Fluorescent lamps are gas discharge lamps(GDT). In these lamps, electrons are generated by emission. With an ignition voltage, the mercury plasma in the glass bulb is ionized and thus becomes electrically conductive. When mercury atoms located in the glass bulb collide, they emit energy as UV light.
The visible light is produced by the UV radiation, which stimulates the luminescent layer on the inside of the glass bulb to emit light. Ionization is maintained by the electric current supplied through two electrodes. It causes a negative internal resistance, which would cause the current to increase disproportionately with increasing voltage and destroy the fluorescent lamp. For this reason, fluorescent lamps are preceded by a ballast, which essentially consists of a choke that provides current limitation.
The process can also work with cold cathode fluorescent lamps( CCFL). To distinguish between hot and cold cathodes, lamps with hot cathode technology are called fluorescent lamps, while those with cold cathodes are called fluorescent tubes. In compact form, fluorescent lamps are energy-saving lamps.
The color temperature of fluorescent tubes is determined by the phosphors and their composition. Their color rendering index(Ra) reaches values from 80 to as high as 98. As far as color temperatures are concerned, there are versions for daylight with color temperatures between 5,600 Kelvin (K) and 7,000 K, for cool white with 4,000 K, and for warm white with 3,000 K. The color rendering index (Ra) of fluorescent lamps ranges from 0.5 to 0.5. Both the color rendering index and the color temperature are listed in the typing as a numerical code. The digit code has three digits; the first digit is for the color rendering index. A 7 stands for a color rendering index between 70 % and 80 %, an 8 for 80 % to 90 % and the 9 for values above 90 %. The following two digits are the first digits of the 4-digit color temperature.
Fluorescent lamps have a pin base as the lamp cap and achieve a luminous efficacy of 100 lm/W. In addition, they have a much higher efficiency than incandescent lamps and their service life is many times longer.