FIELD OF THE INVENTION:

The invention relates to a translucent device comprising translucent light-spreading structures for angularly depending haze.

The invention further relates to a translucent panel comprising the translucent device and to a greenhouse comprising the translucent device.

BACKGROUND OF THE INVENTION:

Translucent devices for limiting the impinging direct sunlight are known. They are used, inter alia, as roof panels in greenhouse for diffusing the light inside the greenhouse. According to Hemming, Mohammadkhani and Dueck (Diffuse greenhouse covering materials material technology, measurements and evaluation of optical properties, Acta Horticulturae 797 (2008) p. 469 - 476), at high irradiation levels diffuse greenhouse coverings result in better light distribution, lower crop temperature, decreased transpiration, and increased photosynthesis and growth, despite the fact that these coverings generally have lower light transmission compared to clear transparent greenhouse coverings. At low irradiation levels however, the optimal conditions for the plant are obtained using clear transparent greenhouse coverings to maximize the Photosynthetically Active Radiation level.

This means that an optimal greenhouse covering should be diffusive for high irradiation levels (summer conditions, midday conditions) and clear for low irradiation levels (winter conditions, morning and evening conditions).

The main performance parameters for greenhouse coverings are transmittance and haze. Haze is defined as the fraction of the light transmitted by a substrate, that is scattered or refracted in directions deviating from the direction of the incident light. More haze means less transmittance substantially parallel to the incident light and thus more light being spread, and vice-versa. The optimal greenhouse covering should therefore have properties that result in a relatively high haze value for relatively high irradiation levels and a relatively low Haze value for relatively low irradiation levels.

US patent 7,033,736 discloses structured screens for controlled spreading of light. US patent 6,456,437 discloses a structured surface for controlling the spreading of light. US patent 4,997,686 discloses a patterned product having a three-dimensional appearance comprising a transparent substrate with a discontinuous pattern coating in combination with a second pattern coating on a separate surface.

A drawback of the known system is that none of these systems provides a device in which the haze may be passively controlled.

SUMMARY OF THE INVENTION:

It is an object of the invention to provide a system for passively controlling the haze of transmitted light.

According to a first aspect of the invention the object is achieved with a translucent device for passively varying a haze of the transmitted light, the translucent device comprising a first surface and a second surface arranged opposite the first surface, each one of the first surface and second surface comprising translucent light spreading elements (40) arranged in recurrent patterns, the recurrent patterns are configured for providing a maximum haze of the transmitted light for light impinging at a first angle of incidence, and for providing a minimum haze of the transmitted light for light impinging on a second angle of incidence, different from the first angle of incidence.

Translucent in this document means somehow transmitting light. This includes transparent and diffusely transmitting light and any other transmission of light. The present invention is based on the insight that the situation where high irradiation levels occur in greenhouses is related to a different range of incident angles than the situation under which low irradiation levels occur. It is also based on the insight that the angular dependency of haze can be controlled by a combination of opposite patterns of light diverging surface structures. The present invention provides a passive control of haze properties by a transparent sheet, with two opposite surfaces each partially occupied by light diverging surface structures in recurrent patterns. When the two recurrent patterns are shifted with respect to each other parallel to the first surface, the angle of incidence at which the maximum haze occurs may be adapted. This allows to maximize the haze for angles of incidence corresponding with high irradiation levels and to minimize the haze for angles of incidence corresponding with low irradiation levels. For example, when applying the translucent device on a greenhouse, the recurrent patterns on both the first and second surface may be configured such that when the sun is relatively low, the haze is at a minimum level and when the sun is relatively high, for example, at noon, the haze is at a maximum level, substantially diffusing all transmitted light into the greenhouse. The recurrent pattern on the individual surfaces may need to be adapted for the position of the greenhouse and for the angle of declination of the translucent device which typically functions as a roof panel of the greenhouse.

In an embodiment of the translucent device, the translucent light spreading elements are configured for refracting and/or diffusing light impinging on the translucent light spreading elements.

In an embodiment of the layout modification system, translucent light spreading elements of the first surface and/or the second surface are constituted of bands of light spreading surface structures, the bands comprising a width being smaller than a pitch between the bands. A benefit of this embodiment is that the amount of haze may be relatively easily controlled via adapting the width of the bands.

In an embodiment of the layout modification system, each band of light spreading surface structures comprises a grating constituted of a parallel arrangement of individual light spreading surface structures, the grating having a further pitch smaller than the pitch between the bands.

