FIELD OF THE INVENTION

This invention relates generally to the field of surface lighting systems (such as floor lighting systems, wall lighting systems, or ceiling lighting systems), and in particular to a light-transmissive surface covering arrangement (such as a light-transmissive flooring arrangement, a light-transmissive wall covering arrangement, or a light-transmissive ceiling covering arrangement). The invention also relates to a light-emitting surface covering system comprising such a light-transmissive surface covering arrangement, to a method of modifying an inhomogeneity in light output of a light-emitting surface covering system, and to a method of providing a mask layer for a light-emitting surface covering system.

BACKGROUND OF THE INVENTION

Advances in lighting technology (notably for example advances in LED lighting technology) have enabled a range of new decorative and functional lighting applications. One particular application is that of surface lighting systems, such as ceiling, wall or floor lighting systems, in which lighting displays are incorporated within dedicated celing covering, wall covering or flooring arrangements to provide decorative effects or to communicate information to observers.

To ensure seamless incorporation of the lighting within the surface, source luminaires are typically installed in dedicated cavities or spaces behind the surface covering layer, such as beneath a floor covering layer. Light from the luminaire is transmitted through the surface covering layer to facilitate the illumination effects.

US-2011/203147 discloses a lighting arrangement having a carpet structure. The carpet structure has a lighting unit and a light transmissive carpet unit. The front face of the lighting unit is adjacent to the back side of the light transmissive carpet unit. The light transmissive carpet unit is arranged to transmit at least part of the light travelling in a direction from its back side to its front face.

One difficulty with this approach is that the optical properties of the light can often become distorted upon transmission through the surface covering layer. In particular, depending upon the physical and optical properties of the surface covering layer, the apparent intensity and/or colour of the output light can vary between different portions or regions of the surface covering layer.

It is an object of the present invention to reduce the luminous distortion of light patterns transmitted through the surface covering layer of a surface lighting system.

SUMMARY OF THE INVENTION

The inventors of the present invention have recognised that the distortion of light emitted from surface lighting systems may be caused by inhomogeneity in the optical transmissivity of the particular surface covering layer employed. For instance, if the surface covering layer is a floor covering layer, different colour patterns, yarn densities and height variations of carpet coverings or patterning or relief structures of vinyl or wood coverings may lead to a spatial variation in the light transmissivity of the floor covering layer. For similar reasons, a ceiling or wall covering layer may have a spatial variation in the light transmissivity. In such cases, even a perfectly uniform source illumination would fail to generate a uniform visible light output after transmission through the surface covering layer. Alternatively, such a surface covering layer intentionally may have a spatially

inhomogeneous transmissivity, e.g. in cases where the surface covering layer is designed to display a luminous image and/or message.

Embodiments of the invention seek to modulate, e.g. counter or amplify, the distortion in luminous output without limiting the freedom of design in selecting the surface covering layer.

The invention is defined by the claims.

According to a first aspect of the invention, there is provided a light- transmissive surface covering arrangement that comprises a surface covering element and a mask layer. The surface covering element has a first light transmissivity that varies as a function of position across the surface covering element, and the mask layer has a second light transmissivity that varies as a function of position across the mask layer. The first light transmissivity has a first spatial distribution across a first area of the surface covering element, and the second light transmissivity has a second spatial distribution across a second area of the mask layer. The second area of the mask layer is aligned with the first area of the surface covering element. For modifying an inhomogeneity in light output of a light-emitting surface covering system that comprises the aforementioned light-transmissive surface covering arrangement, either the second spatial distribution is inverse to the first spatial distribution to thereby reduce the inhomogeneity of light transmitted from the surface covering element, or the second spatial distribution mirrors the first spatial distribution to thereby amplify the inhomogeneity of light transmitted from the surface covering element.

The invention is based on the concept of utilising an auxiliary mask layer to modulate light before transmission through the surface covering element in a manner which takes account of a non-homogeneous transmissivity pattern of the surface covering element. By modulating the light before transmission through the surface covering element (as opposed to afterwards for instance), the mask layer may be hidden from view (i.e. behind or beneath the surface covering element).

By non-homogeneous light transmissivity, is meant a transmissivity which varies as a function of position across the mask layer or surface covering element. For instance, the surface covering element may be a flooring element that has a laminar construction, consisting of two opposing major surfaces. The transmissivity of the flooring element may vary as a function of position across the entity along directions parallel with one or both of these major surfaces. The mask layer likewise may have a laminar construction, defined by opposing major surfaces, the further non-uniform transmissivity varying as a function of position across the mask layer along directions parallel with one or both of these major surfaces.

