Abstract: There is provided a light source consisting of at least one flexible, cable-like electroluminescent filament, each filament having a central electrode (2) surrounded by an electrically insulating dielectric layer (4), and a layer (6) consisting of a mixture of an electroluminophor powder and a binder. The mixture is applied to the dielectric layer (4). The light source also includes a transparent electrode (8) surrounding the mixture layer (6). Pores formed in the mixture layer (6) are filled in by a transparent filler substance. A method for preparing the light source is also provided.

Abstract: A cable-like electroluminescent light source comprises at least two electrodes mutually disposed in such a way as to create between them an electric field when a voltage is applied to them; at least one type of pulverulent electroluminophor dispersed in a dielectric binder and disposed in such proximity to the electrodes as to be effectively excited by the electric fields when created and to emit light of a specific color, and a transparent polymer sheath encasing the electrodes and the electroluminophor.

Abstract: A constant-deviation device is disclosed which comprises a first reflective element in the form of one or more roof prisms and one or more second reflective elements providing one or more reflections. The first and the second reflective elements are mutually adjustable by rotation about one or more axes thereby to set an angle between the incident and the exiting beam. In one or more planes the angle is substantially unaffected by changes in the direction of incidence of the incident beam.

Abstract: There is provided an apparatus for measuring the refractive index of fluids. The apparatus comprises a substantially U-shaped sensor rod made of a transparent material and is submersible in the fluid. The bent portion of the sensor rod has a diameter of curvature at least two times larger than the diameter of the sensor rod, and chosen so as to optimize sensitivity for a given range of indices. The two ends of the U-shaped sensor rod are connectable to a housing and a light source inside the housing has optical access to the face of one of the sensor-rod ends. A light detector means also disposed inside the housing has optical access to the face of the other one of the sensor rod ends.

Abstract: A sensor for use in aligning a solar collector system wherein the sensor includes a radiation detector providing signals responsive to impinging radiation and means for focusing the radiation into an astigmatic image positioned on the detector when the system is misaligned.