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Technology
Structure and priceple of operatio of fluorescent lamps
1. Basic structure	The basic structure of fluorescent lamps is shown in the figure at the right. Each electrode located at either end of the tube consists of a double or triple coil filament made of tungsten. The coil filament is coated with an electron emission material (emitter) that emits the thermoelectrons, and the tube is filled with the appropriate amount of mercury and argon gas to facilitate the electric discharge. Also, phosphor is coated thinly and evenly on the inner wall of the glass tube.
2. Principle of operation	When the supply voltage is applied, the electric current flows to the electrode and the temperature of the filament increases; the temperature of the electon emission material also increases and stars to emit large volume of thermoelectrons. The thermoelectrons move from the negative electrode to the positive electrode due to the voltage applied between the two electrodes, and the electric current flows through the lamp. When moving in the tube, the electrons collide with mercury atoms. The mercury atoms emit the energy obtained through the collision in the form of ultraviolet rays. The phosphor exposed to the irradiation of the ultraviolet rays absorbs the ultraviolet rays and emits visible rays that determine the brightness of a fluorescent lamp. The color of light emitted from a fluorexcent lamp varies depending on the type of phosphor: white, day white, daylight, etc.
Starting method of fluorescent lamps
Fluorescent lamps can be divided into two types depending on the starting method: the preheat start type and the rapid start type. The majority of ordinary fluorescent lamps are included in these tow types.
1. Preheat start type fluorescent lamps and lighting circuit	In this method, the filament is preheated before electrical discharge. In the glow starter method, when the supply voltage is applied, the electric discharge occurs between the bimetallic electrode and the fixed electrode in the starter. Due to the heat generated by this electric discharge, the bimetal is bent, whereupon it makes contact, then it preheats the electrodes of the fluorescent lamp. The electrodes of the fluorescent lamp are heated enough to emit the thermoelectrons. Then as the temperature of the bimetal drops, it breaks the contact and, at that moment, the strong kick voltage that occurs at the choke coil turns on the fluorescent lamp. In addition to this method, there is a manual method in which the same operations of the glow starter are carried out manually using a pull switch or push button.
2. Rapid start type fluorescent lamps and lighting circuit	A preheat start type fluorescent lamp requires some time before it comes on. But a rapid start type requires almost no time, coming on immediately. When a switch is turned on, the electric current flows between the two filaments and the supply voltage is applied to both ends of the lamp. Thwn the filaments are heated to approx. 800C and start to emit thermoelectrons, the lamp comes on. It takes only one second or so. It should be noted, however, that the rapid start method requires a starting aid adjacent to and along with the lamp. There are two types of starting aids: light equipment tha offers such function and a starting aid that is coated on the lamp itself. Almost all of our fluorescent lamps are coated with this type of aid.
General characteristics of fluorescent lamps
Fluorescent lamps have different brightness, electrical properties and life, depending on the conditions of use. Shown right are the influences exerted by the supply power, ambient temperature, power supply frequency and the number of on/off operations.
1. Lumen maintenance	The brightness (luminous flux) gradually decreases with the lapse of lighting time. The brightness decreases relatively sharply until 500 hours or so have elapsed and then levels off thereafter. The figure below shows an example of FL40SW-B. The power consumption hardly changes even at the end of its life.
2. Influence of voltage	The brightness (luminous flux), electric current and power of a fluorescent lamp change in almost exact proportion to the voltage. Voltages exceeding the upper and lower limits also adversely affect the life span of the lamp. To use the lamp most economically, the voltage should be maintained within +6% of the rated voltage.
3. Influence of changes in ambient temperature	Fluorescent lamps are designed to demonstrate the highest performance when the ambient temperature is between 20-25 C. Higher or lower ambient temperatures influence the brightness and the life. When the ambient temperature drops, the starting voltage becomes higher and it takes longer for the lamp to come on. The lamp comes on normally with rated voltage at temperatures down to 0 C, but if the temperature drops below 0 C, it may take longer.
4. Influence of frequency	In Japan, both 50Hz and 60Hz are used. If a ballast that does not match the supply voltage is used, the electric current and luminous flux would change signficantly, not only adversely affecting the life of the lamp but also causing the callast to fail.
5. Influence of the number of on/off operations	The electron emission material coated on the electrodes is subject to greater wear when the lamp is started than during steady lighting. One on/off operation is equivalent to lighting the lamp for one hour. The life of the fluorescent lamp is influenced by the time duration that the lamp remains turned on. Under ordinary use conditions, it is not necessary to be overly concerned, but it is recommended to avoid turning the lamp on/off too frequently.
6. Flickering of lamp	Fluorescent lamps may flicker if the supply voltage waveform is significantly distorted, if the supply voltage is too low or if the ambient temperature is too low.