EP4649262A1

EP4649262A1 - An artificial skylight

Info

Publication number: EP4649262A1
Application number: EP23833150.8A
Authority: EP
Inventors: Ties Van Bommel; Martinus Hermanus Wilhelmus Maria Van Delden; Alexander Henricus Waltherus VAN EEUWIJK
Original assignee: Signify Holding BV
Current assignee: Signify Holding BV
Priority date: 2023-01-09
Filing date: 2023-12-20
Publication date: 2025-11-19
Also published as: WO2024149592A1; CN120418579A; JP2025542559A

Abstract

An artificial skylight comprising a light source surrounded by a protruding rim. An outermost exposed portion of the protruding rim is smaller than an innermost exposed portion of the protruding rim. The outermost exposed portion of the protruding rim is non-zero.

Description

An artificial skylight

FIELD OF THE INVENTION

The present invention relates to the field of artificial skylights.

BACKGROUND OF THE INVENTION

The beneficial properties of daylight on human and animal well-being is well documented. However, an increasing proportion of the population spends most of their time indoors. Although skylights and windows offer the opportunity to provide daylight to an indoor environment, these can only be placed at or near the boundaries of a building, and cannot typically illuminate a center of the building.

One technique to address this issue is to make use of artificial skylights, which simulate or resemble true skylights (sometimes called natural skylights) in simulating daylight within an indoor environment. However, it has been recognized that the beneficial effect of artificial skylights is negatively impacted if the artificial skylight has an unnatural appearance, such that a viewer of the artificial skylight does not perceive it to be or resemble a true skylight.

There is therefore a desire to provide an improved artificial skylight that is perceived, by a viewer, to be more similar to a true skylight.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided an artificial skylight comprising: a light source configured to output, as light source light, light through a light exit window, the light source having a first thickness; a protruding rim surrounding the light source and having: an inner side surface that is proximate to the light source and has an exposed portion of a first length; an outer side surface that is more distant from the light source than the inner side surface and has an exposed portion of a second length; and a front surface connecting the inner side surface to the outer side surface; wherein the first length is greater than the second length and the second length is greater than Proposed embodiments provide an artificial skylight in which the light source is perceived as being recessed to a greater extent with respect to the inner side surface than to the outer side surface. This causes a viewer of the artificial skylight (when it is mounted to the ceiling) to perceive the light source as being located beyond the ceiling, thereby more closely resembling a true skylight.

In particular, when the artificial skylight is mounted to a ceiling, the viewer will perceive the overall extent of the artificial skylight to protrude outwardly from the ceiling by the second length. If the first length is greater than the second length, then the light source will be perceived as being recessed into, or positioned beyond, the ceiling in the manner of a real skylight.

The artificial skylight may be configured wherein, when mounted to a flat surface, the inner side surface and the outer side surface are substantially perpendicular to the flat surface. This approach enhances the perception that the light source is located beyond the ceiling to a viewer of the artificial skylight.

In some examples, the rim is shaped as a (circular) ring. However, the rim may be arranged in other ring shapes and/or structure, e.g., a polygonal structure such as a rectangular structure.

In some examples, the second length is less than the first thickness. This creates or facilitates a relatively high ratio between the first and second lengths, enhancing the effect of the perception that the light source is located beyond the ceiling to a viewer of the artificial skylight.

In other examples, the second length is greater than the first thickness. This results in a light source that is perceived as being arranged more recessed with respect to the outer side surface, enhancing the effect of the perception that the light source is located beyond the ceiling to a viewer of the artificial skylight.

The first length may be greater than or equal to 1.2 times the second length, e.g., greater than or equal to 1.5 times the second length, e.g., greater than or equal 2 times the second length. This creates a sufficiently large perceived depth for viewers located at larger distances from the artificial skylight.

The first thickness may be less than 5 mm, preferably less than 3 mm, more preferably less than 2 mm, most preferably less than 1 mm. This embodiment provides a slim, plate shaped, flat light source, with a light exit window extending in a virtual plane and reducing a noticeability of the light source of being unnatural to a viewer of the artificial skylight. Typically, the inner side surface and the outer side surface are substantially perpendicular to said major light exit window (hence to said virtual plane). Such a slim light source also allows creating a larger first length, enhancing the effect of the perception to a viewer of the artificial skylight that the light source is located beyond the ceiling, or in other words that the light source is natural light coming from a location beyond the ceiling.

