It has been known to produce reflective slats consisting of two concave partial pieces wherein the first one facing the outer space serves for light deflection to the outside and the second one facing the interior space serves for light deflection into the interior space. The disadvantage of these slats of DE 102 60 71 1 A1 consists in the low rigidity in case of wind pressure. The slats might crack since, for optical reasons, the central edge may be shaped only as slightly angled. A further disadvantage consists in that the slats, when in the shut-off state, do not close completely. Flat sun, in particular, might still be deflected, via the second partial piece, by deflection onto the under side of the upper slat and hence into the interior space. Hence the Venetian blind serves only for shadowing the room not, however, for darkening the room. It has also been known to produce z-shaped slats which display a plurality of inflexions wherein individual surface areas of their upper side are convex-shaped. These slats which are common nowadays are characterized by a high stiffness.

The disadvantage of these prior art slats consists in the glare on the slat upper sides if they are provided with a shining lacquer or an aluminum-shining reflective surface. In case of open Venetian blinds, the convex upper sides scatter the light into the user's eye in the interior room. These glaring effects render it impossible to employ the prior art z-shaped slats for precise light guidance to achieve an optical heat regulation of the solar incidence, and with reflective surfaces. From DE 43 10 718 A1 , Figure 5, a three-dimensional light guidance profile has been known the upper side of which has a stepped contour, wherein a few segments of the first retro-reflective concave portion (508) and the segments, together with a second concave portion (509) oriented towards the interior space, form an acute angle relative to each other, wherein the segments of the second portion are disposed steeper than the segments of the first portion. The disadvantage is that with a view to the steeper angle of incidence of the second portion, illumination of the room depth is not possible. If the complete profile is turned more flat in order to effect a more flat light deflection towards the room depth, the sun will also be guided, via the first portion into the interior space while a quantitative control of the relation of solar irradiation to solar reflection and an optical heat control and energy management with a slat curtain is not possible. The desired flat light influx as well as the light deflection will be accomplished only via a second deflection on the under side of the light guidance profile. By the principle of the two-fold deflection or by the fluctuation of the light between the upper sides and the under sides of neighboring profiles, increased non-desired heat development will come up since at each reflection, portion of the radiation is absorbed. Under sides and upper sides form a light guidance system having the disadvantage that in view of the three- dimensional profile shape it is not possible to lift the light guidance system, Venetian blinds like, and to join it together to obtain a slat package.

It is therefore the task of the present invention to provide a stackable z-shaped slat having a high moment of resistance against mechanical attack and against high wind pressure and to shape at the same time the slats so that they will serve

as light guidance slats for improved interior space illumination with day light to save electric lighting and, at the same time,

as sun protection slats against direct sun incidence and, at the same time, as light deflection slats for passive cooling and, at the same time, for an improved transparency and, in the closed state,

as a darkening measure. These development aims will be realized by the characterizing features and the engineering instructions as in accordance with the main claim.

The advantage of the present invention under static points of view is the stiffness of the slat of thin aluminum material by the two-fold inflexion of the central partial face at the angle β-ι, or β ₂ , and the concave shape of the surfaces which promote the edge rigidity of the slats. Under daylight-technological points of view, the structure has so been chosen that opposing optical functions will result in the portion situated towards the outer space and the portion situated towards the interior space. The portion situated towards the outer space deflects the high summer sun mono-reflectively; the portion situated towards the interior space mono-reflectively deflects the daylight to the ceiling (Figures 10 - 13). A further aim is to promote, by particularly shaping the z-shaped slats, a good optical lock to darken the room when the curtain is closed. The term mono-reflective means that the slats having an optimum angle of incidence for fulfilling the guiding-in or guiding-out function, deflect the light by one single reflection into the desired direction without using the under side of the upper slat. This does not, however, exclude that in case of respective sun hours and slat angles of incidence, light deflection to the under side of the upper slat will result. It is rather decisive that, at eye level of a user, neither glares on the slat under side nor avoidable heat developments in case of high summer sun will occur. This is obtained in that the slat upper sides react independently without forming an optical multi-reflective system with the neighboring slat. Further advantages will become obvious from the drawings wherein

Fig. 1 shows the slats according to the invention together with their optical functions,

Fig. 1.1 shows a particularly advantageous embodiment of a slat according to the invention

Fig. 2 shows the slat of the invention in a locked position Figs. 3, 4, 5 and 6

show variants of the slats of the invention in their basic shapes

Figs. 7, 8, 9 show further variants of the slats of the invention in modifications of the basic shapes

Figs. 10 to 12 show the ray track of the deflected rays for various angles of incidence of the sun and slat tipping angle

Figs. 13 and 14 show aluminum-extruded large slats with integrated artificial illumination. Figure 1 shows slat 10 to 13 consisting of partial faces 14 to 17 oriented to the outer space and the partial faces 18 to 21 oriented to the interior space, and the centrally disposed partial faces 22 to 25. In order to obtain the advantages substantial of the present invention, the following engineering instructions are valid: CH > α ₂ , βι < β ₂ . The first partial face disposed towards the outer space is always steeper than the portion oriented towards the interior space. ch is the angle formed between a connecting line V between two end points 30, 31 of a slat and a chord \ of the first concave partial face 15. The chord results as the connecting line between the end point 31 of the slat and the break 32 towards the center portion.

