FAQ: Will the ambient room lighting impact the quality of my data?

[Sam]

Generally, standard ambient room lighting is optimal for eye tracking, and will not interfere with the EyeLink system's tracking performance, as the camera operates in the infrared (IR) spectrum. However, lighting can impact your data in two important ways: direct IR interference and changes in pupil size.

1. Direct Infrared Interference
   Strong or pulsating infrared light can interfere with the EyeLink system's ability to capture track the eye. To ensure a clean signal, you should:
   • Avoid direct sunlight: Do not operate the system where sunlight can shine directly on the participant or hardware (or cause reflections).
     
   • Disable other IR devices: Turn off any other infrared emitters in the room.
     
2. Changes in Pupil Size (Pupilometry)
   Ambient lighting directly affects the size of a participant's pupils. If you are measuring pupil size, or simply want to ensure the highest quality gaze data, consistency is key.
   • Maintain Consistent Room Lighting: Keep the room's brightness level the same both within a single recording session and across all sessions for a given study.
     
   • Maintain Consistent Screen Brightness: Ensure the display brightness remains consistent between the calibration/validation phase and the actual stimulus presentation.
     
   • Tracking in low light / dark conditions will increase pupil size, increasing the likelihood of the pupil becoming partially occluded by the eyelid
     

Why is this important? Large, sudden changes in lighting (e.g., turning off the room lights mid-session) can cause significant changes in pupil size. Because the pupil does not dilate and constrict perfectly symmetrically, such changes can cause a shift in the computed gaze location, potentially reducing the accuracy of your data.