If it is a meter or more thick, however,blue light often can be seen.
VOA: special.2010.01.05
What finally relegated your correspondent's Leica to the top shelf wasn't having to carry a separate light-meter all the time, but a pair of scissors as well.
That might be about to change, though, as South Korea's state-owned Korea Electronics Technology Institute has announced a new image sensor chip that promises to take "vibrant photos" in extreme low-light conditions -- all the way down to 1 lux, which is the equivalent light output of a candle shining one meter away.