In some examples, an angle between the front surface and a plane perpendicular to the outer side surface is from 2° to 15°, and preferably from 2° to 12°, more preferably 4° to 10°. Inclining the front surface at these angles reduces the visibility of the inclination to a viewer of the artificial skylight. This further enhances the perception that the light source is located beyond the ceiling, as the inclination reduces the likelihood that the viewer understanding or realizing that the first length is greater than the second length.

Optionally, the first length is no less than 4 mm, preferably no less than 6 mm, more preferably no less than 7 mm, most preferably no less than 9 mm. This further enhances the perception that the light source is located beyond the ceiling.

In some examples, the distance between the inner side surface and the outer side surface is no less than 40mm, preferably no less than 60 mm.

In some examples, the aperture of the light exit window of the light source has a width that is no less than two times the distance between the inner side surface and the outer side surface, e.g., no less than 3 times this distance, e.g., no less than 5 times this distance.

Optionally, the exposed portion of the inner side surface is yellow. This coloring causes the inner side surface to absorb blue light and provide yellow light, more closely resembling the output of a true skylight.

In some examples, the exposed portion of the inner side surface is configured to emit or reflect further light having a Correlated Color Temperature of at least 500 K lower than a Correlated Color Temperature of the light source light. This enhances the effect that the light source light is natural light.

In some examples, the outer side surface is also configured to emit light having a different Correlated Color Temperature to that of the light source light. This enhances the effect that the light source light is natural light.

In some examples, the reflectivity of the exposed portion of the outer side surface is lower than the reflectivity of the exposed portion of the inner side surface. This approach effectively simulates a brighter color at the inner side surface, more closely resembling the effect of light provided by a non-artificial skylight.

The difference in reflectivity may be at least 30%, e.g., at least 50%. The color of the exposed portion of the outer side surface may be darker than the exposed portion of the inner side surface. This causes an optical effect that the inner side surface has been illuminated by natural light, increasing the resemblance of the artificial skylight to a natural/true skylight.

Optionally, the surface roughness of the front surface is greater than the surface roughness of the inner side surface and/or the outer side surface. This provides a greater contrast with the side surface(s), to enhance the apparent recession of the light source with respect to a surface to which the artificial skylight is mounted.

In some examples, the artificial skylight is configured such that when it is mounted on/to a flat surface, the outer side surface is spaced apart from the flat surface by a gap of no less than 2 mm. This provides another technique for reducing the length of the exposed portion of the outer side surface relative to the exposed portion of the inner side surface, to further enhance the optical effect that causes the light source to be perceived as being located in/beyond the flat surface.

In some examples, the gap is no greater than 10 mm, e.g., no greater than 5 mm. This reduces the likelihood that a viewer of the artificial skylight will identify/perceive the gap.

In some examples, the light source light has a Correlated Color Temperature of no less than 6000K. This causes the emitted light to more closely resemble that of natural light, thereby increasing a resemblance between the artificial skylight and a true/natural skylight.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Fig. I illustrates an artificial skylight;

Fig. 2 illustrates another artificial skylight;

Fig. 3 illustrates yet another artificial skylight;

Fig. 4 provides a bottom-up view of an artificial skylight.

DETAILED DESCRIPTION OF THE EMBODIMENTS The invention will be described with reference to the Figures.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

The invention provides an artificial skylight. The artificial skylight comprises a light source surrounded by a protruding rim. An outermost exposed portion of the protruding rim is smaller than an innermost exposed portion of the protruding rim. The outermost exposed portion of the protruding rim is non-zero.

The present disclosure recognizes that configuring the exposed portion of an outer side surface of a rim (surrounding a light source) to be smaller than an inner side surface of the rim results in an optical effect that the light source is located within or beyond a flat surface on which the artificial skylight is mounted. This effect can be exploited to configure an artificial skylight to more closely resemble a true/natural skylight.

Embodiments can be employed in any suitable environment in which it would be beneficial to have artificial skylights, e.g., office, home, clinical and/or industrial environments.

Figure 1 is a cross-sectional view of an artificial skylight 100 according to an embodiment. For illustrative clarity, the artificial skylight is illustrated as being mounted on a flat surface 190, such as a ceiling or wall.

The artificial skylight 100 comprises a light source 110 having a first thickness T. The term “first thickness” is here used to avoid any ambiguity when later referring to the thickness of the light source (which can instead be referred to as the “first thickness”).

In the context of the present invention, a light source 110 is a module or component that emits or outputs light out of a light output window 111. The light output through the light output window can be labelled light source light.

