A system and method for blocking light

Abstract

 A system (1) and method serves for blocking light or thermal energy passing through an opening (3). The light-blocking system (1) comprises a length-adjustable screen (5) having a first face (12a) and a second face (12b) interconnected at a distance from each other by means of a spacer means (14), a frame (2) bordering at least a part of the opening (3), and means for blocking light passing through a gap between at least one lateral edge (16) of the length-adjustable screen (5) and the frame (2), which means for blocking light passing through said gap comprises at least one slot (17) extending inside the length-adjustable screen (5) between the first plane (13a) and the second plane (13b) from at least one free lateral edge (16) of the length-adjustable screen (5), and a longitudinal key means (6) protruding from the frame (2) inside the opening (3) opposite the at least one slot (17) and configured to engage said at least one slot (17). The key means and the slots engages to prevent passing of light as well as light reflections does not occur.

Description

[0001] The present invention relates to a system for blocking light and/or thermal energy passing through an opening, the light-blocking system comprises

• a length-adjustable screen of the kind that has a first face defining a first plane opposite a second face defining an opposite second plane,
• which first face and second face are interconnected at a distance from each other by means of a spacer means,
• a frame bordering at least a part of the opening, and
• means for blocking light passing through a gap between at least one lateral edge of the length-adjustable screen and the frame.

[0002] Light-blocking structures, such as light-blocking curtains, blackout curtains or dark drapes, are commonly used to screen openings such as windows for incoming light.

[0003] People that work at night may for example need to sleep at day without being hampered by daytime light. Another advantage of light-blocking curtains is that they can keep a room from warming up during hot days and help keep a room warm during cold days. Thus light-blocking curtains provide insulation, and their use may save money and energy.

[0004] Screening light is for example needed at offices, cinemas, theatres and private homes during events like showing films and slideshows, viewing television, displaying presentations involving light sources, and similar performances and actions.

[0005] Light-blocking curtains aims to block 100% of incoming light. To that aspect the common problem is to achieve a good fit of standard light-blocking curtains into the opening in a manner that does not leaves gaps or light paths between the frame bordering the light incoming opening and free edges of the light-blocking curtain.

[0006] Early days light-blocking curtains were simply a dark or black roller shade or drape, where light easily could pass between window frame and curtain due to bad fit. To be able to roll up roller shades they are always made narrower than the width of the opening, which inevitable results in light gaps on each side of the roller shade. The only way is to mount the roller shade outside the opening instead of fitting it fully recessed into the window opening.

[0007] More modern and better light-blocking solutions have been provided since early days roller shades.

[0008] In the following description the term "light-blocking structure" is used for all kinds of screens, drapes or curtains. Where appropriate these terms may are used for interrelated structures and can be mutually substituted.

[0009] An example of an improved light-blocking curtain is disclosed in European patent no. 379242 in form of a double-walled curtain of pleated material. Folds of pleated material of one curtain wall is connected by means of two parallel connecting strips to folds of an opposite facing curtain wall, to form a combined curtain module. The module can be extruded so that the height and width of the curtain module can be determined in a simple manner, e.g. as tubular and endless length of material from which a suitable piece can be cut to make the final light-blocking curtain.

[0010] US patent no. 4,019,554 discloses a thermal insulating curtain comprising a plurality of superimposed uni-directionally arranged tubular members with a common slat-like partition between each two adjacent ones of said tubular members. Each of these tubular members along its two opposite sides has a folding crease to allow collapsing of said tubular members to thereby permit collapsing of the entire curtain in a manner of blind or to roll the curtain up in the manner of a shade.

[0011] US patent no. 4,984,617 discloses a pleated curtain of the expansible-collapsible type. The curtain has multicellular structure and may serve as a Venetian blind for controlling light diffusing through the curtain.

[0012] The problem however still remains that the lateral gap between the window frame and the exterior free edges of known black-out curtains is difficult to close effectively and allows light to pass.

