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]