How to Stop Fluorescent Lights from Flickering

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Solving the Problem of Flickering Light Fixtures: How to Stop Those Annoying Flickering Fluorescent Lights, The Main Causes of Flickering Fluorescent Lights and How to Fix Them

Guide to Solving the Problem of Flickering Light Fixtures

Electrical Question: Is it normal for a fluorescent light fixture to constantly flicker during a brief time when in use?

  • T8 Light Fixture and Switch
    One of our offices utilizes a 3 tube 120volt T8 fixture in one of the lavatories. This facility uses an emergency 12/24v battery backup lighting system throughout, this room included. Room lighting is controlled by a single throw switch that also controls the ventilation fan. As a staff use only room, lighting is generally off, requiring a “cold start?, causing constantly flickering during the brief time in use. If left on, they stabilize, brighten normally and no longer flicker.
  • Replaced the Tubes
    So far my electrician has replaced the tubes, bypassed the emergency system, replaced the main ballast and recently disconnected the fan circuit in an attempt to eliminate it as an interference source. Still we have no positive results. We are considering replacement of the fixture at this point, but fear the concern will still be present following.
  • Light Fixture in a Cold Room
    Is this a normal system characteristic until warmed and this particular fixture is simply mis-matched for the application, or are there other factors we are overlooking? I have great confidence in my electrician’s ability to diagnose, but even he is baffled. Although we have not inspected yet, I thought maybe the air conditioning duct work in the attic may be too close to the fixture and super-cooling the ballast/tubes, in which case insulating the duct work may correct the concern.

Should we just install a different type of fixture better suited to this short time use application?
We are both baffled, can you offer some advice?
Thanks in advance for your help!

This electrical wiring question came from: Mark, from Denver, Colorado.

Background-Facility general maintenance & repair technician for a group of physician offices.

NOTE: Mark’s  Electrical Skill Level is Novice, with the ability to do minor service, test circuits, replace tubes and ballasts, switches, receptacles, dimming fluorescent systems. The facility extensively uses 277 volt, as well as 120volt systems. He has no certifications, but he uses a proven licensed electrical subcontractor for tasks beyond my capability.

Dave’s Reply:
Thanks for your electrical wiring question Mark.

How to Stop Flickering Fluorescent Lights

Application: Fluorescent Light Fixture
Skill Level: Beginner to Intermediate – Best if performed by a Licensed Electrical Contractor.
Tools Required: Basic Electricians Pouch Hand Tools, a non-aluminum ladder and Voltage Tester.
Estimated Time: Depends on personal level experience, ability to work with tools and access to the light fixture(s).
Precaution: Identify the light circuit, turn it OFF and  Tag it with a Note before working with the wiring.
Notice: Installing additional fixture wiring should be done according to local and national electrical codes with a permit and be inspected.

The Main Causes of Flickering Fluorescent Lights and How to Fix Them

  • Replacing Lamps Before They Burn Out
    If the lamp has dark circles at the ends and needs to be replaced. If the lamp is allowed to burn out in the socket it may cause the ballast to burn out and then it will need to be replaced as well.

    • Replace the bad lamp right away.
  • Align the Lamp Pins in the Sockets
    Both pins of the lamp are not positioned into the socket properly. This will cause the lamp to burn out prematurely and flicked as well.

    • Make sure to align the pins when installing the lamps.
  • Install the Right Lamps
    The wrong lamp has been installed and does not match the ballast specifications.

    • Install the right  lamp.
  • Grounding the Light Fixture
    The light fixture is not properly grounded.

    • Install a ground wire and bond it to the metal frame of the light fixture.
  • Cold Areas and Flickering Lamps
    The light fixture has the older magnetic ballast which does not perform well in cold areas and will make the lamps flicker until they warm up.

    • Replace the ballast with an electronic ballast that is rated for cold areas and install the specified lamps.

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FAQs Frequently Asked Questions and Comments

3 Responses to “How to Stop Fluorescent Lights from Flickering”
  1. Eric says:

    I have just replaced my two florescent bulbs, being 48″ 34 watts and 1 1/2 inch width. They seem to run fine until about ten minutes, then they begin to flicker really bad.
    Any help is greatly appreciated.
    Thanks Eric

  2. Dave Rongey says:

    Hi Dennis,
    Make sure the pins of the lamps are set all the way up into the sockets. If the lamps are properly installed and they will not light up all the way then the ballast will most likely need to be replaced.
    I hope this helps,

  3. Dennis Baker says:

    I have 15 year old 48 inch fluorescent light fixtures in our walk-in closets. The lights in one closet are very dim and flickering. One of them has a 3 inch dark spot on one end. I replaced both lights and only one will come on very dimly. Also, it’s flashing on one end. Since this fixture has no apparent starters, would this indicate a bad ballast or some other problem?


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