Sun-sky-imitating illumination device

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.

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.