Cree XR-E R2-WC LED emitter Variable from 40~200 lumens (manufacturer rated) Voltage input: 3.6V~8.4V 1100mA digitally regulated LED driver circuitry Bezel diameter: 26.5mm Copper base diameter: 19mm Height including support spring: 36.7mm Height excluding support spring: 28.8mmAluminum textured reflector

To access 0%~100% brightness adjustment mode: Click it on and then within one second, half click it and the light will slowly increase from dim to bright.  During the process, the light will blink twice at 40 lumens, twice more at 90 lumens and then twice again at 200 lumens. When the desired level is reached, switch the light off to save the setting.  

The next time you turn the light on it will be in the selected brightness level that you saved.