In an embodiment of the layout modification system, the grating is arranged parallel or perpendicular to the bands. A benefit of this embodiment is that the direction in which the light is being spread by the surface structures can controlled by the direction and the line-space density of the grating.

In an embodiment of the layout modification system, the bands on each of the first surface and/or second surface are arranged substantially parallel to each other. A benefit of this embodiment is that the direction in which the haze has its angular variation can be controlled.

In an embodiment of the layout modification system, the pitch of the bands of translucent light spreading elements of the first surface and the second surface are substantially equal. A benefit of this embodiment is that the characteristics across the translucent device are substantially homogeneous across the first and second surface. Alternatively the pitch of the bands of the first surface may be different compared to the second surface which may cause local variations of the haze produced from the first and second surface which may be beneficial in specific applications.

In an embodiment of the layout modification system, the recurrent pattern of translucent light spreading elements of the first surface are shifted with respect to the recurrent pattern of translucent light spreading elements of the second surface in a direction parallel to the first surface. A benefit of this embodiment is that the shift determines at which angle of the impinging light a maximum haze is obtained. This may, for example, be used to determine an angle of inclination of the translucent device when the translucent device is used, for example, as a roof panel in a greenhouse. By shifting the recurrent pattern of the first surface with respect to the second surface, still sunlight impinging on the greenhouse at noon would have a maximum haze.

In an embodiment of the layout modification system, the recurrent pattern of translucent light spreading elements of the first surface are rotated with respect to the recurrent pattern of translucent light spreading elements of the second surface in a plane substantially parallel to the first surface.

In an embodiment of the layout modification system, the translucent light spreading elements comprise indentations into and/or protrusions out of the first surface and/or second surface. Protrusions may be done by etching the remainder of the surface away. Alternatively, the protrusions may be generated by, for example, applying a foil on the surface which foil comprises the protrusions. A benefit of this embodiment is that indentations may be easily produced using well-known etching techniques. In such techniques, the exact shape of the indentations may be determined by the etching process. Alternatively, protrusions may be generated by etching the remainder of the surface away. However, the protrusions may also be generated by, for example, applying a foil on the surface which foil comprises the protrusions.

In an embodiment of the layout modification system, the translucent device comprises a translucent sheet comprising both the first surface and the second surface. The translucent sheet may be transparent when no light spreading elements are arranged on the first surface and second surface.

In an embodiment of the layout modification system, the translucent device comprises a first translucent sheet comprising the first surface and comprises a second translucent sheet comprising the second surface. A benefit of this embodiment is that after production the first translucent sheet and the second translucent sheet the orientation of the two translucent sheets may still be altered to fine-tune the angles at which maximum and/or minimum haze occurs in the translucent device.

A further benefit of this embodiment is that the first surface comprising the recurrent pattern may be arranged to face the second surface comprising the recurrent pattern. In such an embodiment, the recurrent pattern is arranged in the space between the first and second translucent sheet. As this space between the first and second translucent sheet is generally a fully closed space, no dirt or contamination can enter the recurrent pattern which may reduce the efficiency of the spreading of the light by the pattern thus keeping the recurrent pattern clean. In such an embodiment, the outer surfaces of the translucent device is free from light spreading elements which eases the cleaning required of the translucent device.

The first and second translucent sheet may be transparent when no light spreading elements are arranged on the first surface and second surface.

In an embodiment of the layout modification system, the translucent device comprises shifting-means for shifting the first surface with respect to the second surface. A benefit of this embodiment is that also after applying the translucent device, the angle at which maximum and-or minimum haze occurs may still be altered to optimise for changing conditions (for instance Summer or Winter conditions).

In an embodiment of the layout modification system, the first translucent sheet and the second translucent sheet are configured for generating a translucent safety-glass panel. The safety-glass panel generally has two translucent plates connected together, preferably having a translucent or transparent foil arranged between the two translucent plates. This translucent or transparent foil may be a plastic translucent or transparent foil arranged for gluing the first translucent plate to the second translucent plate. Furthermore, this translucent foil generally has the ability to keep the translucent device together when one or both of the translucent sheets may break. Especially when using the translucent device as roof panel in a greenhouse, this roof panel should preferably be made of safety- glass such that when some of the roof panels break, people inside the greenhouse may not be injured.

