Effect of luminance of head-up displays on recognition of visual objects on roads

The purpose of this study is to investigate the effect of visual obstruction when a head-up display (HUD) is presented in front of a driver's field of view. The use of HUDs is expected to increase due to advances in augmented reality (AR) technology. A conventional HUD is displayed at a relatively low position in relation to the driver's viewpoint and has little effect on their front view. However, while an HUD, such as the AR-HUD, is presented in front of the driver's field of vision and helps them in presenting ADAS information, there is a concern that this display may obscure visual objects on the road from the driver's field of vision. An experiment using a mockup consisting of a HUD and a driver's seat was conducted with 28 participants. A passenger car, motorcycle, and crossing pedestrian were presented as visual objects on a 65-in monitor behind the image of the HUD. Participants were asked questions under different conditions with changes in the HUD luminance and asked to correctly answer questions regarding changes in the inter-vehicle distance and the existence of visual objects on the road. The number of correct answers provided by the participants was recorded. The experimental results revealed that the HUD had an effect under the twilight condition wherein the background luminance was low. Furthermore, analyzing the number of correct answers for each visual target revealed that the HUD had an effect under conditions wherein the size of the visual object was small. It was experimentally derived that the luminance ratio Rluminance = 1.1 was the threshold value that affected the recognition of the visual object in the background when the HUD was presented in front of the driver's field of view. The threshold value of the luminance ratio Rluminance obtained in this study can be considered when deciding how to properly display the HUD in front of the driver's field of view.