UniqueFire 2002D LED Red Flashlight for Night Hunting, Fresnel Lens Zoomable Predator Red Light Rechargeable with Rapid Dimmer Switch & Bracket, Hog Coyote Red Hunting Light Flashlight - Newegg.com
Coast G36 465 Lumens Alkaline Battery Dual Power LED Handheld Flashlight 30829 - The Home Depot
ULTRAFIRE A100 Tactical LED Flashlight Mini,800 Lumen Hunting Handheld Flashlight Focusable 3 Colors Exchange Glass Lens (Generate RED or Green Light) - Amazon.com
optics - Why does this flashlight lens have this shape? - Physics Stack Exchange