According to a second aspect of the invention, the object is achieved with a greenhouse comprising the translucent device according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS:

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings:

Figure 1 is a schematic view of a typical geometry o f a greenhouse covering with east and west facing roof panels in relation to the solar path during the day, Figure 2 shows the components in the vertical east-west plane of the parallel rays of direct solar radiation corresponding to a point in time in the morning, mid-day and evening,

Figure 3A shows the cutting edge of a transparent sheet with two opposite surfaces each partially occupied by light diverging surface structures,

Figure 3B shows the cutting edge of a pair of transparent sheets in which each of the transparent sheets comprises the recurrent patterns,

Figure 3C shows the cutting edge of a pair of transparent sheets in which each of the transparent sheets comprises the recurrent patterns arranged in the space between the two transparent sheets,

Figure 3D shows the cutting edge of a pair of transparent sheets in which each of the transparent sheets comprises two opposite surfaces having the recurrent patterns,

Figure 4 is a top view of one of the surfaces of the transparent sheet of Figure 3,

Figure 5 shows a top view of one of the surfaces of a transparent sheet in which the structured bands are formed by concave parallel channels with length x ₂ oriented in a direction perpendicular to the direction of the bands,

Figure 6 shows a cutting-edge view of a transparent sheet with two opposite surfaces each partially occupied by light diverging surface structures in recurrent patterns (schematically shown as thick bands), Figure 7 shows a cutting-edge view of a transparent sheet with patterns according to Figure 6, for which x1 = x2 = x3 = x4,

Figure 8 shows the same transparent sheet with patterns of Figure 7, at the angle of incidence for which part of the incident solar rays is transmitted without interaction with either the structured bands, Figure 9 shows a graph of the relative Haze as function of the angle of incidence for the example of the transparent sheet of Figures 7 and 8.

The figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. Similar components in the figures are denoted by the same reference numerals as much as possible.

DETAILED DESCRIPTION OF THE EMBODIMENTS:

Figure 1 is a schematic view of a typical geometry o f a greenhouse 50 covering with east and west facing roof panels 1 and 2 relation to the solar path 3 during the day, showing different positions of the sun in morning 4, mid-day 5 and evening 6 in the vertical east-west plane. Figure 2 shows the components in the vertical east-west plane of the parallel rays of direct solar radiation corresponding to a point in time in the morning 7, mid-day 8 and evening 9, relative to the greenhouse roof panels 1 , 2.

Figure 3A shows the cutting edge of a transparent sheet 30 with two opposite surfaces 21 , 22 each partially occupied by light diverging surface structures 1 1 and 12 in the form of concave parallel channels 40 in recurrent patterns in which the two opposite patterns are mutually shifted y (see Fig. 6).

Figure 3B shows the cutting edge of a pair of transparent sheets 31 , 32 in which each of the transparent sheets 31 , 32 comprises the recurrent patterns 40 which may be shifted relative to each other. A benefit of this embodiment is that the distance between the recurrent patterns 1 1 , 12 is relatively large in a direction perpendicular to the first surface 21 thus enabling a relatively large range in which substantially all light is transmitted into, for example, the greenhouse 50. As such, this arrangement may be beneficial when not too much sunlight is available. Figure 3C shows the cutting edge of a pair of transparent sheets 31 , 32 in which each of the transparent sheets 31 , 32 comprises the recurrent patterns 11 , 12 arranged in the space between the two transparent sheets 31 , 32. A benefit of this embodiment is that the recurrent pattern 11 , 12 is arranged in a substantially closed environment in the space between the two transparent sheets 31 , 32 and as such less or no dirt may reach the recurrent pattern 1 1 , 12 thus the efficiency of the recurrent pattern 1 1 , 12 is not reduced by the filling of the recurrent pattern 1 1 , 12 by dirt.

Figure 3D shows the cutting edge of a pair of transparent sheets 31 , 32 in which each of the transparent sheets 31 , 32 comprises two opposite surfaces 21 , 22 having the recurrent patterns 1 1 , 12. This allows a more accurate control of the haze created by the two translucent sheets 31 , 32. The shape and density of the bands 1 1 , 12 may differ per transparent sheet 31 , 32 generating a specific angular relationship between the impinging light and the haze created in the transmitted light, transmitted through the translucent device 100. A benefit of this embodiment is that the distance between the recurrent patterns 1 1 , 12 is relatively large in a direction parallel to the first surface 21 thus enabling a relatively large range in which substantially all light is transmitted into, for example, the greenhouse 50. As such, this arrangement may be beneficial when not too much sunlight is available.

Figure 4 is a top view of one of the surfaces 21 , 22 of the transparent sheet 30 of Figure 3A, showing the pattern 40 as bands with broadness X2 of concave parallel gratings 42, with distance Xi between the bands comprising the grating 42

Figure 5 shows a top view of one of the surfaces 21 , 22 of a transparent sheet 30 in which the structured bands are formed by concave parallel grating 44 with length x ₂ oriented in a direction perpendicular to the direction of the bands.