The light source may, for instance, be a light guide panel (e.g. comprising a light guide arranged between a reflector and a diffuser) or a shallow light mixing chamber. Thus, although possible, the light source does not need to itself generate light, but may simply guide generated light out of a light exit window 111. Preferably, the light for/of the light source is generated by one or more light emitting elements such as light emitting diodes (LEDs). The light emitting element(s) may be positioned within the light source itself, or to one or more sides of the light source (e.g., which guides and/or mixes the light for outputting at a light output window).

The artificial skylight 100 also comprises a protruding rim 120 that surrounds the light source. The protruding rim protrudes or extends from the flat surface 190 (when the skylight 100 is mounted on the flat surface) more than the light source.

The protruding rim 120 is defined by or comprises an inner side surface 121, an outer side surface 122 and a front surface 123. The inner side surface 121 is more proximate to the light source 110 than the outer side surface 121 (e.g., is the most proximate surface of the protruding rim to the light source). The outer side surface 122 is more distant from the light source 110 than the inner side surface 121. The front surface 123 connects the inner side surface to the outer side surface. When the artificial skylight 100 is mounted on the flat surface 190, as illustrated in Figure 1, the front surface is the most distant surface of the protruding rim from the flat surface 190.

Of course, the protruding rim 120 may comprise a rear surface 124 that also coupled the inner side surface to the outer side surface. The rear surface 124 is, when the skylight is mounted to the flat surface 190, more proximate to the flat surface than the front surface. In normal use, the rear surface 124 is at least partially concealed from a view of an observer of the artificial skylight.

The inner side surface 121 has an exposed portion 121 A of a first length LI. The exposed portion 121 A is an uncovered region or area of the inner side surface, e.g., a part of the inner side surface that is not covered or concealed by the light source 110.

The outer side surface 122 also has an exposed portion, which is of a second length L2. The second length L2 is non-zero, i.e., greater than 0 mm.

In general, an exposed portion is a portion that is visible or viewable to an observer of the artificial skylight 100 when the skylight is installed on a flat surface 190 in normal operation (e.g., without having to disassemble the skylight).

Both the inner 121 and outer 122 side surfaces extend outwardly from the flat surface 190, when the artificial skylight 100 is mounted to the flat surface 190. In some preferred examples, when the artificial skylight 100 is mounted to a/the flat surface 190, the inner side surface 121 and the outer side surface 122 are substantially perpendicular to the flat surface 190. The first length LI is configured to be larger than the second length L2. Thus, the first length LI is also non-zero.

This results in an optical illusion to a viewer of the artificial skylight 100 that the light source 110 is embedded within the flat surface 190 or located beyond the flat surface. This causes the viewer to perceive the light source 110 as not originating from an artificial light source mounted to the flat surface, but rather light transmitted from a more distance source (i.e., in the manner of a true skylight).

In particular, the proposed configuration causes a viewer of the artificial skylight to perceive a depth at an interior of the artificial skylight, resembling or simulating the appearance of a natural or true skylight.

The artificial skylight 100 thereby has a more natural appearance than existing or previous artificial skylights.

This effect is enhanced for greater differences between the first and second lengths.

For instance, the first length LI may be greater than or equal to 1.2 times the second length L2 to create a larger perceived depth for viewers located at a distance from the artificial skylight.

As another example, the first length LI may be greater than or equal to 1.5 times the second length L2, e.g., greater than or equal 2 times the second length L2. These approaches further enhance the effect provided by the difference between the first length LI and the second length L2.

In some examples, the first length LI is greater than the second length L2 and the first thickness T is less than the second length L2. This causes the light source 110 (when the artificial skylight is mounted to a flat surface) to extend outwardly from the flat surface to a lesser extent than the outer side surface 122, i.e., such that the light source is recessed with respect to the outer side surface 122.

In other examples, the first length LI is greater than the second length L2 and the first thickness T is greater than the second length. This facilitates an increase in the ratio between the first and second lengths, and thereby a greater perceived recession of the light source.

If, when the skylight 100 is mounted to the flat surface 190, there is no gap between the inner side surface 121 and the flat surface 190 and no gap between the outer side surface 122 and the flat surface 190, then the difference in size of the first and second lengths will result in the front surface being inclined with respect to the flat surface. If the inclination of the front surface 123 is sufficiently small, then a viewer of the artificial skylight 100 will (at a distance) not perceive or have a reduced perception of the inclination. This enhances the optical effect of the light source 110 appearing to be located beyond the flat surface 190. In particular, the skilled person will perceive the inner 121 and outer 122 side surface to terminate at a same distance from the flat surface 190, such that the additional length of the exposed portion 121 A of the inner side surface 121 compared to that of the outer side surface 122 is perceived to extend into the flat surface 190.

