It's not "require" or what.. try to understand what is exposure. There's lots of articles on the net that can explain it better me
What we have to work with is the relation between ISO, Shutter speed, Aperture.
For night shots.. you want black to look black without the noise and everything sharpest, blingest possible right?
ISO: higher ISO = more noise = detailed lost of noise cancelation. So you want to keep this as low as possible
Aperture: Using a smaller aperture like F8 allows for better sharpness across the frame. Lens are usually sharper corner to corner when stopped down.
Shutter: So if you have small ISO, small aperture... this means you have to use a very very slow shutter speed to get the right exposure. With the use of a tripod, this doesn't matter already.
If handheld, naturally you need a faster shutter speed to avoid camera shake and what not, in this case ISO and Aperture will be reversed to whats above lor (like the f2 and high ISO you mention)
LX5 aperture smallest is f8 IINM. If stop down to f8 not nice oredi. Use about f4 cukup.