Depending on your Fitzpatrick skin type the help that additional UV exposure can provide varies. Generally speaking the higher the skin type (the darker skinned you are naturally) the less UV help is needed. I say "help" because it has been demonstrated that melanotan-1 and melanotan II (the melanotan peptides) cause pigmentation to form in the absence of UV exposure however a small amount of UV exposure enhances the process. So while it is technically possible to develop pigmentation without UV the lower your skin type the more a bit of exposure will help (natural sunlight is the absolute best). Also, the lower your skin type the more important it is to really limit the amount of time of exposure (ie: a few minutes particularly initially). Having to add UV exposure to enhance the process may seem a bit odd to those who are naturally able to develop pigmentation but do know that Fitzpatrick skin type I and IIs either cannot ordinarily develop any pigmentation at all (type I) or having difficulty doing so (type II) so with usage of the peptides these folks develop such an ability or their limited preexisting ability is much enhanced.
Some words of caution to those considering using these drugs: They are unlicensed and unregulated and while clinical trials have been conducted with them (in particular melanotan-1, generic name "
afamelanotide") that have so far not shown any lasting deleterious effects, their ultimate safety over the long term remains relatively little known. Also know that if you have moles it is probably advisable to not use the peptides. The peptides do cause moles to darken including what are essentially latent moles that when darkened will appear to be "new" moles. Folks that already have a decent collection of moles on their skin appear to particularly be vulnerable to this issue. Folks who have had a collection of moles and mole prone skin who've have had success using the peptides have first had their bothersome moles removed (particularly on the face and head).
Know that there is an Australian company that has developed a subcutaneous implant of melanotan-1 (under it's generic name and also now its brand name for
melanotan-1, Scenesse) and is currently conducting human trials of it as a medicine for therapy in UV affected skin indications with a target market release date of 2010/11.
Cheers.