Transmissivity means the effectiveness of the entity in transmitting radiant energy. It may for instance refer to the fraction of incident electromagnetic power that is transmitted through the body (at a given location). Transmissivity may be understood throughout this application as synonymous with transmittance for instance. The

transmissivity may be understood in the context of a number of embodiments (to be described below) as a wavelength-specific transmissivity, i.e. spectral transmissivity. Spectral transmissivity refers to the effectiveness of the entity in transmitting light of different wavelengths. A non-uniform spectral transmissivity may give rise to the appearance of colour patterning in the surface covering element.

The non-homogeneous second light transmissivity of the mask layer has a spatial distribution across the mask layer which matches at least a portion of the spatial distribution of the non-homogeneous first light transmissivity of the surface covering element. By this is meant that the transmissivity distributions across each of the mask layer and the surface covering element are congruent in terms of their spatial patterning across at least a portion of their areas (where patterning is to be understood broadly as including both regular and irregular patterning). For instance, the transmissivity of each of the mask layer and surface covering element may define a number of delineated regions of differing transmissivity. In this case, at least a portion of the respective regions of the mask layer and surface covering element may correspond spatially with one another, the boundaries of respective sets of regions mapping on to one another. In some cases, the spatially corresponding regions may have similar or corresponding transmissivity levels; in other cases they may have differing or complementary transmissivity levels.

In accordance with at least one set of embodiments, the non-homogeneous second transmissivity of the mask layer may be complementary to the non-homogeneous first light transmissivity of the surface covering element, such that, when aligned with the surface covering element, the non-homogeneous second light transmissivity at least partially counters the non-homogeneous first light transmissivity.

By 'complementary' is meant that the non-homogeneous second light transmissivity of the mask layer balances or opposes the non-homogeneous first light transmissivity of the surface covering element to thereby at least partly counter or offset the modulating effects of the surface covering element.

The non-homogeneous second light transmissivity of the mask layer may vary as a function of position across the mask layer in an inverse manner to the variation of the non-homogeneous first light transmissivity of the surface covering element. Regions of higher transmissivity of the surface covering element are thus arranged in opposition to regions of the mask layer having a lower transmissivity. The mask layer may thus be configured to reciprocally complement the transmissivity pattern of the surface covering layer and to thereby compensate for the non-uniform transmissivity to produce a resultant light output, upon transmission through a combination of the two layers, which is more homogeneous.

The term 'inverse' is not meant in a strict mathematical sense; it is to be construed as for instance synonymous with 'opposite'.

The non-homogeneous second light transmissivity of the mask layer may mirror at least a portion of the non-homogeneous first light transmissivity of the surface covering element to thereby amplify the inhomogeneity of light transmitted from the surface covering element.

The transmissivity distribution across the mask layer may substantially match or mirror that of the surface covering element such that spatially aligned regions of the mask layer and surface covering element have similar or identical respective transmissivity levels. Here, the transmissivity of the mask layer acts to reinforce or amplify that of the surface covering element.

The non-homogeneous second light transmissivity of the mask layer may be achieved in a number of ways.

In accordance with at least a first set of embodiments, the mask layer may comprise an optical filter. By optical filter is meant a layer which attenuates light to a particular extent, either through absorption or reflection of a portion of the light. The optical filter may be a frequency-specific filter, wherein the element is adapted to selectively transmit and/or attenuate only particular sets of frequencies of light. The optical filter may have a non-uniform transmissivity.

In particular examples, the surface covering element may have a non-uniform or non-homogeneous first spectral transmissivity, and said optical filter may have a nonuniform or non-homogeneous second spectral transmissivity, complementary to the first spectral transmissivity. By spectral transmissivity is meant frequency-specific transmissivity, wherein the surface covering element may exhibit a different transmissivity for different frequencies of light. The non-uniform or non-homogeneous second light transmissivity of the mask layer may compensate the non-uniform or non-homogeneous first light transmissivity of the surface covering element. An optical filter may be used to realise the non-uniform or non-homogeneous second spectral transmissivity.

In accordance with at least a further set of embodiments, the mask layer may comprise a non-uniform relief pattern to realise non-homogeneous second light

transmissivity. This may manifest in a non-uniform thickness of the mask layer, the thickness being a dimension extending at least partially orthogonally to a major surface of the mask layer and/or the floor covering element. By employing a non-uniform relief pattern (or thickness), the light transmitted across the mask layer travels through a greater or lesser amount of the material of the mask at different spatial locations across it. This may lead to a greater or lesser absorption of light by the mask layer through these different spatial locations, and hence a differing proportion of light transmitted.

