Ease of Use
The Knog Blinder ARC 640 clicks easily between its four modes of High, Medium, Low, and Flash. It is the simplest and most intuitive to operate of all the lights in this test. However the small light mode switch is not glove-friendly. To turn it on, simply hold down on the switch for a second until it illuminates. Once on, one click is required for each brightness mode. To turn off, hold down the switch for a second again until the light goes out.

Beam Quality
The Knog Blinder ARC 640 projects a sufficient beam for urban riding and general bike commuting after dark. However cyclists who ride after nightfall on rural roads or mountain bike trails will need a stronger light.

Features
The Knog Blinder ARC 640 is waterproof and provides four brightness modes: High, Medium, Low and Flash.

Our tester’s bike commute takes thirty minutes each way. Using the Flash mode only, the Knog Blinder ARC went eight days before it needed to be recharged.

Charging is simple, straightforward and cordless (with the option to charge via a traditional USB). The Knog Blinder ARC 640 has an integrated male USB plug that can be slotted directly into a laptop or wall mounted plug USB port for charging, although a Knog-specific charging cable is provided.

Versatility
The Knog Blinder ARC 640 comes with two sets of integrated silicone mounting straps for 25-30mm bars and 30-35mm bars. The straps attach to the handlebars with a sturdy magnet clasp. Once attached, our tester found that the light stayed firmly in place, even when riding over bumps or along rough bike paths. The metal clasp is removable and designed to be used for both sets of mounting straps.

Changing between two different-sized mounting straps is easy but fiddly and requires an Allen wrench. The wrench is included in the kit but it is very small and is one more thing to keep track of.

A helmet mounting kit is included as well and the light can be used beyond biking as a handheld flashlight.