[0013] The common solution to this problem is to cover the gap using a profile protruding from the frame bordering the opening. The profile overlaps a longitudinal area of at least one exterior face of the curtain. Typically such a profile is U-shaped or L-shaped. In case of a U-profile the curtain runs between the legs of. Thus the legs of the U, or the L are always exterior to the curtain and some light is still able to pierce the darkness via the relatively open free path between curtain and profile. The problem also exists that window openings often are out of square, in particular in old buildings. As a result the fit of a standard light-blocking curtain is often bad. Furthermore incident light is reflected by the exterior surface of the U-profile or L-profile.

[0014] Another huge problem when using L-profiles are that the curtain can flutter, e.g. if somebody opens a door in the room or the window is open. Such fluttering results in very annoying and uncontrollable uncovering of light-incoming gaps and penetration of light, to be experienced as annoying gleams of light.

[0015] Further disadvantages of using the conventional U-profile system, arranged exterior to an enveloping the screen, include disfiguring visual wear at the exterior visual surfaces of the curtain resulting from friction between curtain and U-profile during the many times the curtain are raised and lowered. Another problem is that two opposite U-profiles need to be secured to the frame prior to mounting the curtain as well as the distance between the legs of the U is a limiting factor for which kinds of curtain that can be fitted into the window frame. If a new curtain is too thick to be displaceable accommodated between the legs of the U-profile already in place, the U-profile must be replaced with a new that has a larger gap between the U's legs in order to be able to accommodate the edge of the curtain. Also, a double-walled pleated curtain is often thicker in the collapsed position than in the extended configuration. Thus, the distance between the first plane and the second plane increases when the length of the double-walled pleated curtain is decreased. The largest distance occupied between the first plane and the second plane defines the minimum acceptable distance between the legs of the U-profile, and often U-profiles in conventional use are chosen with a substantially safety margin.

[0016] New light-blocking curtains have various kinds of cellular structure and air pockets that not only effectively reduce light and noise but also provide increased insulation against heat and cold. The drawback is however that these improved light-blocking curtains are much thicker than old light-blocking curtains, so that a profile already in place often cannot be reused. Examples of new light-blocking curtains include the pleated cellular structures described in the above-mentioned patent documents.

[0017] The term "spacer means" comprises any structure extending between the opposite first and second faces of the length-adjustable screen, thus the spacer means is e.g. the structure that connects two opposing walls of a pleated double-walled curtain, or the zigzag-folding that provides the curtain with a thickness, partitions between slats, or any other similar means that creates a distance for the light to travel between two opposite faces or planes of a length-adjustable screen, such as a curtain.

[0018] It is a main aspect of the present invention to provide an improved system of the kind mentioned in the opening paragraph for blocking light coming from one room or space to another.

[0019] It is a second aspect of the present invention to provide an improved system of the kind mentioned in the opening paragraph that is easy to mount and can be adapted to fit into most framed light-incoming openings.

[0020] It is a third aspect of the present invention to provide an improved system of the kind mentioned in the opening paragraph wherein one profile can be used with many different thicknesses of light-blocking structures.

[0021] It is a fourth aspect of the present invention to provide an improved system of the kind mentioned in the opening paragraph which can be mounted in front of a sloped window, including skylights.

[0022] The novel and unique whereby this is achieved according to the present invention is the fact that the means for blocking light passing through said gap comprises

• at least one slot extending inside the spacer means of the length-adjustable screen between the first plane and the second plane from at least one free lateral edge of the length-adjustable screen, and
• a longitudinal key means protruding from the frame inside the opening opposite the at least one slot and configured to engage into said at least one slot.

[0023] Within the scope of the present invention a "key means" is a device configured with a first part that fits into the slot made in the lateral edge(s) of the length-adjustable screen and a second part that serves for mounting the key means onto the frame at the opening.

[0024] Because the key means is inserted inside the slots, preferably in slots made in both opposite free lateral edges of the length-adjustable screen, instead of being exterior to the length-adjustable screen, the protruding first part of the key means are entirely hidden inside the length-adjustable screen in the more or less extended configuration of the length-adjustable screen. No disfiguring visual wear at the exterior visual surfaces of the length-adjustable screen is generated. Moreover, one key means fits curtains of many thicknesses. The only proviso is that a lateral edge(s) has a slot extending into the spacer means.

