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Fluorescent lamp base connector (C) Daniel Friedman at InspectApedia.com Fluorescent Light Repairs -
Diagnose & fix flickering, dim, humming or dead fluorescent lights

Steps in diagnosing and repairing a flickering fluorescent light:

When one or more fluorescent light fixtures are humming or flickering or if the light simply won't turn on, the problem may be something as simple as a bad fluorescent bulb.

But there are other causes of flickering lights: some are also trivially easy to repair while others require more expertise and cost. Here we sort out the causes and cures for flickering fluorescent lights, and we give details for wiring connections when replacing the ballast or transformer for the fluorescent light fixture shown.

This article series explains how to diagnose and repair fluorescent lights in buildings.

Watch out:  flickering or dimming lights might indicate a dangerous condition risking a building fire or an electrical shock. If the simple bulb or starter repairs we describe here don't cure the flickering, switch off the bad-acting light fixture, leave it off, and ask for help from a licensed electrician.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Fix Flickering, Buzzing, Humming or "Dead" Fluorescent Lights

Flourescent light fixture on a ceiling is an example of a long-used luminaire type light fixture (C) Daniel Friedman at InspectApedia.comHere we discuss the diagnosis and repair of flickering or humming fluorescent light fixtures. The diagnosis and wiring diagrams shown here are for a 30-W T8-type two-bulb light fixture.

The diagnostic procedures for other fluorescent light fixtures will be the same, though the final wiring details will differ for other models of ballast or transformer.

[Click to enlarge any image]

Separately at ELECTRIC POWER LOSS / FLICKERING LIGHTS- home - we give the causes (and cures) of all types of flickering lights.

Watch out: flickering or dimming lights at a building may be more than an inconvenience. While some causes of flickering lights may be normal and harmless, such as flickering in certain types of light bulbs, many others indicate a dangerous condition, risking fire, shock, injury or worse.

The safest approach is to turn off electrical circuits or components that are causing flickering or dimming or acting strangely in any way.

If you cannot safely access your electrical panel to turn off dangerous circuits or components, leave the building and call your local emergency services.

At FLOOD & DISASTER BUILDING DAMAGE REPAIR PROCEDURES we list emergency numbers for various countries from Australia (000) to the U.K. (112). In Canada or the U.S. call 911. In Mexico call 066.

[Click to enlarge any image]

A fluorescent light fixture may be the only electrical device that is flickering, for any of several reasons we will explain below. Other causes of flickering lights are very dangerous.

Below: our photo shows arc flash burning found inside of a fluorescent light fixture that was dis-assembled for inspection and repair.

After changing to a known-good bulb and trying a new starter I figured that the ballast was probably bad. On opening the fixture for further inspection I found signs of overheating at wiring to the ballast, suggesting that replacing the ballast made sense.

A challenge can be to select the proper replacement ballast or transformer and to make sure that it can support the bulbs that will be used in the fixture.

Arc flash burn inside of a fluorescent light fixture, Two Harbors MN (C) Daniel Friedman at InspectApedia.com

Article Series Contents

Watch out: Changing a fluorescent lamp or bulb and changing the fluorescent lamp starter (if your lamp uses a starter) are easy tasks within the ability of most homeowners or occupants.

Electrical wiring is a different story: if you are not trained and comfortable with proper electrical wiring and repair work, hire someone who is qualified.

Making a mistake can cause a building fire, shock, injury, or death.

How do Fluorescent Light Fixtures Work to Produce Light?

Fluorescent light in use (C) Daniel Friedman at InspectApedia.comA fluorescent lamp is a “gaseous discharge” light source.

Fluorescent light is produced by passing an electric arc between tungsten cathodes in a neon tube filled with a very low pressure mercury vapor (about 0.3 atm) and an inert gas such as argon, neon, or krypton.

The electric current or arc excites the low-pressure mercury vapor which generates radiant energy, primarily in the ultraviolet or UV range.

The inert gases (instead of air that contains oxygen) help prevent oxidation or combustion of the mercury inside the tube.

[Click to enlarge any image]

This radiant energy causes the phosphor coating on the inside of the tube to “fluoresce,” converting the ultraviolet light (invisible to the human eye) into visible light.

By changing the composition of the phosphor coating the manufacturer can change the color temperature of the light emitted by the tube.

Start-up Voltage vs. Operating Voltage

Let's look at just how a fluorescent lamp works in more detail.

Fluorescent lamps have two electrical requirements. Start-up voltage and operating voltage.

To start the lamp, a high voltage surge is needed to establish an arc in the mercury vapor between the lamp filaments at each end of the lamp tube.

Those filaments remain hot as long as the tube is lit or "on". The flow of electrons between the lamp filaments excites the electrons in atoms of mercury inside the tube, causing them to emit radiant energy in the form of UV (ultraviolet) light.

The high start-up voltage, at 400-600 V, is supplied by an electrical transformer or ballast in the light fixture.

