PURPOSE: To secure a light source bearing stable high luminance in the intensity of light besides a small point exposure, by turning a long arc light source into a point source of light.

CONSTITUTION: A point light source part 5 is left behind at the part of a silica tube 4 corresponding to the central part of a luminous part 3 spanned between an electrode 1 at the high tension side and an electrode 2 at the earth side while a fine uneven surface is formed on a tube wall of the silica tube 4 by means of an abrasive and the like, and then a shading part 6 is formed with metals such as rhodium, etc., laid on the uneven surface, through which the unnecessary light of a long arc light source is intercepted by the shading part 6 and thereby the point light source part 5 is used as a point source of light. According to the above constitution, such a light source as being high luminance, stable light intensity and small in an illumination spot can be secured, leading to good cooling effects plus accuracy in the light source position so that there are following effects that lamp service life comes up by 1.2 times more than ever before while setting the light source position becomes facilitated and so forth.