CFL consists of a long glass tube fitted with electrodes. The tube is filled with mercury vapour and gas (argon or xenon). The glass tube's interior is coated with phosphor. When electricity is supplied, electrons are released from the electrodes, which excite the mercury atoms causing them to emit ultraviolet (UV) light. The UV light gets absorbed by the phosphor and reradiates the energy in the form of visible light. Since no heating is involved, a fluorescent lamp requires only about 20 per cent of the electrical energy used by an incandescent bulb to produce the same amount of light. In incandescent bulbs, 90 per cent of the electrical energy supplied goes waste as heat rather than light energy.

Saving grace
If all households in Delhi replace 4 ordinary 60-watt bulbs with 4 CFLs of 15 watt, the annual saving of resources and reduction in pollution load will be as follows:

>> Saving of electricity