23 Nov
2010
23 Nov
'10
6:35 p.m.
Some people
are sensitive to flicker, and most LCD monitors, from what
I understand, are backlit by fluorescent light, which does have a
flicker. In particular, people who are prone to migraine headaches
often find that flickering can induce or worsen headaches.
(Fluorescent lights don't bother me, but rapidly flashing lights as
seen in occasional movies can drive me nuts, and even looking at paint
test patterns on a highway as I drive by can be very bothersome. I
don't get headaches from them, but it is very uncomfortable to look at
these things.)
Of course, the refresh rate of CRT monitors can be an issue too, but
if it's high enough, it might no longer be detectable to a person.
Ever pulled an LCD monitor apart to see what was inside? The backlight is driven from a high-frequency inverter
(tens of KHz),
while a CRC vertical retrace is 80-90 Hz at best.
I've seen this sort of comment before in relation ot th flickr from CFL
bulbs. And I am not sure it's necessarily correct.
Yes, the inverter iotself runs at 10s of kHz. But it gets it supply from
the normal 60Hz mains. I could well beleive that if the smoothing of the
input DC was not adequate, you could get a 60Hz component in the output.
I have certainly seen SMPSUs with mains (or twice mains) frequency ripple
on their outputs, due to input side smoothing problems. Yes, the
regulation loop should take care of it, but it may not always do so. And
I wonder how much regulation there is in the inerter of a cheap CFL, or
indeed the backplight of an LCD monitor.
Alas the only LCD TV service manual I have does not contain PSU
schematics (it's not regarded as field-repairable, the signal PCB is, for
all it contains BGA-packaged devices, go figure...), so I can't check.
-tony