alrite mate im new to lamping but went with mate two or so years ago with greyounds and the filter was used to see their eyes, because if you look into the field and think you see a rabbit then shine without filter and its not a rabbit you will spook the rest of the rabbits because its bright without filter whereas if you shine with red filter and spot their eyes you will know its a rabbit then take filter off and slip dog thinks thats the purpose hope this helps