On Sat, 19 Apr 2014 21:16:30 +0100, John Rumm
wrote:

On 19/04/2014 13:26, Dave Plowman (News) wrote:
In article ,
charles wrote:
So why don't they flicker when the studio is running at 625/50 - since
it's not locked to the mains frequency? The eye would see a flicker at
much lower speeds than 10 a second.

I'm not a physician. Could the brain sense flicker at less than 0.1Hz?

It's one of these things which seem to vary from person to person. Many
complain about flicker from some 50 Hz fluorescent lights saying it gives
them a headache. I can't say I've ever noticed it.

Much depends on the circumstance I find. 50Hz lights don't seem to
bother me particularly, but CRT flicker at anything less than about 82Hz
really bugs me. (as do modern electronic cats eyes, and some brake
lights, and many LED displays etc).

Don't overlook the fact that the flicker rate of a lamp will be twice
the mains frequency so all those 50Hz lights are actually flickering
at 100Hz. Fluorescent lamps can introduce a 50Hz flicker component
when the cathodes start wearing out. AFAICR from my "Lamps and
Lighting", the imbalance only needs to a mere 3% for it to become
observable by most people.

Multiplexed displays (whether gas discharge or LED based) tend to
have very low refresh rates in relation to hiding the effect that's
magnified by the very low duty cycle of each digit which, on an eight
digit display will be less than 12.5% for each of the 8 digits.
digital oven clocks are a prime example of this deficiency.

As for LED rear brake lights and electronic cats eyes, the problem is
also exacerbated by very low duty cycles and them mainly being
observed in the near peripheral vision in very dark conditions.

Wobble of the image on the retina can produce a confusing mess of
'dots' instead of a smear if the refresh frequency is too low.
Provided the refresh rate is high enough, the resulting series of dots
should produce a 'join the dots' type of effect which is a far less
disconcerting facsimile of a smear we'd happily accept with continuous
illumination.

I'd say you're not alone in observing the worst evils of such
illumination.
--
Regards, J B Good