The angle a ₂ is obtained by a chord V ₂ through the end point 30 and a further end point 33 of the partial face 19 at the break towards the center portion 23. βι and β ₂ are the angles between the central partial face 23 or of an assumed short connecting plane and a tangent t-ι or t ₂ at the end points 32 and 33 of the partial faces disposed to the interior space or to the outside space, respectively.

Following this engineering instruction, a slat having two opposing optical properties is obtained. Sun radiation 40 impinging at an angle γ on the partial face 16 oriented to the outer space and sun radiation 41 also impinging at an angle γ on the partial face 20 oriented to the interior space, each, is deflected into a different direction. The sun impinging on partial face 16 is deflected, in the meaning of passive cooling, to the outside, the sun 41 impinging on partial face 20 to the inside for improving interior space illumination.

It is not essential of the invention to shape the partial faces on its upper sides circular and concave. The definitions on the connecting lines V serve only as a help for constructing with arched areas. The partial faces may also be made plane. In their central portion 22 to 25, the slats include a perforation to draw a drawstring 26 in so that a swing-off of the slat towards the outside is possible. By tilting the slats, diverse light deflection effects may be obtained, also with reference to the varied sun incidence angles γ. A further advantage of the slats is the screening out of sun irradiation 40 which is mono-reflectively deflected from the partial face 16 oriented to the outside back into the outer space. Rays 42/45 may also be guided to the under side 43, or 44, of the upper slat. In this way, blinding of the viewer from the interior space is advantageously avoided since the illuminated face portions 43/44 cannot, or only slightly, be perceived from the interior space.

Figure 1.1 shows once more the optical relations of the individual partial faces relative to each other. At the point of intersection S, between drawstring 47 and the third partial face 49, a perforation 48 is provided through which the drawstring 47 is threaded. In their closed status, the slats form an optical lock, as can be taken from Figure 2. The perforation 48 is advantageously staggered about the measure x from the middle of the central portion in the direction to the partial face oriented to the interior space and/or are imported into it. In a horizontal position, between the central partial face 49 and the drawstring 47, there is an angle δ of between 5 and 50 degrees. According to the definition, the horizontal position is obtained when the connecting line V is approximately horizontally aligned. Figure 2 shows the slats 50 to 52 from Figure 1 in a locked position. The drawstring 53 against which the slats lean on is shown. The slats include flanged laps 54 to 59 into which the clips for the loop strings (not shown) and the welting are drawn in so that the slats rest tightly one upon the other and in this way especially serve for darkening. Figures 3, 4, 5 and 6 show variants of the slat of the invention, without the flanged lap though. The individual slats are characterized by the following features:

Figure 3 shows a small partial face 60 oriented to the outer space. In the case of this slat, light deflection towards the interior space via partial face 61 prevails. Figure 4 shows a broad partial face 62 oriented towards the outer space and a smaller partial face 63 oriented to the interior space. In this case, the sun deflection and the passive cooling prevail. Deviations of angles βι and β ₂ are extreme. The central partial face 67 is broad and collects light radiation from the lower slat. Figure 5 shows an almost symmetrical surface distribution of the partial faces 64 and 65.

Figure 6 is characterized by a very small central partial face 68. Figures 7, 8 and 9 show further variants of the present invention.

The slats may show further inflexions and partial faces as shown in Figures 7, 8 and 9. Particularly by arching the central partial faces, as shown in Figures 8 or 9, favorable static effects may be obtained. They follow, nevertheless, the archaic basic types of Figures 1 to 6. The archaic basic shapes are shown, dotted, in Figures 7, 8 and 9 respectively. Particularly the data as to the angles βι and β ₂ refer to the archaic basic shapes of variants 7 to 9, independently on whether individual surface portions are angle-shaped, rounded-off or, for light-technological or static reasons, undulated or concave on the upper side. Bending at the outer edges towards the side of the room or the outside, too, as in Figure 7, should be considered as details of the present invention, in order to obtain a better optical lock.

