Controlling the distribution of the light emitted by adjustment of elements (reflectors with provision for adjusting the curvature F21V7/16; light filters or the like with provision for controlling the colour or intensity F21V9/40; screens using adjustable parallel laminae or strips F21V11/04; screens using iris-type diaphragms F21V11/10; screens using movable sheets without apertures F21V11/18; adjustable mountings for lighting devices F21V21/14)