3. How do fluorescent lamps work?
Fluorescent lamps are
made of a glass tube filled with a low pressure mixture of
gases, specifically mercury
and noble gases like
argon, neon, xenon and krypton. The tubes are coated on the
inside with a fluorescent material, usually a compound
containing phosphorous. When the current is switched on, the
starting mechanisms at each end of the lamp produce
electrons that excite the
gases inside the tube and make them release
ultraviolet radiation. The
ultraviolet radiation hits the fluorescent coating and this
Different chemical coatings are used to produce light of
different colours. For instance, lamps can be designed to
produce light that contains more blue light than conventional
incandescent lamps, and therefore simulate daylight better.
Fluorescent tubes can have either a single or a double glass
envelope, which dramatically reduces the amount of UV radiation
emitted since glass is an effective UV-filter.
Older lamps had starting mechanisms that often failed before
the lamp did, which required frequent replacing of the lamps.
They also had other shortcomings: they made a humming noise,
flickered and were not sufficiently energy-efficient. All these
deficiencies were eliminated in
compact fluorescent lamps
(CFLs) through an improved
design of the starting mechanism.
The ionisation that excites the gases inside
fluorescent lamps is not a
concern to health since it only takes place inside the lamp.
produced can diffuse through the protective glass envelope. The
lamp coating and the glass cover affect the amount and the type
of ultraviolet radiation released but in general,
CFLs can emit more
ultraviolet radiation and a higher proportion of blue light than
incandescent lamps. For instance, someone sitting 20 cm away
from certain CFLs with a single glass envelope can receive ten
times more UVB than if the
lamp was incandescent.
Most electric appliances
generate electric and
magnetic fields of low
electromagnetic fields of
both low and intermediate frequency although the exact range
depends on the type of lamp. Little is known about the strengths
of these fields.
As electricity through the power grid is in the form of
alternating current, the
intensity of the light produced by any lamp connected to it
varies cyclically, depending on the
frequency of the power
grid. If this change in light intensity is perceived by the
human eye, then this is defined as flicker. Flicker is virtually
unnoticeable in incandescent lamps but can be quite pronounced
in fluorescent lamps,
particularly older or defective ones. Modern fluorescent lamps
including CFLs have been
designed to reduce this effect considerably and are therefore
called “flicker free”.