Remember that the big problem so often addressed with ferrets is not that
they need a lot of light, but that they get too little complete darkness.
About 14 hours of complete darkness (or supplemental melatonin) is often
recommended.  Notice the word COMPLETE because it is important.
 
Ferrets are descended from animals who were active at dawn and dusk
(crepuscular activity) and otherwise were in dark burrows.
 
In darkness the body produces melatonin.  When there is too little
melatonin there tends to be more production of luteinizing hormone which
in turn stimulates any reproductive hormone producing glands including
the adrenal glands and that is thought to be the pathway to adrenal
disease.  That is why simulating Winter light levels is important to
avoid the stimulation.
 
Here are some resources to help (Note that at least one of these is on
multiple pages so use the page advance at top and bottom at FHL when
appropriate.):
 
http://www.miamiferret.org/fhc/melatonin.htm
 
The one below is on two pages
http://www.smartgroups.com/message/viewdiscussion.cfm?
gid=1423922&messageid=6480
 
http://www.smartgroups.com/message/viewdiscussion.cfm?
gid=1423922&messageid=10136
 
http://www.smartgroups.com/message/viewdiscussion.cfm?
gid=1423922&messageid=10084
 
http://www.smartgroups.com/message/viewdiscussion.cfm?
gid=1423922&messageid=9863
 
http://www.smartgroups.com/message/viewdiscussion.cfm?
gid=1423922&messageid=9829
 
http://www.smartgroups.com/message/viewdiscussion.cfm?
gid=1423922&messageid=9814
 
http://www.smartgroups.com/message/viewdiscussion.cfm?
gid=1423922&messageid=9784
 
So, the question is more:  "What are you doing to make sure there won't
be too MUCH light or the lights won't stay on too long?", than it is
anything else.
 
(That melatonin primer is incredibly complete for use by most ferret
people when all the resources listed are read.)
[Posted in FML issue 4614]