Being unsure of what particular manufacturer's reflective TFT LCD screen the LaVie MX
uses it's hard to nail down the contrast rating, let alone estimate
it. As an example however, LG | Philips is releasing a 800x600 (246 x
184mm) Transflective screen 2Q 2001 with contrast ratio of 5:1 (reflective), and 30:1 (Transmissive).
Now this isn't a purely reflective adaptation, but in situations where the back light is off, a 5:1 contrast rating
is obviously going to be visible (as reference). On the other
end of the spectrum, a typical backlit Transmissive screen can have a contrast rating on the
order of 100 or 200:1. That's a big difference no matter how
you cut it.
All is not lost however. NEC themselves have just announced a 96mm
reflective-type amorphous silicon thin film transistor (TFT) color liquid
crystal display module with a contrast ratio of 40:1. Viewability of the
PDA-destined display appears better then that of the display on the LaVie MX,
but then again there don't appear to be any wires leading away from the screen
in the image tagging along with the press release ;-)