Dr Craniax said:
While we're talking about response times, what's the average response
time for a CRT Monitor?
There's really no good way to answer this question - CRTs and
LCDs are VERY different beasts in this regard. In the LCD, rows
of pixels are written (and the pixels in them turned on or off, or at
least "more on" or "more off") more or less simultaneously, and
then stay in the proper state (again, more or less) until re-written
on the next frame time. The "response time" specs tell you how
quickly the LC material changes to its new state after the video
information is written to the pixels. (Still somewhat of an over-
simplification, but it will have to do.) This means that the LCD is
a pretty stable light source, except for those times of transition when
a pixel is changing state.
On the other hand, a CRT works by scanning an electron beam
over a phosphor screen, lighting up tiny areas of that screen to the
proper intensity and then moving on. (These "tiny areas" are NOT
exactly "pixels," but at least for this comparison if it help you to think
of pixels being written, be my guest. We can correct that mis-
understanding later if need be...
) When struck by the beam,
the phosphor lights essentially "instantly" - and then the question is
how long it will keep emitting light after the beam has moved on.
This is described in a phosphor specification known as "persistence,"
and it is surprisingly short for standard color CRT phosphors. For
these, the phosphor is down to less than 10% of its original light output
just a few hundred microseconds (at most! - and the persistence is
NOT the same across all three colors) after the beam is removed
from a given area. You would think that this would result in a horrible-
looking display, but the phosphor actually emits a LOT of light in that
short time, and then the eye integrates those high-amplitude pulses of
light between frames to give the illusion of a stable image. (If you
don't make the pulses often enough, though, the eye can and will pick
up on the fact that this isn't really a stable light source - which is where
"flicker" comes from.)
The bottom line is that LCD "response time" and CRT "persistence"
values are in no way comparable, and the two technologies will
always have a different "look" just due to the fact that one IS
providing a fairly constant, steady light output during the frame times
and the other most definitely is not. This shows up most clearly in
comparing the appearance of motion video on the two. To help the
situation, many LCD displays are starting to insert "black time" (i.e.,
set the whole screen to black) in between the video frames, to give
a more pleasing or "CRT-like" appearance - and this, or various
other methods, would still be needed to provide this appearance
even if the LCD could provide a truly zero response time!
Bob M.