The relief pattern may in examples vary in a step-wise manner across a surface of the mask layer to delimit a plurality of inset cavities within said layer.

In accordance with particular examples, the mask layer may be a planar layer. Typically the surface covering element will be planar or laminar and hence a correspondingly planar mask layer may ensure optimal coupling of light between the mask layer and the surface covering element. The mask layer may be comprised by the surface covering element. In this case there is no gap or separation between the mask layer and the surface covering element. The mask layer may be integrally comprised by the surface covering element, such that the two form a single cohesive body, or the mask layer may be joined or attached to the surface covering element. The mask layer may in further examples be at least partially embedded within the surface covering element.

In examples, the mask layer may be coupled to a light-receiving major surface of the surface covering element. The mask layer may be coupled so as to meet flush with the surface covering element.

In further examples, the mask layer may be incorporated within the body of the surface covering element. The two may be fully integrated in the sense that the surface covering element simply comprises masking material distributed within it which performs the function of non-homogeneously modulating light transmitted through the surface covering element.

In accordance with a further subset of embodiments, the mask layer may be spaced apart from the surface covering element, while remaining in optical communication.

In particular examples, the surface covering element is a floor covering element. In the context of this invention, a floor covering element is also simply referred to as a flooring element, which is to be understood as a finishing material for application over a floor surface to provide a walking surface. The flooring element may be a carpet flooring element, a PVC flooring element, or a laminate flooring element. A PVC flooring element is a flooring element that comprises (or is based on) polyvinyl chloride (PVC). A laminate flooring element is a flooring element that comprises (or is based on) laminate flooring tiles or panels, a laminate flooring tile or panel being a flooring product comprising a fused multi- layer structure.

In other particular examples, the surface covering element is a ceiling or wall covering element. The ceiling or wall covering element may comprise a material selected from the group consisting of plasters and wallpapers.

Alternative surface covering elements may comprise a material selected from the group consisting of paint, ceramic, paper, wood, plastic, textile, and vinyl.

According to a second aspect of the invention, there is provided a light emitting surface covering system, comprising:

a light transmissive surface covering arrangement in accordance with the first aspect of the invention; and a lighting assembly, arranged in optical communication with a light receiving surface of the mask layer, and operable to direct a light output onto the light receiving surface for transmission through a combination of the mask layer and the surface covering element.

The lighting assembly may be adapted, when in operation, to direct a homogeneous light output onto said light receiving surface of the mask layer. The transmissivity patterns of the mask layer and surface covering element act cooperatively to process the homogeneous light to provide a substantially homogeneous light output.

The lighting assembly may in examples comprise a plurality of light sources, each having independently controllable output intensity. This may add flexibility to the illumination of the surface covering arrangement.

According to a third aspect of the invention, there is provided a method of reducing inhomogeneity in light output of a light-emitting surface covering system, wherein the surface covering system comprises

a surface covering element having a first light transmissivity that varies as a function of position across the surface covering element, the first light transmissivity having a first spatial distribution across a first area of the surface covering element; and

a lighting assembly for directing a light output through the surface covering element;

wherein the method comprises the step of

modulating the light output in advance of reaching the surface covering element by means of a mask layer arranged between the lighting assembly and the surface covering element, the mask layer having a second light transmissivity that varies as a function of position across the mask layer, the second light transmissivity having a second spatial distribution across a second area of the mask layer, the second area of the mask layer being aligned with the first area of the surface covering element, and wherein either the second spatial distribution is inverse to the first spatial distribution to thereby reduce an inhomogeneity of light transmitted from the surface covering element, or wherein the second spatial distribution mirrors the first spatial distribution to thereby amplify an inhomogeneity of light transmitted from the surface covering element.

In order to provide a mask layer configured to effectively combine with the specific non-homogeneous transmissivity of a given surface covering element to achieve a desired output light effect, it may be necessary to fabricate each mask layer specifically for a given surface covering element. In some cases, the transmissivity properties of the surface covering element may be known in advance, in which case a mask layer may be produced based on these known properties and configured to counter or offset any inhomogeneity.

In further alternative cases, the particular transmissivity pattern of a surface covering element may not be known in advance. In these cases, it may be necessary to ascertain these properties in situ, through on-site examination of the optical transmissivity of the surface covering element after an initial provisional installation of the surface covering element.

