Directional display apparatus

A directional display apparatus comprising:

• a display device comprising:
• a transmissive spatial light modulator comprising an array of pixels arranged to modulate light passing therethrough;
• a waveguide having an input end and first and second, opposed guide surfaces for guiding light along the waveguide that extend from the input end across the spatial light modulator;
• and
• an array of light sources at different input positions in a lateral direction across the input end of the waveguide, the waveguide being arranged to direct input light from light sources at the different input positions across the input end as output light through the first guide surface for supply through the spatial light modulator into respective optical windows in output directions distributed in the lateral direction in dependence on the input positions,
• the directional display apparatus further comprising:
• a sensor system arranged to detect the position of an observer relative to the display device;
• and
• a control system arranged to operate the light sources to direct light into one or more viewing windows comprising at least one optical window, in dependence on the detected position of the observer,
• wherein the control system is arranged to change the number of optical windows of the one or more viewing windows on the basis of the output of the sensor system and in response to the speed or acceleration of the observer in the lateral direction from the normal to the display device.