A fluorescent lamp or fluorescent tube light is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes phosphor to fluoresce, producing visible light.

It is the most efficient among commonly used lamps, producing the maximum amount of lumens per watt. Hence it is considered the workhorse of lamps.







ADVANTAGES-

·  Efficiency: A fluorescent tube light converts electrical power into useful light more efficiently than an incandescent lamp; It produces more than 90 lumens per watt.

· Spread of light: The elongated tubular shape allows for a lavish spread of very efficient and uniform light.

·  Life: The life of a fluorescent tube light is more than 20,000 hours - almost 15 to 20 times that of an incandescent lamp. Newer generation lamps are offering more than 30,000 hours!

· Cost: The initial cost of Fluorescent tube lights is a little more than that of incandescent lights - Rs 75 for a basic one to Rs 300 for one with high Ra or longer life. However the lower energy costs offsets the higher initial cost of the lamp. The longer life also reduces the lamp replacement costs, providing additional saving especially where labour is costly.

· Variety: These tube lights now come with an impressive array of ballasts and controls that not only enhance their life and performance, but also allow them to be individually addressed and dimmed.

·Light colour: Not too long ago, these tube lights emitted a discomfiting bluish-white light and took about 15 second long series of flickers to get ignited. But now due to the improvement in technology, they are available in higher colour temperatures that give out warm light and with a high Ra of 90. Thus the colours of objects appear almost the same as in natural daylight.


Discomfiting bluish light 

Today, because of all these advantages, the humble fluorescent tube light is used extensively in smartly designed offices, classrooms, halls, swanky malls and even homes.


DISADVANTAGES-

· Colour rendering: Fluorescent tube lights with low Ra have phosphors which emit too little red light. This makes the skin to appear less pink, and hence "unhealthy" compared with incandescent lighting. Colored objects also appear muted.

· UV radiation: The discharge of these lamps is in the Ultraviolet (UV) spectrum. Thus UV radiation is a matter of concern. However, laboratory studies have shown that one is exposed to much less UV radiation even after prolonged exposure to Fluorescent tube lights than when exposed to sunlight. Also nowadays, designers are using linear fluorescent tube lights as indirect light sources. Hence most of the light gets reflected off the ceiling or wall and thus the UV content is negligible.

·  Disposal: Fluorescent tube lights contain mercury that needs to be disposed off carefully, once the life of the lamp is over. Nowadays effort is being made to reduce the mercury content, and the new generation lamps have as little as 5mg, down from the earlier 25mg.


Example of recycled fluorescent tubelights

Even though the fluorescent tube light has some disadvantages, lot of effort is being invested by lighting companies in improving this lamp as it is an ideal energy-efficient light source which is finding use in many places.

FTL's are gas-discharge lamps, wherein electricity is used to produce ultra-violet light which causes phosphor  to fluoresce, producing visible light. Other popular types of gas discharge lamps are Metal Halides and Sodium Vapour Lamps.