[0025] In the preferred embodiment the slot may extend into the spacer means substantially perpendicular to the frame in the same plane as the engaging part of the key means.

[0026] A practical light-blocking system has a length-adjustable screen that can be lowered and raised smoothly. In conventional light-blocking systems a clearance or gap between the lateral edges of the length-adjustable screen and the U-profile or L-profile, and thus the frame, contributes to serve this purpose, but this clearance or gap leaves light to pass between frame and length-adjustable screen. Such clearance and gap is e.g. between 2.5 mm and 5 mm. The light to be blocked can be either natural light or artificial light.

[0027] By instead locating the clearance or gap between the length-adjustable screen and the key means inside the length-adjustable screen, as in the present invention, it is possible to use wider length-adjustable screens than in similar, conventional light-blocking systems mounted in e.g. U-profiles. Preferably the length-adjustable screen is as wide as the opening, and any crevices that allow light to pass between frame and length-adjustable screen are substantially eliminated.

[0028] In the conventional light-blocking systems, entrance of incident light may also happen due to an unavoidable light path created at the overlap and gap between U-profile or L-profile and the length-adjustable screen, or be due to light reflected by the exterior surface of the U-profile or L-profile.

[0029] Thus in conventional light-blocking systems the entry and exit of light to the light path are situated far more remote to the frame than in the inventive system, in which the free lateral edges of the length-adjustable screen are intimately aligned in close proximity to the frame and the slot-engaging key means so that a very superior light barrier is achieved.

[0030] In order to obtain the best possible control of lowering and raising the length-adjustable screen, as well as the best possible light-blocking capacity, the frame may be provided with opposite first and second longitudinal key means that protrude from the frame and first and second slots in respective free lateral edges of the length-adjustable screen, said slots being configured to engage said respective first and second longitudinal key means. In this configuration light-blocking can take place equally good on both free sides of the length-adjustable screen, and the length of the length-adjustable screen can be smoothly adjusted, using the key means as a guide rib.

[0031] In a simple embodiment the length-adjustable screen is just a pleated curtain made of a single sheet of material, where the spacer means are created during folding the sheet in zigzag. In this embodiment the spacer means are the folded material between opposing apices of the pleating folds.

[0032] In another simple embodiment the length-adjustable screen can be like an accordion.

[0033] In an alternative embodiment particularly suited for black-out curtains, noise-reducing installations, and thermal energy control installations, the length-adjustable screen can be a double-walled curtain of pleated material and the spacer means configured as an open cellular structure. Suitable examples of double-walled pleated curtains include but are not limited to the examples discussed above in relation to the prior art patent documents.

[0034] Many different kinds of spacer means consisting of open cells or interconnected layers of structures with open cells are contemplated within the scope of the present invention. In a preferred embodiment the shape of a cross-section of an open cell, taken in a plane parallel to the lateral edge of the length-adjustable screen, may be polygonal, preferably hexagonal, to create a honeycomb-like length-adjustable screen structure.

[0035] The pleated cellular structures can e.g. be made by stacked and mutually connected tubes of honeycomb-shaped cross- sectional area, however any cross-sectional area, including but not limited to squared, or even asymmetrical polygons are intended within the scope of the present invention. Also one or more lateral layers of stacks of tubular structures can be combined. A honeycomb light-blocking curtains is a very energy efficient version of a pleated light-blocking structure, having hexagonal tubular cells placed side-to-side.

[0036] The hexagonal honeycomb cross-section creates a lattice of cells using the least possible amount of material to obtain large volume between the first and second face of the length-adjustable screen. The first face and the second face can also be substantially flat flexible sheets interconneted and partitioned by means of transverse bands or strips. In such a simple system the length-adjustable screen can be composed of stacked tubular cells having squared end openings and squared cross-sectional areas. The contacting sides of the squared tubes may serve for securing the tubes to each other to create partitions between the open cells to form a length-adjustable screen. The joined tube sides creating the partitions becomes the spacer means.

