Home Garden

How to Dim CFL With Triac

If you connect a standard compact fluorescent lamp to a dimmer that is designed for incandescent lamps, you risk a significant reduction in the life of the lamp. Conventional dimmers are not compatible with ballasts, the electronic units that control the flow of current to CFLs. Most dimmers use bidirectional electronic switches, or triacs, to switch the current on and off, and adapting a triac dimmer to a CFL ballast requires additional components. Since the late 1990s, triac-dimmable CFLs have emerged and most manufacturers now offer versions that include the enhanced electronics.

Things You'll Need

  • Screwdrivers
  • Neon tester
  • Pliers
Show More


    • 1

      Read the manufacturer’s datasheet for the CFL that you want to dim. If it is not triac-dimmable, you will not be able to dim it using a triac dimmer. Check that the triac dimmer is suitable for the supply voltage in your premises.

    • 2

      Turn off the electrical supply to the lighting circuit at the fuse box or circuit breaker. Check that the lamp socket is dead by inserting the CFL and switching on the light switch. The lamp should not light.

    • 3

      Unscrew the screws securing the light-switch cover plate and remove the plate. Unscrew the screws holding the switch in place and pull the switch gently out of the wall box. Use a neon tester to check that there is no power to the switch, placing the blade of the tester on each metal connection terminal and ensuring that the neon remains unlit.

    • 4

      Disconnect all the circuit wires from the switch. There will be two wires for power, and a third if an earth wire is connected. Loosen the clamping screws on the switch terminals and remove the wires.

    • 5

      Connect the circuit wires to the triac dimmer in accordance with the manufacturer’s installation instructions. Usually, the terminals on the dimmer will be identified by a letter or color-coded. Connect the black wire to the dimmer live terminal and the white wire to the dimmer load terminal. Connect the earth wire, if one is present, to the dimmer earth terminal.

    • 6

      Check that all the connections are tight. Insert the dimmer into the wall box and secure it with the fixing screws. Fit the dimmer-switch cover plate and secure it with the fixing screws.

    • 7

      Restore the electrical supply to the lighting circuit. Turn on the dimmer switch and check for correct operation.