Red light will not degrade night vision the way white light does. It can also be used by hunters to avoid spooking game during the pre-dawn hours, as deer see poorly in the red spectrum. The filter is also useful for close range non-tactical applications such as map reading as it reduces the intensity of light output. The flip up filter window allows instant access to white light. Fits all flashlights and weapon lights with a 1.25" diameter bezel.