How does a CFL bulb work?

Thomas Edison’s incandescent lamps brightened the world for a long time. But, the fact is that only 10 to 12% of electrical energy is converted into visible light by an incandescent lamp and the rest is wasted into heat. That is why CFL light bulbs are replacing incandescent lamps very quickly.

CFL stands for Compact Fluorescent Lamp. They are a lot more energy efficient light bulbs than incandescent lamps. To produce the same amount of visible light, a CFL uses only about one-fifth of the electrical energy that would be needed for an incandescent lamp. Though a CFL has a higher purchase price, it saves a lot of your money because of its efficiency over incandescent lamps. Also, CFL bulbs last relatively longer, about six times than an incandescent lamp. So, what makes a CFL bulb makes more energy efficient? Knowing how a compact fluorescent lamp works is important before answering this question.

Working of a CFL bulb (Compact Fluorescent Lamp)

A CFL light bulb consists two main components – (i) a glass tube coated with a layer of fluorescent material from inside and filled with argon and a small amount of mercury vapor, (ii) an electronic ballast circuit.

compact fluorescent lamp (CFL bulb) uncovered

The glass tube of a CFL is bent (or given a spiral shape) and the both ends are fixed into a base so that the tube is sealed. Electrodes are fixed at each end of the tube. The base contains an electronic ballast circuit. The base also incorporates a connector which allows the bulb to fit in standard bulb sockets. The ballast generates an appropriate electric current which passes through the mixture of argon and mercury vapors inside the tube. When a voltage is applied across the electrodes, the gas inside gets ionized and allows the conduction of current. Electric current passing through the gas mixture excites the gas molecules, which causes the production of ultraviolet radiation. The fluorescent coating is usually of phosphor. When the ultra-violet radiation falls on this phosphor coating, it emits visible light. This is how a Compact Fluorescent Lamp works.

How does a CFL save energy?

Visual light output from any bulb is measured in terms of ‘lumens’. Obviously, the efficiency of a bulb would be the amount of lumens produced per watt of the consumed electricity. A 15 watt CFL bulb produces the same amount of lumens as that produced by a 60 watt incandescent lamp. Thus, a CFL saves almost 75% of the electricity over an incandescent lamp. Incandescent lamps have very less efficiency because of their working principle.  They produce energy by heating a tungsten filament. So, most of the energy is lost in heat. No such heating element is used to produce light in a CFL bulb, thus making it more energy efficient.

What is the function of electronic ballast?

As it is already mentioned above, a ballast circuit provides an appropriate current to light up the CFL bulb. If the ballast circuit is not employed and the fluorescent tube is connected directly across the mains supply, it will draw a large current rapidly and uncontrollably increasing. And, within a second, the CFL bulb would overheat and burn out. A ballast circuit provides regulated and controlled supply to start the CFL bulb. During the initial starting, the ballast provides a high voltage which is necessary for the ionization of the gas. Once the lamp glows, the ballast reduces the voltage quickly to that which is required to keep the bulb glowing.

An ugly truth about CFL

A CFL contains mercury vapors, though in a small amount, which is highly poisonous. So, if you break a CFL bulb you have to be very careful while cleaning and disposing it.

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