In accordance with a fourth aspect of the invention, there is provided a method of providing a mask layer for a light emitting surface covering system, the light-emitting surface covering system comprising:

a surface covering element having a first light transmissivity that varies as a function of position across the surface covering element, and

a lighting assembly for directing a light output through the surface covering element;

and wherein the mask layer is for positioning in a light path between the lighting assembly and the surface covering element for modulating light en route to the surface covering element;

wherein the method comprises the steps of:

assembling the light-emitting surface covering system in the absence of the mask layer, such that the lighting assembly is in direct optical communication with the surface covering element;

activating the lighting assembly so as to direct light through the surface covering element;

controlling an image capture means arranged in front of the surface covering element (such as above a flooring element) to capture an image of a pattern of light transmitted from the lighting assembly through a first area of the surface covering element;

determining a first spatial distribution of the pattern of light transmitted through the first area of the surface covering element; and

forming a mask layer with a second light transmissivity that varies as a function of position across the mask layer, the second light transmissivity having a second spatial distribution across a second area of the mask layer,such that when the second area of the mask layer is positioned in alignment with the first area of the surface covering element, either the second spatial distribution is inverse to the first spatial distribution to thereby reduce an inhomogeneity of light transmitted from the surface covering element, or the second spatial distribution mirrors the first spatial distribution to thereby amplify an inhomogeneity of light transmitted from the surface covering element.

In accordance with this method of fabrication, the transmissivity properties of the mask layer are adapted based on observed transmission characteristics of the surface covering element. The pattern of light emitted from the surface covering element after transmission through the element of an initially homogeneous light source provides an indication of the particular pattern of transmissivity embodied by the surface covering element.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 schematically depicts a first example mask layer arranged in alignment with an associated flooring element;

Fig. 2 schematically depicts an example floor lighting system comprising a mask layer, a flooring element and a lighting assembly;

Fig. 3 schematically depicts an example light transmissive flooring

arrangement comprising a mask layer having a non-homogeneous spectral transmissivity;

Fig 4 schematically depicts an example floor lighting system comprising a mask layer having a non-uniform relief pattern; and

Fig. 5 schematically depicts a method of designing a mask layer for installing within an established floor lighting system to counter inhomogeneity in light output. DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a light-transmissive surface covering arrangement having a surface covering element with a non-homogenous first light transmissivity and a mask layer with a non-homogeneous second light transmissivity. The non-homogeneous second light transmissivity of the mask layer is based on the non-homogeneous first light transmissivity of the surface covering element such that when the two are appropriately aligned, a spatial distribution of the non-homogeneous second light transmissivity of the mask layer matches at least a portion of a corresponding spatial distribution of the non- homogeneous first light transmissivity of the surface covering element. In particular examples, the non-homogeneous second light transmissivity of the mask layer may be complementary to the non-homogeneous first light transmissivity of the surface covering element such that, when the mask layer is aligned with the surface covering element, the non-homogeneous second light transmissivity at least partially counters the non-homogeneous first light transmissivity.

In the remainder of this description, the invention is illustrated by means of examples wherein the light-transmissive surface covering arrangement is a light-transmissive floor covering arrangement, and wherein the surface covering element is a flooring element. It should however be understood that the invention is equally applicable to light-transmissive surface covering arrangements in the form of light-transmissive ceiling or wall covering arrangements, wherein the surface covering element is either a ceiling or wall covering element, such as a ceiling or wall covering element that comprising a material selected from the group consisting of plasters and wallpapers.

Fig. 1 schematically illustrates a first example mask layer 10, shown for purposes of demonstration stacked in alignment beneath an associated flooring element 12. The mask layer 10 and the flooring element 12 together define a light transmissive flooring arrangement 8 configured to co-operatively process an input light source to provide a substantially homogeneous light output.

The flooring element 12 has a non-homogeneous first light transmissivity. This is illustrated schematically in Fig. 1 by three regions of higher light transmissivity 16, 18, 20, surrounded by an encompassing region of low light transmissivity 24. The mask layer 10 is arranged beneath the flooring element and has a non-homogeneous second light transmissivity. This is illustrated schematically by three regions of lower light transmissivity 26, 28, 30, surrounded by a broader encompassing region of high light transmissivity 34. The mask layer 10 is aligned with the flooring element such that the three regions of lower light transmissivity 26, 28, 30 align optically with the three regions of higher light transmissivity 16, 18, 30 of the flooring element. Equally, the surrounding region of higher light transmissivity 34 is arranged to align optically with the broader region of lower light transmissivity 24 of the flooring element.

The mask layer 10 is hence configured such that when appropriately aligned with the flooring element (as illustrated in Fig. 1), it has a non- homogeneous second light transmissivity which varies as a function of position across the mask layer in an inverse or opposite manner to the variation of the first light transmissivity of the flooring element 12 arranged above it. Regions of higher light transmissivity 16, 18, 20 of the flooring element are aligned in opposition to regions of relatively lower light transmissivity 26, 28, 30 of the mask layer 10. In this way the mask layer acts to compensate or counter the inhomogeneity in light transmissivity of the flooring element, by ensuring that proportionately less light reaches regions of high transmissivity and proportionately more light reaches regions of lower transmissivity.

