FIELD OF THE INVENTION

The present invention relates to an arrangement for a window, for example suitable in a window or sky-light in a public area such as a shop. Furthermore, the invention relates to a window and a window lighting system.

BACKGROUND OF THE INVENTION

It is generally considered desirable to allow daylight into shops and galleries, for aesthetic as well as commercial reasons. Not only will the use of daylight for illumination save energy, and thus cost, but it has been shown that the positive effect on the atmosphere inside the shop will also increase sales. For this reason, windows and skylights (windows in the ceiling) are desired.

However, in regions with periods of dark climate, such as Northern Europe or

Canada, skylights and windows also create problems in shopping environments. Particularly during winter time and in the early morning, late afternoon, and evenings, the dark outside environment causes the window to appear as a dark surface (a "dark hole") which may give a feeling of insecurity. Even making the glass surface semi-translucent will not solve this problem, since the surface will still appear relatively dark.

Attempts have been made to replace windows with large area, LED-based luminaires providing daylight atmosphere. Although often successful from an aesthetic point of view, such solutions are typically expensive, and will not provide energy savings.

SUMMARY OF THE INVENTION

It is an object of the present invention to mitigate this problem, and to allow illumination by daylight less affected by the drawbacks discussed above.

According to a first aspect of the invention, this and other objects are achieved by an arrangement for a window located between an inside and an outside, said arrangement comprising a transparent light guide, arranged to be mounted on a window pane of the window, at least one light source, arranged to couple light into said light guide, out-coupling features cooperating with the light guide and arranged to out-couple light from the light guide towards the inside, an outside light sensor for detecting outside lighting conditions, and a controller connected to the sensor and the at least one light source, and programmed to adjust a light output from the light source based on the detected outside lighting conditions.

The controller is thus arranged to allow in-coupling of additional light into the light guide when the outside light (most typically daylight) is found to be insufficient for a satisfactory illumination on the inside.

A "window" is here intended to comprise any transparent section of a building structure, i.e. in outer walls, inner walls, ceiling, roof, floor, etc. The only relevant criterion is that the window separates two areas (labeled "inside" and "outside", and allows light to pass from the outside to the inside.

The "inside" is thus generally defined as the side of the window on which light can be out-coupled from the light guide, and the "outside" is the opposite side of the window. In other words, the expressions "inside" and "outside" do not imply that the window necessarily is arranged in the outer wall or roof of a building, and the window is not necessarily intended to allow daylight into a building. On the contrary, the window may be located e.g. in an inner wall between two rooms or areas, and the "outside" may simply be a different part of the building.

By controlling the light output of the light source, e.g. the intensity and color for the light source, the inside light output of the window can be modified. The inside light output of the window will include light from the outside, transmitted through the window (and light guide), as well as light from the light source, in-coupled into the light guide and out-coupled on the inside.

A window arrangement according to the present invention enables window/sky- light surfaces to be transparent during daylight conditions and illuminated during darker periods. This allows energy savings by allowing daylight to enter, and also avoids the window becoming a "dark hole". The present invention also enables improvement of the light intensity and/or color (e.g. color temperature Tc) of the inside light output of the window.

The intensity of the inside light output of the window can be selected to illuminate the interior of the space or to make the window like a decorative element during darkness outside. For example, the inside light output may be increased during grey, cloudy days with low levels of outside light levels, especially in winter time. This is particularly advantageous in the Northern countries such as Great Britain, the Netherlands, Germany, Scandinavia and Canada. Further, the color of the inside light output of the window can be modified. In this context, color can be a color temperature, a color near the blackbody line or a saturated color. Window arrangements according to the present invention may

advantageously be installed in homes as well as many commercial buildings, such as retail stores, supermarkets, shopping malls, gallerias, hotels, restaurants, public areas (train- stations, etc.). Further, an arrangement according to the invention may be integrated with a window at the time of manufacturing, or may be mounted to an already existing window.

According to one embodiment, the controller is programmed to control the luminance of the light source, to compensate a reduction in luminance detected by the outside sensor. For example, the controller may be programmed to activate the light source when the outside light falls below a predefined threshold. Such a solution requires no feedback, i.e. no information about inside lighting conditions.

According to another embodiment, the arrangement further comprises an inside light sensor for detecting inside lighting conditions, and the controller is programmed to adjust the light output based on the inside lighting conditions. For example, the controller can be programmed to control a color temperature of the light source, in order to adapt a color temperature of outside light transmitted through the window to match a color temperature of inside light detected by the inside light sensor.

An inside sensor also enables a more sophisticated control scheme, where the controller can adjust the light output based on feedback from the inside sensor, until desired inside lighting conditions are obtained.

The at least one light source is preferably a solid state light source, such as a LED. Solid state light sources are advantageous as they allow a large range of control algorithms, from instantaneous response (on a time scale of seconds) to a delayed response (time scale of minutes).

According to a second aspect, the invention relates to a window provided with a light guide of the arrangement according to the first aspect of the invention. The invention also relates to a complete system comprising a window and an arrangement according to the first aspect.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention. Figure 1 schematically shows a window provided with a window arrangement according to an embodiment of the present invention.

Figures 2a and 2b show a top view and a side view of some parts of the window arrangement in figure 1 in more detail.

