Auto Dimming Welding Helmets eliminate bothersome face shield flipping. Now you can see exactly where you are at all times and concentrate on the work. A photocell senses the light from the arc and dims the liquid crystal lens in a blazingly quick 0.025 millseconds. It lightens just as quickly when you stop. The lens adjusts from #9 to #12, and sensitivity can be set to suit lighting conditions. Helmets use two AAA batteries (included) and feature a low battery warning light.