Flicker Information - Arbiter Systems 928A User Manual

Flicker Information

In a sense, flicker is defined as a fluctuation of the
line voltage. It is a very specific problem related to
human perception and incandescent light bulbs, but
not a general term for voltage variations.
The concept behind placing limits on voltage fluc-
tuations is that they cause lights to flicker, which can
be irritating and may cause discomfort. Voltage fluc-
tuations are caused by loads on the power distribu-
tion system, which are located near lighting equipment
(within the same building or powered by the same dis-
tribution transformer), and have changing power or
current levels.
Based on groups of people tested for irritation from
light fluctuations, most tend to be irritated when the
light fluctuates at around 1000 changes/minute. Ap-
parently above 1800 changes/minute light flicker is no
longer perceived. Fluctuations in the rms voltage of
only 0.25% are sufficient to cause noticeable flicker in
light bulbs.
Some Definitions
Voltage Fluctuation: a series of voltage changes, or
a continuous variation of the rms voltage.
Flicker: Impression of unsteadiness of visual sensa-
tion induced by a light stimulus whose luminance or
spectral distribution fluctuates with time.
Short-Term Flicker Indicator, Pst: The flicker
severity evaluated over a short period (10 minutes);
Pst = 1.0 is the conventional threshold of irritability.
A reasonable goal might be to limit Pst values to less
than 1.0 for 95% of the time.
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