Optical: systems and elements – Diffusing of incident light
Reexamination Certificate
1999-03-26
2001-08-14
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Diffusing of incident light
C359S707000, C349S062000, C349S064000, C362S035000
Reexamination Certificate
active
06275339
ABSTRACT:
The present invention relates to an edge-lighted luminous device.
The technical field of the invention is the field of manufacturing luminous display devices.
BACKGROUND OF THE INVENTION
It is known that luminous display devices such as signs having symbols and/or graphics elements such as images can be made out of a thin support or substrate which may be plane, such as a sheet or a panel of translucent or transparent material, and which is lighted via the edge of the support by means of a light source such as a fluorescent tube; one of the main faces of the support may have zones of shapes that correspond to symbols (digits or letters in particular) which are etched or frosted by sand-blasting so as to appear brighter than the remainder of the main face of the support.
The problem encountered in that type of device is the problem of non-uniform lighting: zones far away from the light source are darker; it also often happens that shadows can be seen that the frosted zones cast into other zones of the support.
Pat. No. EP 549 679 describes a sign comprising a light-transmitting sheet which is side-lighted and which has two opposite faces each having dots applied thereto; according to that document, in order to obtain regular lighting of the sign, the dots are etched, painted, or printed, and form a matrix substantially covering the two main surfaces of the sheet; nevertheless, it has been observed that that technique does not provide entire satisfaction.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide an edge-lighted luminous device which is improved, and also a method of manufacturing such a device.
The solution to the problem posed consists in providing, on at least one of the two main opposite faces of the light-transmitting support (such as a sheet or plate of translucent or transparent plastics material), a grating of linear diffusing motifs, i.e. motifs that are elongate along a straight or curved line, and with spacing that varies regularly in geometric progression.
In another aspect, the invention consists in proposing a light guide for a lighting device, the light guide comprising (or being constituted by) a transparent (plane or curved) plate of glass or plastics material having two opposite main faces and an edge, at least one of the main faces including a grating of linear diffusing motifs (to enable said main face to emit light conveyed by the plate); the spacing of the linear diffusing motifs varying regularly along an axis in geometric progression having a ratio situated in the range 0.99 to 1.01.
The diffusing nature of the motifs results from the outside face of the support being deformed locally either to be in relief or preferably to be recessed; because this deformation extends uniformly and identically all along the linear motif, light travelling inside the support is caused to be diffused and/or extracted in a manner which is uniform all along the linear motif; because the linear motifs are spaced apart by a distance that varies regularly (i.e. that increases or decreases regularly) along an axis passing through the light source and/or perpendicular to the edge of the support, diffusion is obtained which is uniform over the entire zone of the support that contains the linear diffusing motifs.
In a preferred embodiment, the linear diffusing motifs are constituted by segments which may be curvilinear but which are preferably rectilinear, which motifs are etched and/or recessed, i.e. they constitute grooves; the various linear motifs or grooves are preferably identical in width, and the spacing between the linear motifs varies in geometric progression having a ratio of the order of 0.99 to 1.01, and preferably of the order of 0.999 to 1.001, and in particular of the order of 0.9999 to 1.0001, but not equal to 1.
The spacing of the motifs increases on coming closer to the edge via which light is injected into the support; the invention makes it possible to obtain brightness that is substantially constant over all of the zone of the substrate that is provided with linear diffusing motifs; this zone can consist in and/or extend over a substantial portion of the main face, e.g. over all of at least one of the two opposite main faces, so that luminosity is uniform over the entire face; under such circumstances, for the purpose of making a sign, the symbols to be displayed are written either on the face of the support that carries the linear diffusing motifs, or else on a separate medium, such as a sheet of paper, which is pressed against the face of the support provided with the linear diffusing motifs; alternatively, the linear motifs are disposed regularly in a zone whose (outer or inner) outline corresponds to the shape of the symbol or drawing to be displayed; in which case, the ends of the segments of the linear diffusing motifs are situated on said outline forming the envelope of the symbol.
When the support is lit via one edge only, the spacing of the motifs varies monotonically, decreasing going away from said edge; when the support is lit via two opposite edges thereof, the spacing of the diffusing motifs varies in non-monotonic manner: decreasing going away from a first edge towards a central zone of the support, and then increasing going away from said central zone towards a second lighting edge opposite said first lighting edge.
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Blanc Christophe E.
Chazallet Frederic
Ladas & Parry
Nguyen Thong
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