[0037] An advantage of curtains, blinds or screens made of a plurality of stacked tubes or cells having honeycomb-shaped cross-sectional area is that two interconnected hexagon sides makes a flexible joint, and the parallel hexagon sides between opposite flexible joints can serve for securing the tubular hexagonal cells on top of each other to create the partitions between the open cells. In this design a length-adjustable double-walled pleated screen is created, and the joined opposite sides of the hexagon constitutes the spacer means.

[0038] Slots or recesses can be made simply by incising the lateral edges of the pleated curtain. For example, slots can be made by punching or laser-cutting through the collapsed length-adjustable screen along the lateral edges a distance into the spacer means. More than one slot may be provided in a lateral edge to co-operate with more protruding means of the key means.

[0039] The preferred design of slot and engaging key means are simply a suitable key means including a flat web to be inserted into a corresponding, substantially complementary shaped rectangular slot, or in any other slot of suitable shape. The slot may have a depth of between 1.5 cm and 3 cm and a width between 0.3 cm and 1.0 cm.

[0040] The flat web may expediently be at least a part of a T-shaped, L-shaped or U-shaped key means, but many modifications of shapes are contemplated by the present invention. The slot may be given any design and shape entirely complementary to, partly complementary to, or not complementary to the design and shape of the first part of the key means. For example the first part of the key means could be dovetailed, Y-shaped, or have a rounded free tip, and the bottom of the slot be complementary shaped, to further ensure that incident light does not pass through. However, first key parts having this configuration may all fit sufficiently well into a suitably dimensioned rectangular or tapered slot. The advantage of having an enlarged tip on the key means that key means and slot are not susceptible of disengaging.

[0041] The key means may be secured to the frame by means of an adhesive to facilitate easy assembly, replacement and removal. The need for drilling holes in the frame is eliminated and assembly time is considerably reduced. The key means can e.g. be extruded plastic profiles provided with an adhesive having an adhesion force selected to fix the profile to the frame. A releasable protective liner may protect the adhesive during storage and prior to adhering the key means to the frame.

[0042] The frame surrounding and bordering the opening can be selected from the group comprising a sash for a window, a frame around an artificial light source, a door case, a frame for a skylight, a centre-hung opening window sash, a top-hung window casement or a frame for a room divider, thus the frame usable in the system according to the present invention may be any frame surrounding an opening in e.g. a wall, irrespective of said opening is covered by a pane or similar means.

[0043] The preferred length-adjustable screen is a black-out curtain optionally provided with further light-blocking properties, such as dark colour, coatings, multiple different or similar layers, etc, including materials containing silver or a silver compound.

[0044] In one embodiment the length-adjustable screen is hoistable by means of curtain cords arranged between the first and second plane and retracted from the free edges, which leaves space for incising the slots

[0045] In another embodiment the length-adjustable screen is cordless and the slots can be of any suitable depth that does not compromise structural integrity and functionality of the length-adjustable screen.

[0046] In case the system according to the present invention is to be used at locations and spots that are beyond manual reach a motor may be provided for lowering and raising the length-adjustable screen.

[0047] The length-adjustable screen may have means for securing the length-adjustable screen to the frame, which means includes a top rail, and optionally means for weighing down the length-adjustable screen when lowered, optionally a bottom rail, wherein one, both or none of the top rail or the bottom rail have brushes for closing a gap between rail and frame.

[0048] The invention further relates to a method of mounting the above described system, which method comprises

• providing a length-adjustable screen having at least one slot extending inside the spacer means of the length-adjustable screen between the first plane and the second plane from at least one free lateral edge of the length-adjustable screen,
• providing a longitudinal key means configured to engage said at least one slot,
• mounting the key means on the frame with a part of the key means protruding from the frame into the opening, and
• mounting the slotted length-adjustable screen so that the key means engages with the oppositely facing at least one slot in the length-adjustable screen.

