I use a 40 watt incandescent bulb in my ferm chamber which is on all the time in the winter. But I also ferment in corny kegs so I'm not concerned about light transmission.
Empire Brewing - Bend, OR
Fermenting: Guv'nor ESB
Kegged: Ominous Black Ale, Molotov IRA, 2011 Below Zero Barleywine, Cream Dream Stout, Amarillo IPA, Apfelwein