Any light with an adjustable rubber strap or clamp strap should be able to fasten to most head tubes. I can strap both my Light & Motion Urban 500 and Serfas SL-255 to the head tube on my Univega. But they won't fit around the much larger diameter head tube on my Globe Carmel hybrid. I strap the Serfas around the suspension fork tube when I want the light at a lower angle.

But I fasten my lights to the head tube or fork because my handlebars are already so cluttered. I usually have a video camera mount, phone mount and handlebar bag or KlickFix adapter on the bars, so there's no room for the lights.

At least one of my riding buddies straps his standard headlights upside down on his handlebars. Not sure why. Maybe he prefers the slightly lower angle, or prefers to keep the top of the handlebar clear. Wouldn't work on my bikes -- the cables would interfere.

The only drawback to these methods is Light & Motion advises against mounting their Urban and similar lights upside down or sideways. The USB recharging port is sealed with a snug fitting plastic cap, but presumably water could infiltrate. Wednesday was the first time I was caught in a downpour and my L&M light was fine. So were my helmet lights by other makers -- those use less snug fitting soft rubber caps but these protected the USB ports well enough.