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The green way to bright light

We often see posters or TV ads advising us to shift from ordinary tube lights and bulbs to CFL lamps. Let's explore why it makes sense, and why it is good for the environment to do so.

Savings we can measure

Try this experiment in your school lab. With your teacher's help, make an electric circuit with wires, a source of electricity, a socket for holding a light bulb and an ammeter. (An ammeter is a device that measures how much current passes through the circuit.) When you have connected the circuit, plug an incandescent bulb (the kind that uses tungsten filaments) into the socket, switch on the circuit, and record the current in the ammeter.

Now switch off the circuit, and replace the bulb in the socket with a CFL lamp. CFL stands for Compact Fluorescent Lamp, which looks like a small tube light and often comes in a twisted spiral shape (see picture). Switch the circuit on and record the current in the ammeter. Was it lesser than the bulb?

How CFLs work

CFL bulbs are made of two parts. The part that gives light is made of a glass tube filled with mercury vapour and a noble gas. The walls of the tube are coated with a 'phosphor' (not to be confused with phosphorus), usually zinc sulphide and some other metal compounds. The phosphor coating is fluorescent, i.e. something which absorbs UV rays and emits visible, white light.

The second part is called the ballast, which you can identify as the box-like thing at the base of the lamp. The ballast helps stabilize the current so that the lamp gives a constant light.

When you switch a CFL on, the mercury vapour picks up the current, and emits ultraviolet (UV) light. This light lands on the 'phosphor' coating. The coating absorbs the UV rays and gives bright light instead.

How CFLs are good for everyone

CFLs have many advantages. Firstly, unlike filament lamps, they give a softer, diffused light. CFL bulbs can give light for up to 15,000 hours, while tungsten filament bulbs last only up to 1,000 hours. CFLs use up to 33% less electricity than ordinary lamps of the same wattage. (Wattage is a measure of how bright the light will be, but higher the wattage, the more power is consumed). And because they emit less heat than bulbs, they save a little work for the air conditioner too!

In the long run, CFL lamps help save more electricity and thus lower the burden on the environment, for we have to burn less coal and build fewer dams. They are good for your home's budget too.

However, we must use them responsibly. As CFL bulbs contain mercury, they must be disposed off carefully when worn out. Also, frequent switching on and off reduces their lifespan.

CFLs use up to 33% less electricity than ordinary lamps of the same wattage.

Tags :     Everyday Chemistry     compact fluorescent lamp     phosphor     ballast     fluorescence    

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