Contrast for photos
In English, we learn to compare and contrast...or show the differences. In photography, contrast is important so that a pictures is not too gray...nor to BLACK/WHITE. Contrast is very subjective such that the SAME picture can be printed in a variety of ways. There are even special films, paper and camera settings and Photoshop (in the case of digital files) designed to improve contrast.
In the picture below (as seen on the door leading into the darkroom), the picture can be printed with a variety of contrast levels.
In the darkroom, you have a Contrast Control Knob and a Contrast White Light Lever. When the lever is disabled (pulled toward you...for focusing purposes as well as photograms, pinhole cameras and contact sheets), the enlarger will not increase the contrast. When you engage the Contrast White Light Lever, you will be turning on a filter that will make parts of the picture grayer or blacker and parts of the picture grayer or whiter, resulting in lower or higher contrast.
The Paper Selector Type should be set to the center position, or "Ilford".
When your enlarger is on, you will see the number illuminate.
Pull the lever toward you to DISENGAGE the filter. PUSH the lever AWAY from you to ENGAGE the filter.