Accordingly, to achieve this goal, the angle 0 between the front surface 123 and a plane 130 perpendicular to the outer side surface 122 may be less than 15°, e.g., less than 12°. Even more preferably, the angle 9 is less than 10°.

To achieve sufficient difference between the length of LI and L2 to realize the optical effect, it is preferable that the angle 9 is no less than 2°.

Preferably, the first length LI is no less than 4 mm, e.g., no less than 10 mm.

In preferred examples, the distance D between the inner side surface and the outer side surface is no less than 40 mm and preferably no less than 60 mm. It will be apparent that the length of the front surface 123 is dependent upon the distance D.

The aperture of the light exit window 111 of the light source 110 may have a width W. The width W of this aperture is preferably no less than 2 times the distance D between the inner side surface and the outer side surface.

Table 1 illustrates a relationship between the value of the angle 9 and the perceptibility of inclination/depth.

A perceptibility of inclination indicates how perceptible the angle 9 is to a viewer of the artificial skylight under normal viewing conditions. This is graded on a categorical scale of: " indicates Very Low Perceptibility; indicates Low Perceptibility;; “+” indicates Medium to High Perceptibility; and “++” indicates High to Very High Perceptibility.

A perceptibility of depth is an indicator of the effectives of the optical effect that the light source is positioned within or beyond the flat structure relative to the mounting position against the flat structure, protruding rim. This is also graded on a categorical scale of: " indicates Very Low Perceptibility; indicates Low Perceptibility;; “+” indicates Medium to High Perceptibility; and “++” indicates High to Very High Perceptibility.

For the purposes of Table 1, the distance D is fixed (e.g., at 50 mm), the value of L2 is fixed (e.g., at 5 mm), and the value of LI changes accordingly with the changes in the angle 9. The results of Table 1 were produced in experimental conditions that assessed the average perceptibility of the inclination and depth for a plurality of sample observers.

Angle Perceptibility of Inclination Perceptibility of Depth 9 (°)

1

2 - +

3 - +

4 - ++

5 - ++

6 - ++

7 - ++

8 - ++

9 - ++

10 - ++

11 - ++

12 - ++

13 + ++

14 + ++

15 + ++ TABLE 1

Table 1 clearly indicates that an angle in the range of from 2° to 15° provides a good balance of inclination and depth perceptibility, with an angle of between 4° to 10° providing a particularly advantageous balance of inclination and depth perceptibility. Table 1 also indicates that an angle less than 2° does not provide the desired effect of depth perceptibility, and is thereby less preferable.

Preferably, when the artificial skylight 100 is mounted to the flat surface 190, the light source 110 abuts the flat surface 190. This further reduces a perceived profile of the light source, emulating a natural or true skylight. Figure 2 illustrates an alternative artificial skylight 200.

In a similar manner to the previously described artificial skylight 100, the artificial skylight 200 comprises a light source 210 and a protruding rim 220. The protruding rim 220 again comprises an inner side surface 221, an outer side surface 222 and a front surface 223.

The artificial skylight 200 differs from the previously described artificial skylight 100 in that the protruding rim 220 is configured such that, when the artificial skylight 200 is mounted to a flat surface 190, the outer side surface 222 is spaced apart from the flat surface 190 by a gap G. Thus, a gap G is formed between the outer side surface 222 and the flat surface 190.

The presence of the gap reduces the size of the second length L2 (of the exposed portion of the outer side surface). This further enhances the optical effect that causes a viewer of the artificial skylight to perceive the light source 210 as being located in/beyond the flat surface on which the skylight 200 is mounted.

To a viewer of artificial skylight 200, a suitably sized gap G will either be imperceptible or difficult to ascertain or perceive the precise size of the gap.

In some examples, the gap G is no greater than 10 mm, e.g., no greater than 5 mm. This reduces the likelihood that a viewer of the artificial skylight will identify/perceive the gap.

The gap may be larger than 2 mm, e.g., larger than 3 mm. This approach enhances the optical effect of the light source being beyond in/beyond the flat surface 190.

Any optional feature or characteristics of the previously described artificial skylight can be implemented in the artificial skylight 200.

Figure 3 illustrates another artificial skylight 300.

