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 produces light.
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. However, some ultraviolet radiation 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 frequency. CFLs emit 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”. More...