Once the lamp is started, the gas offers a decreasing amount of resistance, which means that current must be regulated to match this drop. Once the lamp is operating, voltage drops to a much lower level, usually around 93V for tubes under 30 Watts, or from 100-175 V for tubes at 30 Watts or more.

How the Starter Fires Up the Fluorescent Lamp

How a fluorescent light fixture works (C) InspectApedia.com

Our sketch above illustrates the basics of how a fluorescent lamp works. [Click to enlarge any image]

Line voltage enters the ballast / transformer where it is converted to high voltage to operate the lamp

When the circuit supplying the lamp is switched ON, current passes first through the ballast, then across the filaments at one end of the lamp, following the path of least resistance through the starter switch and on through the filaments at the other end of the lamp.

Current flowing through the starter, itself filled with neon or a similar gas, causes an arc between the two contacts in the starter, essentially closing the circuit across the starter switch to permit a high initial voltage to flow to the lamp filaments causing them to heat up, boiling electrons off of the filament surface, ionizing the gas inside the tube or lamp and causing it to light.

As current continues to flow through the starter, a bimetallic strip in the starter heats, curves to close a metal-to-metal contact, stopping the arc inside the starter (as current now flows through the metal contacts). Stopping the arc inside the starter allows its bimetallic strip to cool, opening the starter circuit.

Because current is now flowing through the ionized gas inside the fluorescent lamp the starter is no longer needed.

Once successfully lit, the fluorescent lamp remains on, operating at a lower voltage, giving off light as the ionized gas excites the phosphorescent coating on the inside of the lamp tube.

When the circuit supplying power to the lamp is switched OFF, current ceases to flow through the fluorescent lamp - it is turned off.

- adapted from FLUORESCENT LIGHT STARTER REPLACEMENT and from Sylvania and other sources cited in detail

at FLUORESCENT LAMP INSTRUCTIONS, PARTS, REPLACEMENTS

Fluorescent lamps operate at a very low gas pressure.

Changing the composition of the phosphor powder inside fluorescent tubes changes the spectrum of light produced.

Mercury is present in the lamp in both the phosphor powder and in the vapor.

Fluorescent lamps are more energy efficient than incandescent light bulbs of an equivalent brightness because more of the energy input is converted to usable light and less is converted to heat.

They also have a longer lamp life since there is no filament to burn out. - sources: adapted from IMERC & Sylvania cited in detail

at FLUORESCENT LIGHT FIXTURE BULB / BALLAST DISPOSAL and

at FLUORESCENT LAMP INSTRUCTIONS, PARTS, REPLACEMENTS respectively.

Recommended spot to keep reading: ELECTRIC POWER LOSS / FLICKERING LIGHTS

 

Fluorescent Lamp, Bulb, Socket, Starter & Ballast / Transformer Sources, Instructions

Old and new transformers for flourescent lamps (C) Daniel Friedman at InspectApedia.com

[Click to enlarge any image]

Flickering Fluorescent Light Fixtures

This topic is discussed in detail at ELECTRIC POWER LOSS / FLICKERING LIGHTS

Diagnose a Bad Fluorescent Light Bulb

At DIAGNOSE a BAD FLUORESCENT LAMP / BULB we list the things to check if the fluorescent light won't turn on or if it flickers or buzzes.

Identify Fluorescent Lamp Types / Bulb Codes

This discussion is now at FLUORESCENT LIGHT BULB CODES & TYPES

Also see BULB & LAMP TYPES GUIDE - topic home, for all types of bulbs or lamps.

Photo Guide to Fluorescent Bulbs by Connector / Base

T2 Fluorescent lamp (C) InspectApedia.com

These photos are now at FLUORESCENT LIGHT BULB PHOTOS

For bulb dimensions see the table at FLUORESCENT LIGHT BULB CODES & TYPES

Replace the Fluorescent Lamp / Bulb in the Fixture

This discussion has moved to REPLACE a FLUORESCENT LAMP / BULB

Replacing a Bad Fluorescent Light Starter

This topic is now found at FLUORESCENT LIGHT STARTER REPLACEMENT

Florescent light starter showing that modern GE brand starters for florescent lights are very fragile and poorly made (C) Daniel Friedman at InspectApedia.com

Replacing & Wiring a Fluorescent Light Ballast or Transformer

This information is now at FLUORESCENT LIGHT TRANSFORMER / BALLAST REPLACEMENT

Types of Fluorescent Light Ballast

Please see FLUORESCENT LIGHT TRANSFORMER / BALLAST TYPES

Types of Fluorescent Lamp Sockets

This material got a promotion to its very own page, now found at FLUORESENT BULB SOCKET TYPES

Replace a Bad Fluorescent Bulb Connector or Base

Please see this page: FLUORESCENT LAMP CONNECTOR / SOCKET REPLACEMENT

Fluorescent Light Ballast & Bulb Disposal Regulations

Please go to FLUORESCENT LIGHT FIXTURE BULB / BALLAST DISPOSAL


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