In a similar manner to the previously described artificial skylight 200, the artificial skylight 300 comprises a light source 310 and a protruding rim 320. The protruding rim 320 again comprises an inner side surface 321, an outer side surface 322 and a front surface 323.

The artificial skylight 300 differs from the alternative artificial skylight 200 previously described in that the front surface 323 is not inclined with respect to the flat surface 190 and/or a plane perpendicular to the outer side surface 322. This approach makes use of only the gap G in order to cause the length LI of the exposed portion of the inner side surface 321 to be greater than the length L2 of the exposed portion of the outer side surface 322.

Any optional feature or characteristics of any previously described artificial skylight can be implemented in the artificial skylight 300. Figure 4 illustrates an artificial skylight 400, mounted to a flat surface 190, according to an embodiment. In particular, Figure 4 provides a bottom-up view of the artificial skylight 400.

The artificial skylight 400 comprises a light source 410 and a protruding rim 420. The light source 410 is entirely surrounded or bounded by the protruding rim 420.

In the illustrated example, the protruding rim 420 is shaped as a ring or annulus, with the light source having a corresponding circular or cylindrical shape.

The cross-sectional shape of the artificial skylight 400 may be embodied as any previously described artificial skylight, e.g., any artificial skylight as described with reference to any of Figures 1 to 4.

Further optional features of an artificial skylight, more specifically the protruding rim of an artificial skylight, are hereafter described. These optional features can be implemented in any herein described embodiment of an artificial skylight to advantage.

In at least one example, the exposed portion of the inner side surface is yellow. This coloring causes the inner side surface to absorb blue light and provide yellow light, more closely resembling the output of a true or natural skylight.

In some examples, the exposed portion of the inner side surface is configured to emit or reflect further light having a Correlated Color Temperature of at least 500K lower than a Correlated Color Temperature of the light source light. This enhances the effect that the light source light is natural light.

Thus, the inner side surface and/or the outer side surface may each comprise one or more light emitting devices, e.g., light emitting diodes, for generating and emitting light.

In some examples, the color or shade of the exposed portion of the outer side surface is darker than the exposed portion of the inner side surface. In some examples, the reflectivity of the exposed portion of the outer side surface is lower than the reflectivity of the exposed portion of the inner side surface.

Both of these approaches cause the inner side surface to appear to have an enhanced lamination compared to the outer side surface, causing the perception that the inner side surface has been illuminated with natural light, increasing a resemblance of the artificial skylight with a natural/true skylight. This effect is enhanced if the outer side surface and the inner side surface are the same color (e.g., yellow), but different shades thereof.

In some examples, the front surface has a color or reflectivity that gradually changes from a first color/reflectivity (closest to the inner side surface) to a second color/reflectivity (closest to the outer side surface). If used, the first color is lighter than the second color. If used, the first reflectivity is greater than the second reflectivity. This also causes a perception that the side closest to the inner side surface has been illuminated, e.g., with natural light. This enhances the perception that the artificial skylight is a natural/true skylight, i.e., increasing a resemblance of the artificial skylight with a natural/true skylight.

In some examples, the front surface has a greater surface roughness Ra than at least the inner side surface (and optionally the outer side surface). This causes the inner side surface to reflect more light than the front surface, resulting in the inner side surface appearing to be more completely illuminated by natural light. This enhances the perception that the artificial skylight is a natural/true skylight, i.e., increasing a resemblance of the artificial skylight with a natural/true skylight.

Above-described embodiments of an artificial skylight make use of a light source. A number of optional, but advantageous, features for such a light source are hereafter described, and can be implemented in any herein described embodiment of the artificial skylight.

In some examples, the thickness T of the light source is less than 10 mm, and more preferably less than 5 mm. This provides a slim light source that further reduces the noticeability or perceptibility of the light source to a viewer or observer of the artificial skylight. Thus, it is preferable for the thickness T of the light source to be as thin as possible.

In some examples, the light source is configured to generate light having a Correlated Color Temperature of no less than 6,000 K. More specifically, the light source is preferably configured to be capable of generating light having a CCT of no less than 6,000 K. This more closely simulates natural light, thereby more closely aligning the perceived appearance of the artificial skylight with that of a natural/true skylight.

