As Russ suggests, you could just squeeze and hold the button until you get to about half power. The undocumented feature to do so is simple. Hold the button until the light is just barely visible and release. Then squeeze again until it ramps up in brightness and blinks, which is its way of telling you it thinks it's at max power. Then you're at 50% duty cycle, aka half power. You can tell by flicking the light in an arc, and noticing that it's only lit for half its travel.

As for the blinking modes, you have to squeeze that button for a long time until it ramps up to full brightness, then progresses to slow, fast, rave, then SOS flashing.

To change to intermittent mode, turn the light on and off rapidly 4 or 5 times. To get back to normal on/off mode, squeeze and hold until it turns itself off.