This effect is illustrated schematically in Fig. 2 which shows an exploded schematic view of a light emitting flooring system 40 comprising the flooring arrangement 8 of Fig. 1 and a lighting assembly 44 arranged beneath the mask layer 10, operable to provide a light output through the dual layers arranged above it. The black arrows in Fig. 2 illustrate the propagation of light through the arrangement, with larger arrows indicating light having a greater relative intensity or power, and smaller arrows indicating light of a lower relative intensity or power.

The lighting assembly 44 is configured to emit a light output onto a light receiving surface 48 of the mask layer 10 being substantially homogeneous in intensity across the extent of the surface. As illustrated in Fig. 2, upon transmission through the mask layer 10, the non- homogeneous second light transmissivity of the mask layer results in a modulation in the output intensity of the light. Portions of the light transmitted through the lower transmissivity regions 26, 28, 30 of the mask layer are modulated to have a

proportionately lower intensity; portions of the light transmitted through the surrounding higher transmissivity region 34 of the mask layer are modulated to have a proportionately higher intensity.

The modulated light output emitted from the mask layer 10 is subsequently received by an optically aligned receiving surface of the flooring element 12. Due to the complementary transmissivity patterns of the mask layer and flooring element described above, the modulated lower regions of light intensity arrive at the flooring element incident at the relatively higher regions of light transmissivity 16, 18, 20. Equally, the modulated regions of higher light intensity arrive at the flooring element incident at the region of relatively lower light transmissivity 24.

The flooring element 12 then optically processes the light in accordance with its own inhomogeneous light transmissivity, resulting in a further modulation of the light output. Due to the complementarity of the two transmissivity patterns, this secondary modulation effectively counters or offsets the inhomogeneity in light intensity induced by the mask layer 10, with regions of higher light intensity being attenuated to a greater extent and regions of lower intensity being attenuated to a lesser extent. This is illustrated schematically in Fig. 2 by the array of arrows extending from the upper surface of the flooring element. Upon transmission through the flooring element 12, the intensity of the light (indicated by the relative thickness and length of the arrows in Fig. 2) is substantially even across the extent of the flooring surface. Consequently, a substantially homogeneous light output results, despite the inhomogeneity in the transmissivity of the flooring element.

Although in the particular example of Figs. 1 and 2 the mask layer 10 is configured to counter or offset the inhomogeneity of the flooring element 12, in further examples, the flooring element may be configured to realise a different effect. In particular, in accordance with further examples, the mask layer may be provided with a transmissivity pattern or distribution which corresponds or mirrors that of the flooring element, rather than complementing it. In this case, the mask layer acts to reinforce or amplify the inhomogeneous transmissivity of the flooring element, rather than counter it. This may achieve interesting aesthetic effects, for instance enhancing the contrast or vividness of the intrinsic patterning of the covering layer by virtue of which the inhomogeneous transmissivity arises.

Reinforcement of the inhomogeneous transmissivity may be achieved simply by inverting the principles applied in the example of Figs. 1 and 2. A mask layer may be provided having regions of high transmissivity shaped and aligned to map spatially onto regions of high transmissivity of the flooring element, and vice versa. In this way the inhomogeneity is amplified.

The alternative option of reinforcement of the inhomogeneity, rather than the countering of it, may be applied in any embodiment or example described this application, including those outlined above, and those to be described below. In all cases, the effect may achieved in an analogous manner to that described above, simply by inverting the principle of countering the inhomogeneity by providing a mask layer having a transmissivity pattern which corresponds to or mirrors that of the flooring element.

Although in the particular example of Figs. 1 and 2, both the mask layer 10 and flooring element 12 are illustrated as planar (or laminar) elements, in alternative examples, these components may have a different particular topological structure. One or both may have a non-uniform topology, in the sense of incorporating or exhibiting an element of undulation or height variation. Where the flooring element comprises such non- flat topology, it may be advantageous for the mask layer to mirror or emulate the non-flat topology of the flooring element for reasons of optimal optical coupling. The mask layer 12 of the example of Figs. 1 and 2 is shown spaced apart from the flooring element 10, separated by an air gap. In alternative examples, the mask layer may be comprised by the flooring element. The mask layer may be integrally comprised by the flooring element, such that the two constitute a single unitary element (for instance where the material constituting the mask layer is dispersed within or layered atop the material of the flooring element during fabrication of the flooring element, see below) , or the mask layer may be coupled or attached to the floor element, for instance joined flush with a lower light receiving surface 50 of the flooring element (from the perspective shown in Figs. 1 and 2).

