In a message dated 96-08-21 17:31:27 EDT, you write: << Part of what makes the meteor leave an "impression" on the film is how long its light is projected on each grain on the film. Along the same lines, the cones in the eye are relying on an "impression" of light to let the brain know that something is there. >> ------- Gary, Cones are for color detection...the real night vision are from the rod cells. George Z.