Many of the natural-world depth specifiers are either not available in flat screen electronic images, or, as with `brightness,' conflict with other information in such images that does specify depth. Depicted distance changes within the electronic scene do not affect the illuminance of the retinal image as would a change of distance in the natural world. Studies to be reported suggest that luminance differences between objects can significantly modulate the information from linear perspective, and hence the electronic image itself may contain the potential for conflict between `depth cues.' Subjects were required to judge relative distances between pairs or triplets of objects with either consistent or inconsistent luminance gradients, in scenes containing varying amounts of depth information such as perspective, presence or absence of a horizon, etc. The direction of the gradients significantly affected judgments in all cases. Further studies required subjects to move an object in the simulator display and align it with static objects in the display. The results were consistent with the static scene data. Explanations considered are: the Irradiation Phenomenon, as applied to both humans and electronic displays, and luminance gradient or contrast gradient effects. As well as the luminance effects, there were also individual differences in accuracy of judgments as related to a measure of spatial ability, (the Shapes Analysis Test). The practical implications are discussed.