Abstract: Virtually all of the light reflected from an object to be inspected is made incident upon a focusing lens 7, a quantity of light in a regularly reflected light region on an plane P1 where an image is formed by a lens 7 is detected by a photodiode 8, while a quantity of light in a peripherally scattered light region is detected by a photodiode 9. If the quantity of light received (VDET1) in the regularly reflected light region is lower than a first reference value (VREF1) (S1=1), and the quantity of light received (VDET2) in the peripheral scattered light region is higher than a second reference value (VREF2) (S2=1), a determination is made that a defect is present.

Abstract: A low-pressure mercury resonance radiation source includes a discharge lamp containing mercury vapor and producing broad band radiation directly emitted from the mercury vapor through excitation of same by electric discharge, and a resonance cell containing mercury vapor and disposed adjacent the discharge lamp for absorbing the broad band radiation and reemitting narrow band mercury resonance radiation. The pressure of the mercury vapor within the resonance cell is controlled to a first predetermined value by controlling the temperature of a first mercury sump arranged within the resonance cell, and the pressure of the mercury vapor within the discharge lamp is controlled to a second predetermined value, preferably by controlling the temperature of a second mercury sump arranged in a side tube communicating with the discharge lamp.