IEEE Power Electronics Magazine Compendium - March 2018 - 53

Human Biological Effects of Light Flicker

it cannot be seen, however, flicker can remain hazardous to
humans [2]. We know this because of experience with fluoFlicker can be defined as a rapid repetitive change in
rescent lighting. When fluorescent lamps are controlled by
brightness [1]. At a minimum, flicker is a distraction.
line-frequency magnetic ballasts, a discharge occurs twice
However, it can also become a hazard to health, provokwith each cycle of the electricity supply. The flicker cannot
ing an increased incidence of headaches [2], [3] and even
usually be seen, but it doubles the average incidence of headepileptic seizures [4]-[6]. The hazard depends on the area
aches in office workers [3], triggers migraines in some indiof retina exposed to the flicker and the way in which the
viduals [7], [8], and impairs the performance of visual tasks
light changes with time (frequency and modulation
[9]. The twofold increase in headache
depth), among other factors. When
incidence is due to a small proportion
flicker occurs at frequencies between
of the population who experience rela3 and 70 Hz with a sufficient peak-toWhen looking directly
tively frequent headaches [3], [10].
peak amplitude, the dangers can be
An increased hazard also occurs in
the most catastrophic: a small perat the taillights, the
fluorescent lamps with low-frequency
centage of the population may suffer
light is not blurry, but
magnetic ballasts as they age. Somean epileptic seizure [4]-[6].
times, the discharge may be brighter
Fortunately, almost all flicker in
when glancing at other
when the ac flows in one direction
lighting occurs at or above a frequency
objects, a trail of lights
more efficiently than in the other,
twice that of the ac input power line:
resulting in brightness variation at the
100 Hz in Europe and 120 Hz in North
appears, known as a
frequency of electricity supply. The
America [2]. So in normal operation,
phantom array.
flicker can then sometimes be seen,
commercial lighting may not increase
and, generally speaking, when flicker
the incidence of photosensitive seican be seen, there is a risk of seizures.
zures. Indeed, flicker cannot usually be
When the lamp is operating normally, however, and the
seen when its frequency is greater than the so-called critical
flicker cannot be seen, there may be little risk of seizures,
flicker fusion frequency (CFF), which is usually between ~60
but the possibility of other neurological consequences, such
and 90 Hz, although the frequency varies with the characteras headaches, remains. There are important lessons to be
istics of the light and the observer. Above the CFF, the light
learned from fluorescent lighting, e.g., the negative health
appears continuous, but this does not mean that it is innocueffects from flicker should be mitigated in all possible life
ous. In fact, the flicker can still be seen under certain circycle operations for any lamp technology.
cumstances, as in the case of the LED taillights. Even when

September 2014

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