If you were to shine a flashlight on one side of your face there would be differences in the pattern of light and darkness across your facial features. This would be an example of:

Contrast, is the right answer.

Explanation:

The difference in color or luminance that makes an object separable is known as Contrast. In the context of the real-world visual perception, it is defined by the variance in the color and shine of the object and other articles within the corresponding area of view. Contrast sensitivity is one of the most significant measures of visual function, particularly in the situation of fog, glare or low light.