The examination of the finished radiograph should be made under conditions that favor the best visibility of detail combined with a maximum of comfort and a minimum of fatigue for the observer.

To be satisfactory for use in viewing radiographs, an illuminator must fulfil two basic requirements.

It must provide light of an intensity that will illuminate the areas of interest in the radiograph to their best advantage, free from glare.

It must diffuse the light evenly over the entire viewing area. The colour of the light is of no optical consequence, but most observers prefer bluish white. An illuminator incorporating several fluorescent tubes meets this requirement and is often used for viewing industrial radiographs of moderate density.

For routine viewing of high densities, one of the commercially available high-intensity illuminators should be used. These provide an adjustable light source, Exposure conditions should be such that the total density of the radiograph (including base and fog density) in the inspected area is greater than or equal  2 .0  for class A  and  2.3 for Class B .the maximum intensity of which allows viewing of densities of 4.0 or even higher.

Such a high-intensity illuminator is especially useful for the examination of radiographs having a wide range of densities corresponding to a wide range of thicknesses in the object. If the exposure was adequate for the greatest thickness in the specimen, the detail reproduced in other thicknesses can be visualized with illumination of sufficient intensity.

The contrast sensitivity of the human eye (that is, the ability to distinguish small brightness differences) is greatest when the surroundings are of about the same brightness as the area of interest. Thus, to see the finest detail in a radiograph, the illuminator must be masked to avoid glare from bright light at the edges of the radiograph, or transmitted by areas of low density. Subdued lighting, rather than total darkness, is preferable in the viewing room. The room illumination must be such that there are no troublesome reflections from the surface of the film.