Works with my simplistic X-Light version too.
I think it would be handy to have the info all together right here.

To activate the 50% power mode.
While looking from the front at the LED, depress and hold the button, and then immediately release it at the first sign of light (like starting it in the Brightness Ramp Up mode).

Switch the regular flashlight modes as usually after that. All of them will work in 50% power mode.

To exit the 50% power mode, just turn off the flashlight. You have to repeat the procedure each time you want to switch into the 50% mode.

To determine the current power mode, wave the light back and forth quickly while watching the LED. The trace of light appears as a solid line in 100% power mode, and as a dotted line - in 50% power mode.