[0049] By means of the method according to the present invention effective blocking of light and/or heat passing through an opening encased by a frame can be achieved in a simple, effective and visually elegant manner. The length-adjustable screen can be raised and lowered in a controlled manner, because at least a part of the key means is inserted in a cooperative engaging slot, which engagement not only creates a barrier to light but also keeps the length-adjustable screen in a plane substantially flush with or parallel to the opening irrespective of unpredicted environmental influencing variables, such as positive or negative changes in air pressure close to the length-adjustable screen, or angle of the frame.

[0050] The invention will be described in further details below with reference to the drawing, wherein

[0051] fig. 1 shows, in an exploded perspective view, a fragment of a corner of an embodiment of a system according to the present invention,

[0052] fig. 2 shows the same, slightly enlarged, in an assembled state,

[0053] fig. 3 shows, by way of a section along line III-III in fig. 2, the system in fragmentary section, illustrating the engagement of slots of the length-adjustable screen and protruding parts of corresponding key means, and

[0054] fig. 4 is a plan view of the system seen in fig. 2 with the length-adjustable screen completely lowered so that the bottom rail rests on the bottom frame.

[0055] The figures of the drawing illustrate schematically the light-blocking principle and system according to the present invention by way of an exemplary embodiment, which shall not be construed as limiting for the many above-described modifications, variations and applications.

[0056] Accordingly, the invention will be exemplified below in relation to a vertical, pleated, cordless black-out curtain in front of a vertical window pane, but could quite as well have been described in relation to e.g. another framed opening without a pane, have curtain cords, be horizontal or be suspended in front of the opening of a centre-hung window sash at an angle of e.g. 45°.

[0057] The components of the system 1 seen in the exploded, fragmentary view of fig. 1 comprises a frame 2 that borders a window opening 3. A pane 4 (not seen in fig. 1) is mounted in the window frame 2 to cover the opening 3. How the pane 4 is mounted to the window frame 2 is not part of the invention and therefore only shown schematically.

[0058] The system further comprises a length-adjustable pleated screen 5 and a key means 6 in form of a longitudinal T-profile 6. The T-profile 6 consists of first part 7, in the case shown a longitudinal web 7, extending perpendicular from a second part 8, in the case shown the flat head 8 of the T.

[0059] The length-adjustable pleated screen 5 consists of a plurality of tubular structures 9 having hexagonal cross-section A_H. Tubular structures 9 are joined, each on top of another, to create the length-adjustable pleated screen 5. The length-adjustable pleated screen 5 has a span to completely cover the opening 3 and the windowpane 4 when the length-adjustable pleated screen 5 is in its lowermost position. That is to say, the length-adjustable pleated screen 5 must include so many tubular cellular structures 9 that the length-adjustable pleated screen can span the distance between a top part (not shown) of the frame 2 and a bottom part 10 of the frame 2 when the length-adjustable screen 5 is extended. When the length-adjustable pleated screen 5 is lowered its apices 11a,11b, on respective opposite first face 12a and second face 12b, define respective opposite first plane 13a and second plane 13b. The width of the length-adjustable screen 5 is selected to be substantially the same as the width of the frame opening 3, although a small difference is acceptable to take account of or compensate for parameters such as oblique frame angles and the size and dimension of the second part 8 of the key means 6. The difference between the width of the length-adjustable pleated screen 5 and the frame opening 3, i.e. the lateral clearance C between frame 2 and length-adjustable pleated screen 5, must however not be so small that the black-out curtain cannot be operated smoothly.

[0060] When the hexagonal tubular structures 9 are combined into the length-adjustable pleated screen 5, adjacent joined hexagon faces 14 of the tubular cellular structures 9 define an inherent, integral spacer means 15, that distances the first plane 13a from the second plane 13b and provides the thickness of the length-adjustable pleated screen 5.

[0061] Since for illustrative purposes only a fragment of the system 1 is seen in figs. 1 and 2, only the first lateral edge 16 of the length-adjustable pleated screen 5 is visible. It shall however be understood that an opposite second lateral edge 16 is similarly constructed. Both lateral edges 16 have a slot 17. As seen better in fig. 3, the slots 17 are oriented confronting and engaging the web 7 of the respective key means 6. A slot 17 is e.g. 2 cm deep and made by using a suitable punch die (not shown) to punch through the spacer means and wall of tubular structure 9 along the lateral edges 16 of the length-adjustable pleated screen 5 when in a collapsed state.

