Abstract: An emitter and a receiver in a light barrier system are aligned by placing one or more retroreflective elements in a vicinity of the receiver such that a beam of visible light emitted by an optical alignment element impinges on a retroreflective element when the light beam emitted by the emitter impinges on the receiver. The optical alignment element is activated to emit a beam of visible light, and optical components of the system are adjusted so that the visible beam emitted by the optical alignment element impinges on, and is reflected by, the retroreflective element.

Abstract: An optoelectronic device, e.g. of a photocell or light barrier, comprising an electrical-to-optical or optical-to-electrical transducer, and an optical tube assembly comprising an optical chamber, a first aperture proximal with respect to the transducer, and a second, distal aperture being formed in chamber wall. In at least one first half-section taken e.g. along optical axis, at least an intermediate portion of the chamber wall extending between a first and a second line has a local tangent at each point (P) oriented so that any stray light ray incoming from the boundary point of the first aperture in the opposite half-section would be so deviated at that point (P) as to impinge upon the chamber wall at an impingement point (Q) in said first halfsection and more distal than the distal line.

Abstract: An optoelectronic device, e.g. of a photocell or light barrier, comprising an electrical-to-optical or optical-to-electrical transducer, and an optical tube assembly comprising an optical chamber, a first aperture proximal with respect to the transducer, and a second, distal aperture being formed in chamber wall. In at least one first half-section taken e.g. along optical axis, at least an intermediate portion of the chamber wall extending between a first and a second line has a local tangent at each point (P) oriented so that any stray light ray incoming from the boundary point of the first aperture in the opposite half-section would be so deviated at that point (P) as to impinge upon the chamber wall at an impingement point (Q) in said first halfsection and more distal than the distal line.