about light

because i've changed to dvorak keyboard and pingyin Chinese typing mode. i can just type chinese in extreme slow speed, and a little faster in English.
LED's effeciency is lower then 100 lm/W u can see it in Philip and everlight catalog
the fluorescent light's effecience is about 100 lm/W the 節能標章have meansured them
and LED in low quality may have low CRI(color represention index, may lower then 80) or they don't even measure it
the general light level
office lighting
good article in mobile01
a thesis about light color
Lux ≒ 2.5 ×  2^EV = 2.5 * N^2/t
N: relative aperture (f-number)
t: exposure time in s
if you use N@4.0 Iso@100 then Lux = 40 * 1/t(in sec)
about EV in wiki