Abstract: Retroreflective prism sheeting is formed in a mold with textured facets and/or windows thereon. Smaller prisms are formed adjacent larger prisms. Optionally, the optical axis of the prisms may be tilted with respect to one another, preferably in a negative direction. The textured facets or windows provide more uniform retroreflected light intensity distribution and whiteness of the sheeting.

Abstract: Anti-counterfeiting marking for documents, which marking may be disguised as an incidental or artistic feature of overall marking on the documents is adapted to be read by a complementary reading device. In one embodiment the marking may be a one, two or three-dimensional statistically fractal marking and is representative of an array of digits in which the value of each digit is represented by the fractal dimensions over a corresponding region or set of regions of the document bearing the marking. Corresponding apparatus for reading the anti-corresponding marking is also provided.

Abstract: A light diffusing screen is made by exposing a photopolymerisable material to polymerising light through a mask having an array of light-transmitting apertures in an opaque background or vice versa, at least some of the light being directed obliquely onto the photopolymerisable material. The resulting photopolymerised material has asymmetric light diffusing properties. In some embodiments two beams of light directed onto the photopolymerisable material are equally and oppositely inclined to the perpendicular to the plane of the material. An analogous effect may be provided, in other embodiments, by exposing the photopolymerisable material to light converging conically on the photopolymerisable material.

Abstract: Retroreflective prism sheeting is formed in a mold with textured facets and/or windows thereon. Smaller prisms are formed adjacent larger prisms. Optionally, the optical axis of the prisms may be tilted with respect to one another, preferably in a negative direction. The textured facets or windows provide more uniform retroreflected light intensity distribution and whiteness of the sheeting.

Abstract: Retroreflective prism sheeting is formed in a mold with textured facets and/or windows thereon. Smaller prisms are formed adjacent larger prisms. Optionally, the optical axis of the prisms may be tilted with respect to one another, preferably in a negative direction. The textured facets or windows provide more uniform retroreflected light intensity distribution and whiteness of the sheeting.

Abstract: Various combinations of different optical features in a microlens screen are disclosed. In one arrangement, a screen is provided for depixelating purposes, comprising an array of transparent rectangular portions (14) in a light diffusing field (20) formed by minute closely packed microlenses of a graded refractive index type. In another arrangement, a screen formed with an array of integral graded refractive index lenses has surface refractive index lenses additionally provided by part-spherical embossments on a surface of the screen, the embossments being of one or more orders of magnitude greater in diameter than the graded refractive index lenses. There are also disclosed techniques for preventing light transmission through a microlens screen except through the microlenses, the use of microlens screens to improve the performance of solar panels and microlens screens conforming to a part-spherical surface.

Abstract: In the manufacture of a screen suitable for use as a rear projection screen, a first layer (10) of a photopolymerisable monomer or oligomer which is tacky in its monomeric or oligomeric form and non-tacky in its polymerised form, is exposed to polymerising light, such as ultra-violet light, in a pattern comprising an array of spots of such light, and consequent selective polymerisation is allowed to take place in the first layer (10). There is then applied to the exposed surface of the first layer (10) a printing medium comprising an opaque pigment layer (28) on a supporting substrate (30) so that the pigment layer (28) contacts the exposed surface of the first layer (10) and sticks to the unpolymerised and therefore still tacky regions of the first layer (10), but not to the polymerised regions. The substrate (30) carrying the pigment layer (28) is then stripped from the first layer (10), leaving pigment (28) adhering only to the unpolymerised regions.

Abstract: A progressive method of writing a long grating in a substrate using a pulsed interference fringe pattern. The substrate is moved through the fringe pattern while being continuously illuminated with light of a different wavelength to produce a diffracted beam whose phase is monitored to produce a control signal that regulates the pulsing of the writing beam to ensure that the fringe pattern is present only when it is in correct registry with the grating being written.

Abstract: A mask through which a sheet or layer of a photopolymerizable monomer can be exposed to polymerizing light is manufactured by placing a fiber optic plate, or a ground glass plate or the equivalent over the emulsion layer of a photographic plate and exposing the photographic emulsion, through the fiber optic plate or ground glass plate, by a laser beam scanned across the plate in a raster. By this technique, there is produced, over the photographic plate, a random speckle pattern of substantially the same density and intensity over the whole plate.

Abstract: An image display arrangement comprising a collimating fibre-optic plate arranged to be illuminated from one side, for example a fibre optic plate forming the screen of a c.r.t. display tube and coated with a phosphor for providing such light, has, on at least one side thereof a layer of a photopolymer having formed therein an array of integral graded refractive index lenses, each extending over and in register with the end face, adjoining the photopolymer layer, of a respective optic fibre of the fibre optic plate. Each said graded refractive index lens is of a power such as to enhance the collimating effect of the respective optic fibre. A diffusion layer is preferably superimposed on the photopolymer layer, to impart a controlled diffusion to light passing through the optical fibres and said photopolymer layer, such as to render invisible or less visible the regions, in the fibre-optic plate, between adjoining optical fibres. The invention thus reduces or eliminates the so-called "chicken wire" effect.