[0062] The length-adjustable screen 5 also has a bottom rail 18 for weighing down the length-adjustable screen 5 when it is lowered, and a top rail (not shown) for mounting the length-adjustable screen to a top frame part (not shown).

[0063] Fig. 2 shows the system 1 in the assembled state where the key means 6 is attached in vertical position to a vertical frame part 19 of the frame 2, e.g. simply by means of an adhesive (not shown). Any other attachment means can be used, including screws or nails.

[0064] The web 7 of the key means 6 projects into the confronting slot 17 in the spacer means 14 at the lateral edge 16 of the double-walled length-adjustable pleated screen 5. The opposite lateral edge 16 (as seen in fig. 3) is arranged in a similar manner which allows the length-adjustable pleated screen to be guided up and down by the web 7 in a substantially vertical plane in front of the pane 4, to cover said pane if black-out of light is needed.

[0065] The web 7 of the key means 6 are not visible in the extended configuration of the length-adjustable pleated screen 5. The web 7 is accommodated inside the slot 17 and hidden between first and second screen faces 12a,12b. Thus the web 7 is not exposed to incident light and no unpleasant light reflections are emitted from the key means 6. The gap C between the lateral edges 16 of the screen 5 and the frame 2 is inferior.

[0066] As seen in the plan view of fig. 4 the length-adjustable screen 5 fits neatly over the area of the window opening 3. The lateral edges 16 of the length-adjustable screen 5 is very close to the frame 2, because the length-adjustable screen 5 overlaps the web 7. Light is completely prevented from passing from the first plane 13a to the second plane 13b.

[0067] To be able to illustrate the small details relevant for the function and a large system only a fragment of the system 1 with a corner of the frame 2 is seen in figs. 1 and 2. Fig. 3 indicates the symmetry of the system 1 at the opposite lateral edges 16. As seen in particular in fig. 3 and fig. 4 the gaps C between the lateral edges 16 of the length-adjustable screen 5 and the frame 2 is extremely small and blocked by the longitudinal engaging web 7, so that light is significantly prevented from passing

[0068] A pleated screen or curtain for a top-hung casement window needs to be distended in an oblique angle. The method used today is enforcing and keeping the lateral edges of the screen or curtain apart using steel wires or ropes. The wires are mounted in the corners of a top list or the corners of the head rail and the pleating is secured to said top list or head rail. Brackets at the bottom frame corners serves to secure the wires to keep the screen distended and flush with the window opening. Although this technique is good, it is complex and requires that the wires, ropes or cords is stretched and kept tensioned. Ropes or cords under tension have a tendency to slack over time and need frequent expensive re-tension.

[0069] If instead the system 1 according to the present invention is implemented in the top-hung casement window the web 7 of the key means 6 keeps the pleated screen in the angled position, e.g. between 0° and 90°, and often 45°. Thus the key means is a simple means to prevent the screen from dropping to a vertical position and for keeping the screen flush with the opening, i.e. the pane.

[0070] The maximum angle in relation to the screen's width depends on the type of screen material. If the pleated screen material is of the kind where the distance between the first plane and the second plane is about 25 mm, a screen having a width of e.g. 120 cm can be mounted and operated at an angle of about 30°.

[0071] The screen 5 of the inventive system 1 is easy to mount on any kind of frame 2. The screen 5 can be mounted fully recessed in the frame or just partly recessed in the frame. The screen can even be mounted exterior to the opening, e.g. by using an L-profile where the long leg serves as the first part 7 of the key means 6 similar to the web 7 and the short leg serves the same function as the second part 8 of the key means 6, similarly to the head 8.

[0072] The new system is easy to mount, does not require re-levelling or re-adjustment, and can be used for blacking out light passing through a plurality of openings, including but not limited to window openings.