Figure 6 shows a cutting-edge view of a transparent sheet 30 with two opposite surfaces each partially occupied by light diverging surface structures 1 1 and 12 in recurrent patterns (schematically shown as thick bands) in which the structures are bands of width X ₂ and x ₄ respectively, separated by distances xi and x ₃ respectively and opposite patterns are mutually shifted by a distance y.

Figure 7 shows a cutting-edge view of a transparent sheet 30 with patterns according to Figure 6, for which x1 = x2 = x3 = x4 and y determines the angle of incidence θi for which none of the incident solar rays 10 is transmitted without interaction with either the structured bands 1 1 or 12.

Figure 8 shows the same transparent sheet with patterns of Figure 7, at the angle of incidence Θ2 for which part of the incident solar rays 10 is transmitted without interaction with either the structured bands 1 1 or 12.

Figure 9 shows a graph of the relative haze as function of the angle of incidence θ for the example of the transparent sheet of Figures 7 and 8, showing the maximum 13 and minimum 14 haze at angles corresponding to respectively Θ ₂ and Θ ₁ .

Most commonly greenhouses 50 are built preferably in a direction where the roof panels 1 and 2 are facing respectively east and west, as shown in Figure 1 . During the day the sun follows path 3 and for each position of the sun along this path the angle of incidence on the roof panels is different as illustrated in Figure 2 by the irradiation directions 7, 8 and 9 for respectively the positions of the sun 4, 5 and 6 in Figure 1.

The aim of the invention is to maximize the haze of the greenhouse 50 covering (roof panels 1 , 2) for the situation with the highest irradiation level, which is with the sun in mid-day position 5, and minimize the haze for the situation with the lowest irradiation level, which is with the sun in morning and evening positions 4 and 6. It is clear that these situations correspond with incident angles Θ ₁ and G ₂ on the flat roof panelsi , 2, that depend on the tilt angle of these panels 1 , 2, the orientation of the greenhouse 50 and the geographic position of the greenhouse 50 and that these angles can be calculated.

Using a transparent sheet 10 with two opposite surfaces 21 , 22 each partially occupied by light diverging surface structures 40 according to Figures 3 - 5, in which the in-plane dimensions of the structures are defined by Figure 6, it is shown by Figures 7 and 8 how the required angular dependency of the haze is obtained by the invention. Figure 9 illustrates the effect for different angles of incidence One example of an embodiment of the invention is a translucent sheet 30 of clear glass in which a pattern 40 according to figures 3 and 4 is etched on both sides, where the mutual displacement y is determined by the geographic position and orientation of the greenhouse 50.

Another example of an embodiment of the invention is a translucent sheet 30 of clear glass in which a pattern according to figure 5 is etched on both sides, again with the mutual displacement y determined by the geographic position and orientation of the greenhouse.

Another example of an embodiment of the invention is a translucent sheet 30 of clear glass in which a pattern of bands according to Figure 6 of diffusing structures is etched or rolled into both surfaces 21 , 22, again with the mutual displacement y determined by the geographic position and orientation of the greenhouse.

Alternatively (see Fig. 3B, 3C and 3D), the translucent device comprises two sheets 31 , 32 arranged parallel in which the first translucent sheet 31 comprises the first surface 21 and the second translucent sheet 32 comprises the second surface 22. In a preferred embodiment the first surface 21 and second surface 22 are arranged inside the space between the first translucent sheet 31 and the second translucent sheet 32 (shown in Fig. 3C and 3D) as in such an embodiment the space between the first and second translucent sheet 31 , 32 is unexposed to the outside and typically remains clean - ensuring the that the efficiency of the recurrent pattern 40 is maintained and not reduced due to the contamination of the pattern 40 by dirt.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

It should be apparent for a skilled person that the translucent device according to the invention may also comprise coatings for achieving well known additional effects, without departing from the scope of the invention. For example, optical coatings such as anti-reflection coatings or sunlight-shielding coatings or heat insulation coatings may be easily applied on the translucent device without altering the effect of the angular dependency of the haze generated by the translucent device. The additional coating may require an adaption in the absolute dimensions of the recurrent pattern to ensure that the exact anticipated angular dependency of the haze is achieved. This, however, is routine optical engineering to determine the effect of such an additional coating on the translucent device and is expected to be included in the current scope of protection.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. 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.