An X-ray film viewer, also known as a negatoscope or X-ray illuminator, is a medical device that allows users to view X-ray films in detail. They are used in a variety of medical and industrial settings to help technicians, radiologists, and physicians interpret X-ray images for diagnosis, quality control, and product integrity. 
Here are some characteristics of X-ray film viewers:
Light source
X-ray film viewers use a bright light source, such as fluorescent or LED lamps, to illuminate the X-ray film from behind. 
Brightness
The brightness of the light is usually variable so that users can adjust it to get the most precise information. 
Illuminated surface
The illuminated surface should be homogeneous, meaning that all areas are adequately illuminated. 
LED technology
LED X-ray film viewers are efficient, have a long lifetime, and consume low energy. 
Panel options
Some X-ray film viewers are available with single, double, triple, or quadruple panels.