The mask layer 10 may in examples be printed onto said major light receiving surface 50 of the flooring element 12. The mask layer may for instance comprise a spectrally uniform light-attenuating layer. The layer may be printed with a greater density or thickness in regions where a lower light transmissivity is desired, and printed to a thinner or more sparse density (or even not at all) in regions where a greater light transmissivity is desired.

The printed layer may be a colour-specific layer. This might be of a uniform colour across all regions of the layer (for instance a neutral colour such as grey, with the object simply of achieving attenuation of light). Alternatively, different regions of the flooring element 12 may be printed with attenuating material of different colours, with the object for instance of offsetting or countering a spectral inhomogeneity in the light transmissivity of the flooring element 12 (i.e. where the flooring element comprises a degree of colour patterning).

In further examples, the mask layer 10 may be integrally incorporated within the body of the flooring element 12, for instance running through a central region of the body of the flooring element. In this case the two components may comprise a single integral component. Light-attenuating material may be dispersed through the body of the flooring element 12, for instance with varying concentration, e.g. greater concentration in regions where a lesser light transmissivity is desired, and lesser concentrations in regions where a greater light transmissivity is desired. Techniques to embed light attenuating particles within a suitable flooring element will be known to the skilled person.

In accordance with one or more examples, the mask layer 10 may be an optical filter. An optical filter is an element having the property of attenuating light to a certain degree. Different varieties of optical filter exist. A neutral density filter for instance induces a common degree of attenuation across all visible wavelengths of light. Such a filter may be used to apply a global attenuation of light intensity across the entire visible spectrum. The filter may be adapted to have a non-homogeneous transmissivity. For optical filters, this is typically quantified by an optical density of the filter, which denotes its degree of attenuation. A filter employed for the mask layer may have a non-homogeneous optical density.

Various optical filters will be known the skilled person, including polarising optical filters (which selectively transmit light according to the polarisation of the light), monochromatic filters, diachronic filters, long pass filters and short pass filters. Any variety of optical filter may be employed which may be adapted to provide the required non- homogeneous light transmissivity.

A frequency-specific optical filter may be used to compensate for inhomogeneity in spectral transmissivity of the flooring element 12. For instance, the flooring element may feature coloured patterning which results in differing attenuation of light depending upon the colour (or the frequency) of the light. This may result in colour-patterned light output. A mask layer 10 may be provided having a complementary non- homogeneous spectral transmissivity to compensate or counter the spectral non-homogeneity of the flooring element. Here, regions of the floor element of a first particular colour may be arranged in opposition to regions of the mask layer of a second, different colour, being selected such as to combine with the first colour to provide a third colour. Every colour region of the floor element may be optically coupled with a respective complementary colour region of the mask layer having a spectral transmissivity configured to realise said common third colour. In this way, a chromatic uniformity of light output may be achieved for light transmitted through a combination of the mask layer and the flooring element.

An example is illustrated schematically in Fig. 3 which shows a light- transmissive flooring system 8 comprising a flooring element 12 having a striped colour patterning. In particular, the pattern of the flooring element comprises five striped regions 62, 64, 66, 68, 70 each region having a different colour to any neighbouring region. The different colours are schematically represented in Fig.3 by differing shades of grey. Homogeneous light transmitted through the flooring element would acquire a colour patterning due to the differing spectral transmissivity intrinsic to each of the different coloured stripe regions 62, 64, 66, 68, 70.

To counter the colour patterning of the flooring element 12, the flooring system 8 comprises a mask layer 10 having a second colour patterning, reciprocal to the patterning of the flooring element. In particular, the mask layer comprises five striped regions 72, 74, 76, 78, 80, each having a different colour to any neighbouring region, and each being aligned in opposition to a respective region of the flooring element of a further colour, selected so as to combine with the colour of the mask layer to provide a third (common) colour. Thus, light transmitted in series through any opposing pair of striped colour regions is optically processed so as to provide a light output of the same, uniform colour. In this way, the colour patterning of the mask layer acts to counter the spectral inhomogeneity in the transmissivity of the flooring element, and realise a light output emitted from the flooring element which is substantially spectrally homogeneous.

The mask layer 10 of Fig.3 may, as described above, be a frequency-specific optical filter, adapted to exhibit a varying spectral transmissivity at different of the striped colour regions 72, 74, 76, 78, 80.

