Measurement of pupil diameter during night driving

The pupil is the significant variable for adaptation to different lighting conditions. Changing its size, the pupil regulates how much light enters the eye and thus the retina. In dim light, the pupil expands to allow more light through. Therefore it plays an important role in critical situations like detecting obstacles or adapting to glare during night-time driving. To analyze the behavior of the adaptation to light intensity situations during night-time driving in a non-invasive way, an eye-tracker has been developed and implemented based on a stereoscopic camera system with an infrared LED lighting to perform robust measuring under varying illumination. This system measures the pupil diameter in real time with a temporal resolution of 60 fps and a measurement uncertainty smaller than 50 μm. A special box was set up to measure pupil size stimulated by quasi-monochromatic light. The luminance level is corresponding to the night-time driving conditions. The first results show that pupil size depends on spectral power distribution of light.