on normal in the centre of film viewer).Īngle q Measured values Theoretical values 0 To verify the appliance of this law, some film viewers for industrial radiography have been verified to value the decrease of luminance intensity emitted in function of direction q tests made have given uniform results, as per example below in which luminous intensity = 1 for q=90° (e.g. A surface element that operates according to this law is called Perfectly Diffused. It must be considered that practically the intensity of a luminous source change according the different positions for many substances and practical situations the element luminous intensity can be stated in function of direction by the following relation: The steradiant is the subtended angle, in the centre of a sphere, from an area of arbitrary form with extension equal to the square of ray of the same sphere.
The luminance Intensity is measured in lumen per steradiant, unity is usually told Candle (Cd). Luminance Intensity: provided a luminous source S, its luminance intensity in the direction of ray's propagation direction is the relation I between the issued flux DF and the solid angle d w. CONTROL OF OPTICS CHARACTERISTICS: THEORETICAL PARTĭue to the complexity of this matter, it can be useful a little introduction to main quantities directly or indirectly used in optics measurements, because the recent norm EN 25580, as other previous norms, impose the execution of luminance measurements, different from others that want the characterisation of film viewers with illumination measurements. These norms do not settled any maximum value for radiographic density of films, but for its reading it must be used a film viewer according to UNI EN 25580 this condition is precisely indicated on UNI EN 1435, point 6.10. This matter presents renewed interest in the light of UNI EN 444 norm "General principles for radiographic examination of metallic materials with X and Gamma rays" and the following UNI EN 1435 "Radiographic Control of weld joints".
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The above mentioned specification, even if do not introduce substantial changes if compared to the ISO 5580 "Industrial radiographic illuminators - Minimum requirements", has shown some doubts for burdens related to its applications because of necessity, for functional test on film viewer, of measurements of optics luminance with expensive instruments and difficult to find and to calibrate. Giovanni Calcagno, Michele Murgia, Giuseppe OrlandoĪfter 2 years from the definition of UNI EN 25580 "Film Viewer for Industrial Radiography - Minimum requirements" is already possible to have a first balance concerning the application of the specification to a significant numbers of film viewers. General Characterisation of Industrial Film Viewers According to the UNI EN 25580 Standard.Characterisation of Industrial Film Viewers According to the UNI EN 25580 Standard
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