Control system and methods for multi-mode privacy display

A display apparatus comprising:

• a display device arranged to display an image and capable of operating in at least a first mode and a second mode, wherein the image remains visible in both the first mode and the second mode in an on-axis direction, and a visibility of the image is reduced in an off-axis direction in the second mode compared to the first mode;
• and
• a control system arranged to control the display device, the control system being capable of selectively operating the display device in the first mode or the second mode, wherein the control system is arranged to selectively control luminance of the displayed image in the first mode based on a first function that relates a level of luminance to a detected level of ambient light and to selectively control luminance of the displayed image in the second mode based on a second function that relates a level of luminance to a detected level of ambient light in the second mode.