The self adjusting Reactive Lighting in the NAO headtorch automatically adjusts the shape of the beam and the brightness to what you are doing, making it easier to see and saving battery life. You can get on with what you are doing better and without the distraction of having to use your hands to make adjustments to the light. For example, if your searching for a path or a marker in the distance the beam is narrow and intense. Look down at your map or guide and instanty the light dims so you're not dazzled and changes to a flood to light the pages evenly. You can effortlessly work between close jobs and distant objects and the NAO continuously adapts beam and brightness. Power is provided by a rechargeable Li-ion battery but in emergency can also take 2 x AAA batteries. The battery is recharged through a USB connector enabling it to be charged easily from a computer or share mains and car chargers with other mobile devices. The NAO is water resistant and has a large control switch which can also be locked in the off position to avoid is accidentally coming on in bags or pockets. In addition to 2 selectable light levels there are 4 programmable profiles. Programming can be done using software free for download off the Petzl website.