Abstract: The luminaire comprises a cup-shaped reflector having facets which are curved continuously and extend from the light emanating aperture of the reflector towards the reflector axis. The facets of the reflector, in planes transverse to the reflector axis, are straight and constitute a regular polygon. The luminaire further comprises a circumferential light-absorbing collar which has a portion which narrows from the reflector edge in a stepwise manner. The luminaire together with an axially accommodated light source provides a wide, homogeneous, sharply bounded beam and at small angles with the axis. It is no longer observable as a source of light.

Abstract: Luminaire provided with a bowl-shaped reflector for an elongated light-emitting part of a light source to be arranged substantially on the principal axis of said reflector. The reflector has a reflecting surface composed of elongated facets whose longitudinal sides extend from adjacent the center to the peripheral edge of the reflector. The facets are concavely curved in a cross-section comprising the principal axis and are straight in a plane at right angles to the peripheral axis and constitute a regular polygon, the axis of symmetry of a facet extending in accordance with a curve approaching the shape of a parabola.

Abstract: A reflector whose reflecting surface is formed as a portion of a solid of revolution, the generatrix of the solid of revolution having a plurality of staggered parabolic segments, the transition portions located between the segments changing smoothly into the segments and being of such a shape that in use in the reflector, of a light source, the reflected light beam has a comparatively large width and that the object to be illuminated is illuminated uniformly.

Abstract: A color analyzer for determining the exposure time required for printing color photographs by an enlarger comprising a measuring unit having three photoelectric cells. The analyzer is further provided with a control unit being electrically connected to the measuring unit and having an electric circuit for determining the exposure time. According to the present invention, the characteristic values of the color components, blue, green and red are measured by a respective photoelectric cell for a test print as electric signals generated by the cells at voltages of S.sub.BO, S.sub.GO, and S.sub.RO at the associated exposure time t.sub.o. These values are stored in a memory and the exposure time t of an arbitrary picture is determined with the aid of measured signals S.sub.B, S.sub.G and S.sub.R for the components blue, green, and red. This determination is computed by way of the formula:t=3t.sub.o /[(S.sub.B /S.sub.BO)+(S.sub.G /S.sub.GO)+(S.sub.R /S.sub.RO)].