The present invention encompasses all variants of slat contours which follow the engineering instructions of the characterizing clause of the main claim independently on whether for instance the connecting piece between the partial faces oriented toward the outside or toward the inside are made straight or arched. The engineering instruction refers for instance to the shortest connection between end points of the above partial faces.

The end points of the light in-guiding or light out-guiding areas should be considered as the outer end points of the slat contours on the irradiation or the radiation side, independently on elongations or bending of appendices.

A particularly advantageous variant of the slat of Figure 10 - 12 is characterized by the following angles:

Qi ~ 20° for a ₂ = 0°, βι ~ 1 15°, β ₂ ~ 135°, ε ~ 35°

A slat having such an angular characteristic has, in the vertical, a distance relative to the slat disposed above or below of from d/b ~ 0.7 up 1 0.9, preferably 0.81 .

Within one curtain, the slats may be disposed at different angles of incidence the slats in the upper curtain portion being engaged more flat and in the lower part stronger. A typical angle of incidence of the slats below eye level of a standing person amounts to 16° relative to the horizontal. In the upper curtain portion, the slat, or the portion facing the interior space, may have an angle of incidence of 0° or of < 0°. From above downwards, the slats may also be disposed continuously steeper in that, by means of different loop strings, the distance between the outer edges of neighboring slats is selected smaller and between the interior edge of neighboring slats is selected larger.

The slats are arranged either at the outside, at the inside or between the panes and show typical widths b of from 15 mm up to 300 mm and significantly more. The slats are produced either from steel or aluminum sheets by roll shaping or by an aluminum extrusion process, and are hung up rigidly, pivotally, or as Venetian blinds.

The preferred area of application includes Venetian blind slats which when hoisted up rest into one another thus forming small slat packages. To this end, one selects β-ι > 90°. The difference between β ₂ - βι should be > 20°. In Figures 10 to 1 1 , the ray track for advantageous slat shaping and a slat position between 1 m and 1 .6 m headroom are shown. One can clearly recognize that in spite of different sun incidence angles, the slat upper sides deflect the sun primarily mono- reflectively to the inside and to the outside. The portions oriented towards the interior space are undulated, that is they are concavely/convexly shaped.

In the upper window area, the slat may be disposed more flat in order to deflect the winter sun deeper into the interior space. This is illustrated in Figure 12. In the case of these slat positions, and in case of very flat sun, in addition, a deflection into the depth of the room at the first portion will occur. At higher angles of incidence, the sun impinges onto the reflective face oriented towards the interior space and deflects the light flat into the room while the portion facing the outer space deflects the light to the under side of the upper slat. In order to avoid glare at the under side, it is preferably coated in white, grey or colored. In order to avoid reflections from the railing area in the eye of the user, the slats in the railing are disposed very steep. Figure 14 shows large extruded aluminum slats having the characteristic structural features of the slat upper sides according to Figures 10 to 12 and other. The slats, however, show a belly 70 thus forming hollow sections. Into such hollow section in the area of the central partial face, a glass-covered illuminant 71 is built in which, as can be taken from Figure 15, will project light 72 to 75 into the depth of the room and to the ceiling.

In this way, an integrated artificial light and daylight solution has been created. Poorer daylight will be supported by the electric illumination from the direction of the deflected light from the sky. An integral light flux of artificial light and daylight will result. From light ray 56 it can be taken that the daylight reflection of the partial faces oriented towards the interior space will serve to deflect the artificial illumination as well. Such slats including illuminants 80 to 82 are preferably installed at a height of 1.5 m to 2.0 m and they are, therefore also suited to illuminate the interior room to its complete depth.

It is either a linear luminaire including reflector and glass cover 51 or light emitting diodes or other light-emitting illuminants which may be installed in the slat section. A comparable artificial light and daylight solution is also possible for simple slat structures in that partial face 49 of Figure 1 .1 is provided with LEDs or OLEDs.

Further embodiments consist in that the partial face disposed towards the outer space is provided with photovoltaic cells for current generation. In this case, the partial faces are preferably made planar and are equipped with organic or crystalline energy converters.

The underside of the slats may be micro prism structured in that prism-shaped longitudinal grooves extend in parallel to the longitudinal edges. By these longitudinal grooves which are preferably asymmetrically shaped, light radiation reflected from the partial face oriented toward the outer space to the under side of the upper slat, may be deflected to the outside. In any case, it can be avoided that, viewed from a user of the interior space, glare will come up at the slat under side. The slat under sides may also be shaped as micro prisms. This is particularly obvious when using extruded slats. As an alternative, the slat belly 91 of slats 90, as shown in dotted lines, has for instance a micro prismatic structure.