3.4. Physical characteristics of lamps
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Principles of operation
A fluorescent lamp generates light from collisions in a hot gas (&#;plasma&#;) of free accelerated electrons with atoms&#; typically mercury &#; in which electrons are bumped up to higher energy levels and then fall back while emitting at two UV emission lines (254 nm and 185 nm). The thus created UV radiation is then converted into visible light by UV excitation of a fluorescent coating on the glass envelope of the lamp. The chemical composition of this coating is selected to emit in a desired spectrum.
Construction
A fluorescent lamp tube is filled with a gas containing low pressure mercury vapour and noble gases at a total pressure of about 0.3% of the atmospheric pressure. In the most common construction, a pair of filament emitters, one at each end of the tube, is heated by a current and is used to emit electrons which excite the noble gases and the mercury gas by impact ionisation. This ionisation can only take place in intact light bulbs. Therefore, adverse health effects from this ionisation process are not possible. Furthermore, lamps are often equipped with two envelopes, thus dramatically reducing the amount of UV radiation emitted.
Electrical aspects of operation
A special electronic circuitry is needed to start the lamp and maintain currents at adequate levels for constant light emission. Specifically, the circuitry delivers high voltage to start the lamp and regulates the current flow through the tube. A number of different constructions are possible. In the simplest case only a resistor is used, which is relatively energy inefficient. For operation from alternating current (AC) mains voltage, the use of an inductive ballast is common and was known for failure before the end of the lamp lifetime inducing flickering of the lamp. The different circuits developed to start and run fluorescent lamps exhibit different properties, i.e. acoustic noise (hum) emission, lifetime (of the lamp and the ballast), energy efficiency and light intensity flicker. Today mostly improved circuitry is used, most especially with compact fluorescence lamps where the circuitry can not be replaced before the fluorescence lamps. This has reduced the occurrence of technical failures inducing effects as those listed above.
EMF
The part of the electromagnetic spectrum that comprises static fields, and fields up to 300 GHz is what is here referred to as electromagnetic fields (EMF). The literature on which kinds, and which strengths of EMF that are emitted from CFLs is sparse. However, there are several kinds of EMF found in the vicinity of these lamps. Like other devices that are dependent on electricity for their functions, they emit electric and magnetic fields in the low-frequency range (the distribution frequency 50 Hz and possibly also harmonics thereof, e.g. 150 Hz, 250 Hz etc. in Europe). In addition, CFLs, in contrast to the incandescent light bulbs, also emit in the high-frequency range of the EMF (30-60 kHz). These frequencies differ between different types of lamps.
Flicker
All lamps will vary their light intensity at twice the mains (line) frequency, since the power being delivered to the lamp peaks twice per cycle at 100 Hz or 120 Hz. For incandescent lamps this flickering is reduced compared to fluorescence lamps by the heat capacity of the filament. If the modulation of the light intensity is sufficient to be perceived by the human eye, then this is defined as flicker. Modulation at 120 Hz cannot be seen, in most cases not even at 50 Hz (Seitz et al. ). Fluorescent lamps including CFLs that use high-frequency (kHz) electronic ballasts are, therefore, called "flicker free".
However, both incandescent (Chau-Shing and Devaney ) and "flicker free" fluorescent light sources (Khazova and O'Hagan ) produce hardly noticeable residual flicker. Defective lamps or circuitry can in some cases lead to flickering at lower frequencies, either only in part of the lamp or during the start cycle of some minutes.
Light Emission, UV radiation and blue light
There are characteristic differences between spectra emitted by fluorescent lamps and incandescent lamps because of the different principles of operation. Incandescent light bulbs are tuned in their colour temperature by specific coatings of the glass and are often sold either by the attribute &#;warm&#; or &#;cold&#; or more specifically by their colour temperature for professional lighting applications (photographic studios, clothing stores etc.). In the case of fluorescent lamps, the spectral emission depends on the phosphor coating. Thus, fluorescent lamps can be enriched for blue light (wavelengths 400-500 nm) in order to simulate daylight better in comparison to incandescent lamps. Like fluorescent lamps, CFL emit a higher proportion of blue light than incandescent lamps. There are internationally recognized exposure limits for the radiation (200- nm) emitted from lamps and luminaries that are set to protect from photobiological hazards (International Electrotechnical Commission ). These limits also include radiation from CFLs.
The UV content of the emitted spectrum depends on both the phosphor and the glass envelope of the fluorescent lamp. The UV emission of incandescent lamps is limited by the temperature of the filament and the absorption of the glass. Some single-envelope CFLs emit UV-B and traces of UV-C radiation at wavelength of 254 nm, which is not the case for incandescent lamps (Khazova and O´Hagan ). Experimental data show that CFLs produce more UVA irradiance than a tungsten lamp. Furthermore, the amount of UVB irradiance produced from single-envelope CFLs, from the same distance of 20 cm, was about ten times higher than that irradiated by a tungsten lamp (Moseley and Ferguson ).
