surface of the collimated light source and to define a unit input surface, and
a second planar light mixing element characterized by a second response function having a second angular profile with a peak having a second divergence angle, the second planar light mixing element being positioned downstream of the unit input surface so as to at least partially intercept the light crossing the unit input surface and to define a unit emitting surface,
wherein the first and second divergence angles are equal to or smaller than 40°, and
wherein the first and second planar light mixing elements are spaced apart from each other at least of a minimum unit depth (z1) measured along the direct light direction, configured to obtain uniform luminance of the direct light which exits the first emitting surface of the direct light generator,
wherein the collimated light source comprises an array of light-emitting devices each comprising a light emitter and at least one collimation lens illuminated by the light emitter, and each light-emitting device further comprises a pre-collimation lens positioned upstream from the collimation lens and substantially in contact with or proximal to the light emitter, the pre-collimation lens being configured to emit with a substantially angularly constant intensity within an emission cone, and to uniformly illuminate a whole light input surface of the collimation lens.

### Claim 21 (depends on 20)

The illumination device of claim 20, wherein the pre-collimation lens comprises a concave-curved light inlet surface facing the light emitter and a convex-curved light outlet surface.

### Claim 22 (depends on 21)

The illumination device of claim 21, wherein the concave-curved light inlet surface and the convex-curved light outlet surface have an aspheric profile.

### Claim 23

A direct-light generator of an illumination device, the direct-light generator comprising:
a first emitting surface;
a collimated light source configured to generate, from a primary light, a collimated light that exits an output surface positioned upstream from the first emitting surface with respect to a direct light direction; and
an optical unit positioned downstream of the output surface of the collimated light source and upstream from the first emitting surface with respect to the direct light direction, the optical unit comprising:
a first planar light mixing element defined by a first response function having a first angular profile with a peak having a first divergence angle, the first planar light mixing element being positioned so as to at least partially intercept the collimated light exiting the output surface of the collimated light source and to define a unit input surface, the first planar light mixing element comprising a low-angle white-light diffuser, and
a second planar light mixing element defined by a second response function having a second angular profile with a peak having a second divergence angle, the second planar light mixing element being positioned downstream of the unit input surface so as to at least partially intercept the light crossing the unit input surface and to define a unit emitting surface, the second planar light mixing element comprising a low-angle white-light diffuser,
wherein the first and second planar light mixing elements are spaced apart from each other by at least a minimum unit depth (z1) measured along the direct light direction such that the direct light that exits the first emitting surface of the direct light generator has a uniform luminance.

### Claim 24 (depends on 23)

The direct-light generator of claim 23, wherein the minimum unit depth (z1) is given by 5 cm≤z1≤50 cm.

### Claim 25 (depends on 23)

The direct-light generator of claim 23, wherein the low-angle white light diffuser is characterized by a response function having an angular profile with a peak having a divergence angle, the low-angle white light diffuser being configured to cause a blurring of the peak in the luminance profile (Lcoll (x, y, θ, φ) of the collimated light exiting the output surface.

### Claim 26 (depends on 23)

The direct-light generator of claim 23, wherein the low-angle white light diffuser of the second planar light mixing element is integrated in a diffused-light generator as a dispersion of transparent microparticles or a superficial random distribution of micro-refractors formed in at least one of a second emitting surface and a diffuser input surface of the diffused-light generator.

### Claim 27 (depends on 23)

The direct-light generator of claim 23, wherein the low-angle white-light diffuser of the first planar light mixing element is a micro-optical light mixer comprising a pair of micro-lens arrays, wherein each micro-lens of a first array of the pair of micro-lens arrays is positioned at a focal distance with respect to a respective micro-lens of a second array of the pair of micro-lens arrays so that the micro-lenses of the second array produce in the far field an image of the respective micro-lens of the first array, wherein the micro-optical light mixer is characterized by an acceptance angle (α_acc) and a response function to a collimated light pulse transmitted within an acceptance angle (α_acc) having an angular profile showing a peak with a divergence angle (α1′) measured as full width at half maximum (FWHM) of the peak.

### Claim 28 (depends on 23)

The direct-light generator of claim 23, wherein the optical unit additionally comprises a bidimensionally extending channel structure comprising a plurality of side-by-side aligned channels distributed adjacent to each other in a close-packing arrangement.

### Claim 29 (depends on 23)

The direct-light generator of claim 23, wherein the optical unit comprises at least one lateral surface extending transversal with respect to the first planar light mixing element and facing toward the inside of the optical unit, wherein each lateral surface is coated or made of a material with a reflectance factor η_r>70%.

### Claim 30 (depends on 29)

The direct-light generator of claim 29, wherein the at least one lateral surface abuts or overlaps the first planar light mixing element or a plane defined by an end of the plurality of side-by-side aligned channels facing the second light mixing element, and extends toward the second light mixing element.

### Claim 31 (depends on 23)

The direct-light generator of claim 23, wherein the first divergence angle is measured as a full width at half maximum of the peak of the first angular profile and the second divergence angle is measured as a full width at half maximum of the peak of the second angular profile.