M-4GREEN Aviation Chart Magnifier with Green illumination and large 4" Inch 3x lens for nighttime aviation and map & chart reading while preserving night vision. (Lens Available with or without 5x bifocal lens) a replaceable green wavelength hi-intensity bulb to help preserve night vision and to show maximum contrast on aviation charts and their magenta colors. Makes a ideal handheld magnifier for first, sailors, pilots, truck drivers, first responders, military crews, anyone who might need to look at a map, and wishes to preserve their night vision. Made in USA