Abstract: The invention relates to an air-purifier comprising a insulating disc (9), which is placed inside a housing (6) on one side thereof and which has openings (10), and comprising an insulating end wall which is located on the other side of the housing (6) and which is provided with perforations (4). In addition, supporting tubes (8), which are parallel to the axis of the housing (6), and control electrodes, which are provided with a positive and negative charge, are placed inside said housing (6). The invention is characterized in that: the electrode system is placed inside the supporting tubes (8); the supporting tubes (8), on portions of their lateral surfaces located opposite the end wall (5), are encircled by a screen (7) that has a low air resistance, and; the space between the supporting tubes (8) is filled with filter insert means (16).

Abstract: A lighting apparatus is provided having a plurality N of light sources arranged annularly around the optical axis of a reflector. The efficiency of such an apparatus and its service life are improved by providing a central mirrored column which is symmetrically disposed with respect to the light sources. The column has C.sub.N or D.sub.N symmetry and reflects light emitted by the light sources away from the light sources themselves, thereby reducing the amount of light reflected back at the light sources and reducing their thermal load. The column has peaks that extend into the notional annulus on which the light sources are arranged to shield adjacent light sources from each other.

Abstract: An apparatus for the testing of spheres for geometric exactness, which comprises a light source, a projectable image within or outside of said light source, optical means for simultaneously directing light in two different directions wherein one of said directions is onto a sphere to be tested and the other of said directions in onto an imaging means, and means for directing light onto said imaging means either as reflected from the sphere to be tested, or both from the sphere and from the light source without the optical interposition of the sphere.

Abstract: A light source having a single glass bulb housing and a multiple of three electrically interconnected fluorescent tubes. The tubes are located outside of the focal point of a smooth curved mirror. The phases of the fluorescent bulbs are electrically overlapped so as to substantially eliminate flickering of the light and to maximize the light intensity.This is a file wrapper continuation of application Ser. No. 166,783, filed Mar. 2, 1988; which is a file wrapper continuation of application Ser. No. 859,614, filed on May 5, 1986, both now abandoned.