But wait! As you get closer you see what looks like a "Do Not" circle on the small sign. You shine the car's headlights toward the small sign. (See picture below.) Oh! camping is NOT permitted here.
red "Do Not" circle is easy
to see during the day because red is highly
visible under bright light. However, after the sun
has set, your eyes begin to adapt to the
darkness. As this
happens the subjective brightness of red decreases
in comparison to other colors. This phenomenon,
called the Purkinje shift, makes it more
difficult to see the red "Do Not" circle, especially
on a brown background, because there is little
The fact that this small
sign is difficult to read in low light conditions
is ironic since those are likely
conditions under which people are looking
for a place to camp.
Foley, H. J. and Matlin, M. W. (2009). Sensation and Perception. Needham Heights, MA: Allyn and Bacon.
Copyright © Michael J. Darnell 1999-2010. All rights reserved.