Of course, the light source may be configured such that the Correlated Color Temperature (CCT) of the light source light can be controlled and/or changed. For instance, the Correlated Color Temperature may be variable within a predetermined range, e.g., responsive to a user input. A suitable example of a predetermined range is a range of from 1,800 K to 20,000 K. Example lights sources capable of such emitting light in such a range are well-established in the art. The light source may have a diameter or width of no less than 0.1 m, e.g., no less than 0.2 m. In some examples, the light source has a diameter or width of no more than 2 m, e.g., no more than Im. For instance, the light source may have a diameter of between 0.1 m and 1 m. It has been identified that the optical effect of the present invention is observed for at least light sources having these sizes.

It will be appreciated that any herein described artificial skylight may comprise additional electronic/circuitry components, e.g., for powering, driving and/or controlling the light source of the artificial skylight. Preferably, any such electronic component are at least partially integrated or housed within the protruding rim. This technique helps to cover or conceal the components, such that the artificial skylight more closely resembles a natural/true skylight.

Similarly, the light source may be associated with one or more light emitting elements (e.g., one or more LEDs). The one or more light emitting elements may be positioned as part of the light source itself, or externally to the light source that is configured to receive the emitted light and redirect received light out of the light exit window.

The one or more light emitting elements may be at least partially housed within the protruding rim, but positioned such that light is provided to the light source for outward emission via a light exit window. Alternatively, the one or more light emitting elements may be entirely housed within the light source itself, i.e., the light source may generate the light that is emitted out of the light exit window.

The artificial skylight may comprise one or more mounting components for mounting the artificial skylight to a flat surface. Suitable mounting components are well known in the art, including screws, nails, clipping elements, adhesive (e.g., glue) or other similar products that are capable of mounting and supporting an artificial skylight to/against a flat surface such as a ceiling or wall.

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.

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.

If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa.

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

Claims

CLAIMS:

1. An artificial skylight (100) comprising: a light source (110) configured to output, as light source light, light through a light exit window (111), the light source having a first thickness (T); a protruding rim (120) surrounding the light source and having: an inner side surface (121) that is proximate to the light source and has an exposed portion of a first length (LI); an outer side surface (122) that is more distant from the light source than the inner side surface and has an exposed portion of a second length (L2); and a front surface (123) connecting the inner side surface to the outer side surface; wherein the first length (LI) is greater than the second length (L2) and the second length (L2) is greater than 0 mm, and wherein an angle (9) between the front surface (123) and a plane perpendicular to the outer side surface (122) is from 2° to 15°, and preferably from 2° to 12°.

2. The artificial skylight of claim 1, wherein, when mounted to a flat surface (190), the inner side surface (121) and the outer side surface (122) are substantially perpendicular to the flat surface.

3. The artificial skylight of claim 1 or 2, wherein the rim is shaped as a ring.

4. The artificial skylight of any of claims 1 to 3, wherein the second length (L2) is less than the first thickness (T).

5. The artificial skylight of any of claims 1 to 3, wherein the second length (L2) is greater than the first thickness (T).

6. The artificial skylight of any of claims 1 to 5, wherein the first length (LI) is greater than or equal to 1.5 times the second length (L2).

7. The artificial skylight of any of claims 1 to 6, wherein the first thickness (T) is less than 5 mm.

8. The artificial skylight of any of claims 1 to 7, wherein the first length (LI) is no less than 4 mm.

9. The artificial skylight of any of claims 1 to 8, wherein the distance (D) between the inner side surface and the outer side surface is no less than 40 mm, and wherein an aperture of a light exit window of the light source has a width (W) being no less than two times the distance (D) between the inner side surface and the outer side surface.

10. The artificial skylight of any of claims 1 to 9, wherein the exposed portion of the inner side surface is (i) yellow and/or (ii) configured to emit or reflect further light having a Correlated Color Temperature of at least 500 K lower than a Correlated Color Temperature of the light source light.

11. The artificial skylight of any of claims 1 to 10, wherein the reflectivity of the exposed portion of the outer side surface is lower than the reflectivity of the exposed portion of the inner side surface.

12. The artificial skylight of any of claims 1 to 11, wherein the exposed portion of the outer side surface has a color that is darker than the exposed portion of the inner side surface.

13. The artificial skylight of any of claims 1 to 12, wherein the surface roughness of the front surface is greater than the surface roughness of the inner side surface and/or the outer side surface.

14. The artificial skylight of any of claims 1 to 13, wherein, when mounted to a flat surface (190), the outer side surface is spaced apart from the flat surface by a gap (G) of no less than 2 mm, optionally wherein the gap is no greater than 10 mm.

15. The artificial skylight of any of claims 1 to 14, wherein the light source light has a Correlated Color Temperature of no less than 6000 K.