omg.. 
hehe okok i'll try to explain consicely..
'any' amount of light can be measured in EVs (exposure values). and
the values are measures in unit of stops.
no need to worree about a scene how many EVs of light there is,
becos ur camera's metering does that for you.
but in terms of camera settings, 1 stop of light in terms of
shutter speed is like this: if u have a shutter of 1/1000 and u
want one stop MORE of light to go in, u'll need a shutter of 1/500.
if u want 2 stops of light more, u'll need 1/250 (and then 1/125,
1/60, 1/30, 1/15, 1/8, 1/4 etc etc) these are all "one stop"
apart.
OR... u could let more light in by opening up ur aperture.
say u are using f/8, and u want one stop more of light, u will open
up to f/5.6 (the smaller the f number, the bigger the hole, the
more light goes in (at a constant shutter)). if u want another
stop, then u will need to open up to f/4, then to f/2.8.
SO... if u put a cpl (circular polariser) on, and say u lose 2
stops of light, it means:
if WITHOUT the cpl ur camera meters at say 1/250 f8. so WITH the
cpl, ur cam will either meter at 1/60 f/8 OR 1/250 f4 OR 1/125
f/5.6. these three values are all 2 stops brighter than 1/250 f/8,
and u need it becos the cpl darkens the image by two stops.
don't worree about the values, the camera will be able to still
meter correctly, but just u know, u are actually putting "2 stops
worth" of sunshades on the lens. 
btw.. for ur reference, the standard f (aperture) stops are: (from
biggest to smallest)
f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32,
f/44, f/64....
these are considered the standard stops, and are all one stop
apart. for ur cam i think u only need to worry about f/2 - f/11?
around there somewhere.. not to sure about the sony.
of course u're not limited to ONE full stop. u can go in increments
of 1/2 stops and even 1/3 stops.. but aiyah this is getting abit
complicated.. 