A non-uniform optical filter represents one way to achieve a mask layer having a non- homogeneous transmissivity. An alternative means may be to provide a mask layer 10 comprising a light attenuating material, and being shaped to have a non- homogeneous relief pattern across one or both of its major surfaces. A thickness of the layer may for instance vary. The non-homogeneous relief pattern may vary in a smooth or continuous manner as a function of position across the layer, or it may vary in a discrete, step-wise manner, to thereby define a plurality of sharply defined cavities (or protrusions) of possibly differing depths.

An example is illustrated schematically in Fig. 4, which shows a light-emitting flooring system 40 comprising a mask layer 10 having a plurality of cavities 92, 94, 96 inset within a lower light receiving surface 48. A flooring element 12 having a non- homogeneous first light transmissivity is coupled across an upper surface of the mask layer. The

inhomogeneity of the flooring element is represented schematically in Fig. 4 by a plurality of differently shaded regions 98, 100, 102, each representing a region of the flooring element 12 of a differing transmissivity. A lighting assembly is arranged beneath the mask layer 10, the lighting assembly comprising a plurality of light sources 110, each being operable to emit a light output of a common intensity in the direction of a light receiving surface 48 of the mask layer.

The mask layer 10 comprises a set of three cavities, a central cavity 94 of a first height, and two surrounding cavities 92, 96 of a second, smaller height. The cavities thus vary the thickness of the mask layer at different sections of the layer, each being aligned with a different respective section 98 of the flooring element 12, having a differing transmissivity.

By varying the thickness or relief of the mask layer 10 in this way, light transmitted through the layer at different points is induced to pass through differing amounts of the attenuating material which constitutes the layer. Hence regions of higher relief will result in greater attenuation of light (i.e. lower transmissivity) and regions of lower relief less attenuation of light (i.e. greater transmissivity). By appropriately varying the relief pattern, a mask layer having any desired variation in transmissivity as a function of position may be achieved.

In the example of Fig. 4, the region of lowest thickness of the mask layer (defined by cavity 94) is aligned with a central region 100 of the flooring element 12 having lowest relative light transmissivity. The two surrounding regions of the mask element 10 having second lowest thickness (defined by cavities 92, 96) are aligned with the two regions of second greatest transmissivity 98, 102 of the flooring element. Hence light transmitted through the mask layer 10 is attenuated least (so results in greatest relative intensity) for light directed onto region 100 of the floor element and attenuated most (so resulting in lowest relative intensity) for light directed onto regions 98, 102. In this way, the non-uniform thickness of the mask layer acts to counter the inhomogeneous transmissivity of the flooring element by modulating the light proportionately for regions of different transmissivity of the flooring element.

In the example of Fig. 4, the cavities (92, 94, 96) defined by the non-uniform relief pattern are shown as empty recesses in the mask layer. However, in further examples, the cavities may be filled with a transparent filler material so as to provide a flat lower light receiving surface 48 for the mask element. This may both increase rigidity of the mask and render mounting of the mask layer within an encompassing flooring arrangement easier.

The flooring element 12 may be any variety of light transmissive flooring element and may, by way of non-limiting example, comprise a carpet layer, linoleum, vinyl, wood, or any other suitable flooring material.

The flooring element may in particular examples comprise dedicated light exit windows to allow escape or passage of light with minimal attenuation. The windows may be specially shaped to provide a decorative effect or to enable communication of information. The light exit windows may for example be regions of extreme high light transmissivity. The light exit windows may in examples be shaped to communicate worded messages, or to communicate information via symbols or other pictorial representation (e.g. arrows indicating a direction of travel).

The lighting assembly 44 may be adapted, when in operation, to emit a substantially homogeneous light output onto the light receiving major surface 48 of the mask layer 10. The lighting assembly may have a panel- like construction, as illustrated in Fig. 2, comprising a planar light exit surface from which is emitted a substantially homogeneous light output being directed evenly across the receiving surface of the mask layer. The lighting assembly may in examples comprise a plurality of light sources, where these optionally may include or consist of LED light sources. The plurality of light sources may have

independently controllable output intensity. Any alternative light sources may also be used such as alternative solid state light sources, fluorescent light sources or incandescent light sources.

The lighting assembly 44 may have a different structural configuration to that illustrated in Fig. 2. The lighting assembly may comprise a single, central lighting element having for instance a hemispherical light output surface. The lighting assembly may comprise an array of light sources operated in unison to provide the light output onto the mask layer 10.

In accordance with any embodiment, the light output generated by the lighting assembly 44 may be a static light output or a dynamic light output. A dynamic light output enables creation of moving or changing light effects using the floor lighting system, for instance scrolling text or moving images.

