Compact fluorescent lamps (CFLs) are available in different shapes and power ratings. These consist of an electronic ballast circuit and a programmable-logic-controlled tubelight. Most CFL manufacturers offer a guarantee of half a year on their product.
In an unserviceable CFL, the filament has reached the end of its life but there is every possibility that the electronic ballast circuit inside the bottom of the CFL is in working condition. The night lamp circuit described here uses the serviceable electronic circuit fitted in the base of an 11-watt CFL.
For constructing this night lamp, remove the CFL glass tube and replace it with four white LEDs as described below. You should be careful not to break the tube as it contains hazardous materials such as mercury. Carefully open the base of CFL holder using an appropriate tool. You can see the electronic ballast circuit on a circular PCB.
Use the components from the ballast circuit and a series combination of four bright white LEDs as shown in Fig. 1. Remove all other components from the original ballast circuit. As per the requirement of light intensity in your room, you can increase the number of white LEDs up to eight.
As shown in Fig. 1, the full-wave bridge rectifier comprising diodes D1 through D4 converts AC voltage into DC voltage. Snubber capacitor C1 at the input reduces the line input voltage of 230V to a very low-level AC voltage. Series current-limiting resistor R2 and series inductor coil L1 avoid voltage spikes.
Fit the circular PCB in the waste CFL holder and your night lamp is ready for use.