Eliminate irritating 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 milli- seconds. It lightens just as quickly when you stop. Shade adjusts from #9 to #12 and sensitivity can be set to suit lighting conditions. This Helmet has a 2.75 clear shade for much easier viewing. Shut off is automatic after 30 minutes at idle. Helmets use two AAA batteries (included) and feature a low battery warning light.