In order to provide a mask layer 10 configured successfully to counter the particular non- homogeneous first light transmissivity pattern of a given flooring element 12, it may be necessary to fabricate each mask layer specifically for any given flooring element. In some cases, the transmittance properties of the flooring element may be known in advance, in which case a mask layer may be produced, based on these known properties, so as to counter or offset any inhomogeneity. The mask layer might be manufactured and distributed jointly with the flooring element for which it has been designed, the two being provided together as co-functioning unit. Alternatively, a particular variety of mask layer may be manufactured for a specific model or variety of common flooring element, and may be sold and shipped separately for incorporation within floor lighting systems.

In some cases however, the particular transmissivity pattern of a flooring element 12 may not be known in advance for example where there are wide tolerances in the manufacture process, leading to variation in the optical properties of different batches of a given flooring element. It may also not be known in advance the exact relative alignment or positional relationship between the lighting assembly 44 and the flooring element, which may affect the distribution of light onto the flooring element and hence the luminous

characteristics of the flooring arrangement. In these cases, it may be necessary to ascertain these properties in situ, through on-site examination of the optical transmissivity after an initial provisional installation of the flooring element. Accordingly, examples in accordance with a further aspect of the invention provide a method of fabricating a mask layer 10 for a light emitting flooring element 12 having a non-homogeneous second light transmissivity being suitably complementary with said flooring element to counter the non-homogeneous first light transmissivity of the flooring element. The method comprises examining the optical transmittance properties of the flooring element under homogeneous illumination, and on the basis of the results, fabricating a dedicated mask layer being adapted to counter any inhomogeneity.

A first stage of the method is illustrated schematically in Fig. 5. A light transmissive flooring element 12 is installed or at least provisionally mounted in optical communication with a source lighting assembly 44. The lighting assembly is controlled or operated to direct a homogeneous light output through a light receiving surface of the flooring element. The light is transmitted through the body of the flooring element and modulated by the non-homogeneous first light transmissivity of the element. This non- homogeneous light transmissivity is illustrated schematically in Fig. 5 by three higher light transmissivity regions 16, 18, 20, surrounded by an encompassing region of lower light transmissivity 24.

Light transmitted through the flooring element 12 is differently attenuated by the different regions of the element, resulting in a non-homogeneous light output being emitted from the surface of the element. This is illustrated schematically by the black arrows, which indicate light propagation, with larger arrows denoting light of greater light intensity or power and smaller arrows denoting light of lower intensity or power.

An image capture means 52 (a camera in the example shown in Fig.3) is arranged above the flooring element 12 with the flooring element within its field of view. Upon activation of the lighting assembly 44 and transmission of light through the flooring element, the camera 52 is controlled to capture an image of the light output pattern emitted from the surface of the flooring element.

The captured image is then analysed to determine an intensity distribution pattern of the light output (i.e. to derive a function or representation of the variation of intensity of the light output as a function of position across the surface of the flooring element).

Based on the derived spatial intensity distribution, the transmissivity pattern of the flooring element 12 may be determined. Since the light emitted by the lighting assembly 44 is assumed to be homogeneous, any inhomogeneity in the transmitted light output may be attributed to inhomogeneity in the transmissivity of the flooring element. In particular, the non-homogeneous first light transmissivity of the flooring element may be assumed to be proportionate to the spatial intensity variation of the captured light output (since regions of higher light output will be caused by transmission of light through regions of higher light transmissivity).

Based on the captured light output, a mask layer having a non-homogeneous second light transmissivity complementary with the non-homogeneous first light transmissivity of the flooring element may be designed and manufactured. In particular, a mask layer may be fabricated having a transmissivity pattern representing an inverse of the spatial intensity distribution pattern of the captured light output. Since (as explained above) this distribution is reflective of the transmissivity pattern of the flooring element 12, by providing a mask layer having an inverse variation in transmissivity as a function of position , the mask layer will function to counter or offset the variations in the flooring element. In particular, spatial regions of the flooring element having a higher light transmissivity will, when the flooring element is appropriately aligned with the mask layer, be arranged in opposition to regions of the fabricated mask layer having a lower light transmissivity.

The method of Fig. 5 may hence be applied to produce a mask layer for retrospective installation within a floor lighting system which has already been at least provisionally installed.

Methods of fabricating a mask layer having a desired non-homogeneous second light transmissivity will be known to the person skilled in the field. Different options for realising the mask layer have been discussed above including spatially non-uniform optical filters and spatially varying relief patterns. It will be apparent to the skilled person from these discussions, and calling upon relevant teachings of the common general knowledge, suitable means for fabricating a mask layer having an arbitrary desired light transmissivity pattern configured in accordance with the captured light output pattern.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.