DETAILED DESCRIPTION

In figure 1, a window 1 has been provided with an arrangement according to an embodiment of the present invention. The arrangement comprises color mixing layer in the form of a light guide 2 which is fitted to the window pane 3 of the window 1 and covers essentially the entire window pane. The light guide 2 should have high transparency and may be made of glass or a highly transparent plastic such as Perspex (PMMA). A suitable thickness for the light guide is 1-2 mm, but other thicknesses are also possible. The light guide may have a rectangular, hexagonal or even freeform shape.

A plurality of light sources 4 arranged in connection to the light guide, and may be arranged along one edge of the light guide, along two opposite edges (as illustrated in figure 1) or along all edges of the light- guide 2. The light guide 2 and light sources 4 are arranged in such a way that light from the light sources can be in-coupled into the light guide 2. The light sources 4 may be solid state light sources, such as light emitting diodes (LED). In the illustrated example, the light sources include red, green and blue LEDs, so as to enable generation of light of any color.

The light guide is formed to enable light coupled into the light guide to be guided by total internal reflection (TIR). In order to out-couple light from the light guide 2, the light guide 2 is provided with out-coupling features 5, typically adapted to cause refraction of light so that the light no longer fulfills the conditions for total internal reflection and escapes the light guide 2.

The out-coupling features may comprise structures formed in the light guide surface on one or both sides of the light guide. Such out-coupling structures may be local roughness made by sandblasting, or may be areas with a diffractive structure, such as grooves, ridges, or wedges. The features may also comprise refractive particles embedded in the light guide material. Further, the features may be a pattern of spots or dots of a suitable surface coating applied on one or both sides of the light guide 2 e.g. by silk- screening. If the surface coating spots are thick enough, they will diffusely reflect almost all light. This means that all light can be coupled out in the desired direction. Also, light coupled out of the light- guide in this manner has an almost Lambertian distribution, and by having the proper spatial distribution of the out-coupling dots, the light out-coupled from the light guide 2 can be essentially uniform. In practice, this means a dense pattern of dots far away from the LEDs 4 and a less dense pattern close to the LEDs 4. The surface coating may be e.g. white paint. It may also be phosphor, e.g. tuned to convert blue light travelling inside the light-guide into yellow light, so that the remainder of the blue light together with the yellow light will give the impression of white light. In this manner a more light-efficient system may be obtained.

The arrangement further comprises a controller 6 connected to the light sources and arranged to control the light output of the light sources. An outside sensor 7 is located on the outside of the window, and is connected to the controller 6 and arranged to provide information about outside lighting conditions, e.g. intensity and color temperature of daylight in the case of a window facing an outdoor environment.

The arrangement may also comprise an inside sensor 8, located on the inside of the window, and connected to the controller 6 and arranged to provide information about inside lighting conditions.

In operation, the controller 6 receives a sensor signal from the outside sensor

7, and based on this input calculates a required illumination of the color mixing layer to obtain the desired color and intensity of light emitted to the inside of the window. Note that the light emitted to the inside typically contains light transmitted from the outside through the window and light guide, as well as light from the light sources 4, in-coupled into the light guide and out-coupled by the out-coupling features 5.

In order to determine a required light output, the well-known color addition theory may be used, together with a predefined set point for the color of inside illumination. If the predefined set point cannot be reached, the closest possible color and intensity is used, with color typically being the primary target.

During daylight conditions different color and intensity set points may be used compared to during dark conditions (dusk and dawn, night). Daylight conditions can be defined e.g. by intensities measured in [Lux] and color temperatures in [K] above certain threshold values. The threshold values can be factory pre-set or set during installation.

If an inside sensor 8 is connected to the controller 6, a more sophisticated control scheme including feedback of inside lighting conditions may be applied. This enables a more precise regulation of the inside lighting conditions, adaptively responsive not only to outside lighting conditions but also to changing inside illumination, such as artificial lighting etc. Figures 2a and 2b show an embodiment of how light can be in-coupled and out-coupled in a semi-transparent emissive light guide 2.

Light sources, here LEDs 4, are arranged in diamond shaped recessions or holes 10 in the light guide 2. The LEDs may include LEDs of various colors, for example red, green and blue LEDs, to provide a color-adaptable emissive window. Here, top-emitting LEDs 4 are used, and a conical or pyramid shaped reflecting element 11 fitted in the hole 10 in order to direct light from the LED 4 sideways thereby in-coupling it into the light guide 2. The diamond shape of the hole 10 ensures that the light of each LED 4 is quickly mixed with that of neighboring LEDs (that may emit different colors). The edges of the light guide 2 may be provided with reflecting surfaces 13 to ensure no light is inadvertently lost.

A pattern of spots or dots 12 is provided on the surface 2a of the light guide 2 facing the outside. Light 13 in the light guide that is incident on one of the spots 12 will be refracted, so that the conditions for total internal reflection are no longer met, and light 14 will then be out-coupled through the surface 2b facing the inside. The spots 12 do not need to cover more than 10% of the light guide surface, probably even less, so that the transparency of the light guide, and hence the entire window provided with an arrangement according to this embodiment of the invention, can be high.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, other materials and dimensions may be used for the light guide, and other types of out-coupling means may be employed. Also, more sophisticated control schemes may be used to control the arrangement, possibly including other types and differently located sensors.