Fluorescent lights use either an electronic or a magnetic ballast. Nowadays, magnetic ballasts are a rather outdated technology that manufacturers are phasing out, and so they&#;re usually only found on older types of lights.
These rely on the principles of electromagnetism, in that when an electrical current travels through a wire, it naturally generates a magnetic force around itself.
A magnetic ballast (also called a choke) contains a coil of copper wire. The magnetic field produced by the wire traps most of the current so only the right amount gets through to the fluorescent light. That amount can fluctuate depending on the thickness and length of the copper wire. If you sometimes hear your light buzz or see it flicker, it&#;s this changing flow of current that&#;s causing it.
Less advanced in their design than electronic models, some magnetic ballasts can&#;t function without the aid of a starter. This small cylinder-shaped component sits behind the light fixture and is filled with gas which, when heated, enables the light to start. This is called the pre-heat method.
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As it can take several seconds for this process to complete, you may see a delay between the moment you flick the switch and when the fluorescent light begins to glow.
If your light fixture has two or more fluorescent tubes, it&#;ll likely use another different method known as rapid-start. Used in older T12 and some T8 tubes, this method functions without a starter.
One advantage of the rapid-start method is that by providing a low, continuous current rather than a strong surge, it prolongs the life of the fluorescent light and can be better for your overall light output. However, keep in mind that it does use more energy.
Using more sophisticated circuitry and components, electronic ballasts can control the current running through fluorescent lights with greater precision. Compared to their magnetic counterparts, they&#;re smaller, lighter, more efficient and&#;by supplying power at a much higher frequency&#;less likely to cause flickering or buzzing sounds. Overall this makes for a more efficient lighting system.
Some older electronic ballasts employ the rapid-start method described above, while newer and more advanced models use what are known as instant-start and programmed-start.
These control gears were developed so lights could be turned on and operated at their brightest at the first flick of the switch. Rather than pre-heat the electrodes, the electronic ballast uses a high-voltage boost (around 600 volts) to heat and light the filaments and then the mercury gas. Though this makes them energy efficient, it also shortens their life, as the surge of voltage every time they&#;re switched on damages them over time.
For this reason, they&#;re commonly used in spaces where the lights are left on for long periods, such as offices, shops and warehouses.
Designed for areas in which the lights are constantly switched on and off, these devices pre-heat the electrodes with controlled amounts of current before applying a higher voltage to start the light.
They&#;re often a feature of lighting that&#;s activated by motion-detection sensors (for example, toilets in workplaces or public venues) and allows the fluorescent light to last for a long time.
When magnetic ballasts break, it is often blamed on the bulb. Look at for these signs indicating that it&#;s your ballast:
You can find out whether the issue is with the device, starter or the lamp with our guide - Easy Fixes for Slow to Start, Flickering or Faulty Fluorescent Tubes.
In order to ensure that the issue is with the ballast, you will want to test it with a multimeter. A multimeter is designed to measure electric current, voltage and resistance. They are inexpensive and can be found at most electronics shop.
These instructions are for guidance purposes only &#; ensure you reference the manufacturers wiring diagrams. If you are missing the instruction manual, most major manufacturers will have opies on their website.
If the multimeter doesn&#;t move: This means the ballast is dead
If the multimeter needle moves across to the right: The multimeter is still working.
If the ballast is not the problem, you may need to replace your fluorescent tube or other components of your lighting . You can find out how to do this safely with the guide Replacing and Recycling Fluorescent Tubes Safely. If you know what fluorescent tube you need, browse our full range here.
The process for swapping out magnetic ballasts for electronic ballasts is pretty simple and straightforward. This is the direction the lighting industry is headed in, so why not swap them sooner rather than later to optimise your space with better, quieter lighting?
There is a risk of electrocution when changing a ballast so if you&#;re unsure ask an electrician to do the job for you.
Separate starters are only found in older control gear, so if a fixture is less than 15 years old it probably won&#;t have a starter. In newer lamps the process provided by a starter is built in, making the function of a separate starter redundant. If the lamp fixture does have a starter, it will be obvious. You should find a small grey cylinder plugged into the light fitting.
High frequency control gear is a modern single ballast that performs the functions of all the different components in the standard switch start circuit. Lights which are operated with a high frequency ballast do not flicker, but instead light up instantly due to the frequency being much quicker.
Switch start is the control gear that has been used by the industry for years. They are general considered old technology and less manufacturers are creating them. Switch start requires a wire wound magnet choke of ballast. Various parts can be replaced for switch start, rather than the whole unit, which could been seen as an advantage in all types of ballasts.
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