The geomagnetic field influences the sensitivity of our eyes.

Experiments involving the orientation of animals, especially birds, have shown that the visual system and geomagnetic field are linked. On the basis of these findings, we have addressed the question of whether there is an influence of the geomagnetic field on light-sensitivity of the visual system in man. Here we report on measurements of the photopic sensitivity of the human visual system for a 0.5s test-stimulus without magnetic field and with the full local field of 48 microT rotated into the line of view. The experiments show that the geomagnetic field increases this sensitivity by 6-7%, depending on the stimulated area. Based on this increase the probable change in perception of the background luminance was calculated by the Weber-law.