On 30 Sep 2007 07:05:33 GMT, Margo Schulter
wrote:

Based on a conversation with one experienced observer, I got the idea
that urban light pollution can limit dark adaption. Obviously direct
light trespass can do this at any site (thus star party etiquette!),
but somehow I drew the conclusion that urban skyglow, say magnitude 17
per square arcsecond, could prevent the pupil from reaching the dilation
it might attain at a dark site. Of course, I'd like to correct this
(mis)understanding if it's wrong.

Dark adaptation has nothing to do with pupil dilation; it is a matter of
the chemistry of the retina. Urban light pollution can easily affect
dark adaptation- it is often bright enough under urban skies to allow
for mesopic vision, which means it is bright enough that you will not
become fully dark adapted. But under those conditions, your pupil will
certainly reach the same degree of dilation as it would under the
darkest skies.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com