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Thread: Dimmed LEDs flicker when adjacent flourescents are turned on

  1. #1

    Dimmed LEDs flicker when adjacent flourescents are turned on

    Several years ago I upgraded the lights over the dining table from incandescent to LED, with a dimmer. This has worked well; no flickering visible at any level.

    Recently I replaced 2 of 5 under cabinets from T12 flourescent to T8 flourescent. I installed new, likely electronic, balasts with the new T8s.

    The undercabinets work fine whether the LEDs are on or off.

    The LEDs work fine when the undercabinets are off. However, when the flourescent undercabinet lights are on, the dimmed LED over the table flickers at all but 100% power.

    I do not know if there is a shared neutral between the two circuits. They are on different breakers. Home was built 15 years ago.

    Would upgrading to a newer dimmer solve the problem?

  2. #2
    Senior Member
    Join Date
    Jun 2013
    Posts
    609
    What dimmer do you have on the chandelier and what LED bulbs?
    Residential Lighting and Shading Specialist for CED Escondido

    mbalay@cedescondido.com

  3. #3
    Cree bulbs; not sure which dimmer but Lutron I believe. Boths circuits are "1-way" - only 1 switch.

  4. #4
    Authorized Lutron Contributor
    Join Date
    Dec 2015
    Posts
    71
    What appears to be happening is that there is neutral interaction between the 2 lighting circuits. If they share a neutral back to the panel, as one is dimmed, it will back feed power up the neutral to the other circuit. This can result in the flickering that you are experiencing. LEDs typically offer a very low resistive load, so they are more susceptible to this type of interaction.
    There are a few ways to combat neutral interaction.

    The most effective is to run a separate neutral for each lighting circuit back to the panel. It may not be the easiest solution, but it is the most effective. Next would be adding an incandescent bulb to the effected circuit. This will often stabilize the circuit and reduce or eliminate the interaction.

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