Abstract: Radiation-dose indicator as well as a lamp and a tanning apparatus comprising such a radiation-dose indicator.The invention provides a novel type of radiation-dose indicator which is reliable and accurate. The indicator comprises an optically active layer which includes a liquid-crystalline material as well as a radiation-sensitive compound. This compound is converted under the influence of radiation in such a way as to change the order of the liquid-crystalline material. Preferably, a trans-isomer is used as the radiation-sensitive compound, which is converted to the corresponding cis-isomer under the influence of radiation. In this way, the order of the liquid-crystalline material is broken. Indicators in accordance with the invention can very advantageously be used in UV- and IR-lamps as well as in tanning apparatus.

Abstract: The invention relates to an optical temperature indicator. The indicator comprises an optically active layer of a transparent polymeric material in which liquid-crystalline material is dispersed. The molecules of the liquid-crystalline material form part of a polymeric structure via covalent bonds, for example as side-chain groups. The polymeric structure is preferably based on a siloxane. Such an indicator exhibits a good mechanical stability, while the opacity is preserved for a long period of time.

Abstract: A molecularly oriented synthetic resin composition whose coefficient of linear thermal expansion in two mutually perpendicular directions, below the glass-transition temperature, is at least a factor of 3 smaller than in a third direction extending perpendicularly to the first two directions, is manufactured by curing a liquid-crystalline composition having a helicoidal order of molecules, so as to form a polymer network. The resins thus obtained are suitable for use as claddings on materials having a coefficient of thermal expansion which is smaller than that of most synthetic resins.

Abstract: An apparatus is provided (1) for preparing a hot beverage, comprising a water reservoir (3), means for removing and heating water from the reservoir and transferring it into a brewing chamber (5), and a light-transmissive jug (9) for catching hot liquid emerging from the brewing chamber (5), a wall (13) of the jug (9) being provided with optical means (15) for indicating the volume of liquid contained in the jug (9), wherein the optical means (15) comprise a first graduated scale (159) and a second graduated scale (153), the first scale (159) being clearly visible only when the jug wall temperature is below a reference temperature T.sub.o and the second scale (153) being clearly visible only when the jug wall temperature is above the reference temperature T.sub.o, whereby the reference temperature T.sub.o is within the range of 25.degree. C.<T.sub.o <80.degree. C.

Abstract: The invention relates to an illumination system (7) for a colour image projection device (1). The illumination system (7) comprises a radiation source (3) for generating an unpolarized radiation beam (5) and at least a cholesteric mirror (9, 10, 11, 12, 13, 14) for wavelength-selective splitting of the radiation beam (5) into at least two sub-beams of different wavelengths. A composite circular polarizer (35) for directly converting the unpolarized radiation beam (5) into circularly polarized sub-beams jointly forming one beam is arranged in the path of the unpolarized radiation beam (5) between the radiation source (3) and the cholesteric mirror (9). The composite circular polarizer (35) comprises a polarization-sensitive beam splitter (43) which splits the unpolarized radiation beam (5) into two mutually perpendicularly and linearly polarized sub-beams, and a polarization converter (51, 53; 59, 61).

Abstract: Picture inversion in display devices based on the twisted pneumatic effect is prevented by choosing a twist angle .phi.T such that 70.degree.<.phi.T<90.degree., and an angle .alpha. between the direction of polarization of one of the polarizers and the associated direction of orientation such that: 30.degree.+.phi.T/2<.alpha.<60.degree.+.phi.T/2.

Abstract: In a double cell the values of d..DELTA.n for both the actual cell (10) and the compensation cell (20) having opposite twist angles .phi. are chosen to be such that they are associated with different Gooch & Tarry extrema for a given wavelength. The compensation cell may then be thicker and can be obtained in a simpler manner. A universal compensation cell may alternatively be used.

Abstract: In a projection display device based on one or more (twisted nematic) LCDs (4), simple temperature compensation is possible by optimizing the d..DELTA.n value (n) at the maximal operating temperature. The associated transmission/voltage characteristics at different temperatures then extend substantially parallel so that it is possible to compensate for temperature changes by means of a simple voltage compensation.

Abstract: A liquid-crystal display device having an improved picture quality is obtained by rendering the iso-contrast curves rotationally symmetrical. This is obtained by means of a double cell construction, in which two identical TN-cells are present between two parallel polarizers, which TN cells are arranged relative to each other in such a manner that the director at the front face of the second cell encloses an angle of 180.degree. with the director at the front face of the first cell. A polarizer is provided between both cells, the direction of polarization of said polarizer extending perpendicularly to the direction of polarization of the two other polarizers.

Abstract: A liquid-crystal display device having a twisted nematic liquid-crystalline material is provided with a layer of an optically anisotropic material to obtain a colourless display device which is rich in contrast. The optically anisotropic material is a synthetic resin composition comprising a polymer network having a helicoidal order manufactured from a curable liquid-crystalline composition having a chiral dopant.