English: Pulfrich is based on the phenomenon of the human eye processing images more slowly when there is less light, as when looking through a dark lens. Imagine a camera which starts at position X and moves left to right to position Y as shown by the arrow. If a viewer then watches this segment with a dark lens over the left eye then when the right eye sees the image recorded when the camera is at Y, the left eye will be a few milliseconds behind and will still be seeing the image recorded at X, thus creating the necessary parallax to generate right and left eye views and 3D perception.