[ho_co]

Or instead of using a hand-held meter, just bracket.

In light that low, the general rule is to double the exposure time repeatedly, since doubling the time is equivalent to admitting one more stop of light.

But generally when one is in light low enough to go through that procedure, more than one of the bracketed exposures will be fine, just giving different emphases to the subject.

The M8 can only handle down to a certain amount of light anyway, so you may be below that threshold.

And a big help of digital cameras is that instant playback of what you got is available.