Purkinje effect: At low intensity, blue is more visible than red.

Purkinje effect: At low intensity, blue is more visible than red. A slide with both blue and red filters is inserted into a lantern projector. The purkinje effect reveals that the human eye is more sensitive, at low light levels, to blue light than it is to red. At full intensity, both color spots are easily visible on the screen. As the instructor closes down the iris diaphragm, a point is found where the red spot is no longer visible. At this point, the blue spot, though dim, is still easily seen.