This is a mask filter, to fit over a mask.  It provides the same function as amber color filters we also produce, by cutting out the blue light and enhancing the Fluo effect.  Find out more about Fluo diving on our website HERE.   

Cutting most of the blue light and showing the fluo effect, caution that using a fluo torch/mask filter you can not see non fluo objects, so use of a white light torch is critical.