I've never shot at night but in the day time I've used one of those small LED lights on a flexi arm (basically a single bulb). Attached to the end of the lens (elastic bands) and then positioned the light so that it illuminates the plane of focus so that as soon as the subject goes bright I know that I'm already pretty much in focus.
This, of course, works best when you're not changing the focus (magnification) of the shot.
For night time you might find it helps when focusing whilst a wrist trap mounted light or head torch or other helps you get your camera in the general area for the shot.
Canon 400D Canon 7D, Sigma 150mm f2.8 macro, Sigma 70mm f2.8 macro, Canon 70-200mm f2.8 IS M2, Canon MPE65mm f2.8 macro, sigma 8-16mm, Sigma 120-300mm f2.8 OS, Tokina 35mm f2.8 macro
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