Claims

1. A system (1) for blocking light and/or thermal energy passing through an opening (3), the light-blocking system (1) comprises

- a length-adjustable screen (5) of the kind that has a first face (12a) defining a first plane (13a) opposite a second face (12b) defining an opposite second plane (13b),

- which first face (12a) and second face (12b) are interconnected at a distance from each other by means of a spacer means (14),

- a frame (2) bordering at least a part of the opening (3), and

- means for blocking light passing through a gap between at least one lateral edge (16) of the length-adjustable screen (5) and the frame (2),

characterised in that the means for blocking light passing through said gap comprises

- at least one slot (17) extending inside the spacer means of the length-adjustable screen (5) between the first plane (13a) and the second plane (13b) from at least one free lateral edge (16) of the length-adjustable screen (5), and

- a longitudinal key means (6) protruding from the frame (2) inside the opening (3) opposite the at least one slot (17) and configured to engage said at least one slot (17).

2. A system (1) according to claim 1, characterised in that

- the frame (2) has opposite first and second longitudinal key means (6) that protrude towards each other from the frame (2), and

- the length-adjustable screen (2) has first and second slots (17) in respective free lateral edges (16) of the length-adjustable screen (2) configured to engage said respective first and second slots (17).

3. A system (1) according to claims 1 or 2, characterised in that the length-adjustable screen (2) is a pleated curtain.

4. A system (2) according to claim 1, 2 or 3, characterised in that the length-adjustable screen (5) is a double-walled curtain of pleated material and the spacer means (14) is configured with an open cellular structure (9).

5. A system (1) according to claim 4, characterised in that the shape of a cross-section of the open cells taken in a plane parallel to the lateral edge (16) of the double-walled length-adjustable screen (5) is polygonal, preferably hexagonal.

6. A system (1) according to any of the preceding claims 1 - 5, characterised in that the key means (6) includes at least a part being T shaped, L-shaped or U-shaped.

7. A system (1) according to any of the preceding claims 1 - 6, characterised in that the key means (6) is secured to the frame (2) by means of adhesive.

8. A system (2) according to any of the preceding claims 1 - 7, characterised in that the frame (2) bordering the opening (3) is selected from the group comprising a sash for a window, a frame around an artificial light source, a door case, a frame for a skylight, a centre-hung opening window sash, a top-hung window casement or a frame for a room divider.

9. A system (1) according to any of the preceding claims 1 - 8, characterised in that the length-adjustable screen (5) is a black-out curtain.

10. A system (1) according to any of the preceding claims 1 - 9, characterised in that the length-adjustable screen (5) is hoistable by means of curtain cords arranged between the first (13a) and second plane (13b) and retracted from the free lateral edges (16).

11. A system (1) according to any of the preceding claims 1 - 10, characterised in that the length-adjustable screen (5) is cordless.

12. A system (1) according to any of the preceding claims 1 - 11, characterised in that the system (1) comprises a motor for lowering and raising the length-adjustable screen (5).

13. A system (1) according to any of the preceding claims 1 - 12, characterised in that the length-adjustable screen (5) has means for securing the length-adjustable screen to the frame, which means includes a top rail, and optionally means for weighing down the length-adjustable screen when lowered, optionally a bottom rail, wherein one, both or none of the top rail or the bottom rail have brushes for closing a gap between the rail and the frame.

14. A system (1) according to any of the preceding claims 1 - 13, characterised in that the at least one slot (17) has a depth of between 1.5 cm and 3 cm and a width of between 0.3 cm and 1.0 cm.

15. A method of mounting a system (1) according to any of preceding claims 1 - 14, comprising

- providing a length-adjustable screen (5) having at least one slot (17) extending inside the spacer means of the length-adjustable screen between the first plane (13a) and the second plane (13b) from at least one free lateral edge (16) of the length-adjustable screen (5),

- providing a longitudinal key means (6) configured to engage said at least one slot (17),

- mounting the key means (6) on the frame (2) with a part (7) of the key means (6) protruding from the frame (17) into the opening (3), and

- mounting the slotted length-adjustable screen (5) so that the key means (6) engages an oppositely facing slot (17) in the spacer means (14) of the length-adjustable screen (5).

Drawing