Spatial comparison of lights from a local area will reveal the details of the objects of interest while the absolute light intensity will mostly represent the illumination condition which is usually not of interest.

Examples:

As an example for spatial comparison, consider the screen of a TV set or a computer monitor, which, when turned off, looks gray in a normally lit room. But after it is turned on, the darkest areas on the screen look black compared to the brighter areas, although they emit no less light than before.

As an example for temporal compariosn, dip your right hand in cold water before dipping both hands in warm water. The warm water will feel hotter to the right hand than to the left.

A direct implication of center-surround RF structures of the cells in the visual cortex is that they will only respond to signals with local (within the RF) intensity difference. Therefore a local area of uniform intensity will cause little or no response from these cells. This means that a sizable visual object will be responded to only by those cells with their RFs covering the boundary, but not those cells which cover the interior of the object, although we vividly see the interior. Seemingly counter-intuitive, but this may be how the brain encodes visual information as this is the most efficient way to do so. Imagine what a 3-year-old will do when asked to draw a car.