The Fluorescent Lighting System

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Section 10: Fluorescent Lighting Troubleshooting

When it comes to solving problems with incandescent lamps, essentially it comes down to just three things: the lamp is burned-out, or the lamp glass is broken, or the lamp is not getting any electricity. Because fluorescent lamps have more components and sometimes lamps work in pairs or other groupings, more things can go wrong and things get a bit more complicated.

The following table describes the most common problem symptoms for each class of fluorescent lighting, what the probable causes are, and what corrective action should be taken. The likely causes for each problem appear in order, starting with the most likely and ending with the least likely cause. The most likely causes tend to be the ones that are easiest to fix.

The table is divided into four categories of fluorescent lighting: Pre-Heat-Start fixtures (shown in Orange ), Rapid-Start fixtures ( Green ), Instant-Start fixtures ( Blue ), and Compact Fluorescent lamps ( Yellow ). The type most commonly found in office building fixtures are Rapid Start. Pre-Heat and Rapid Start fixtures, or Compact Fluorescent lamps may all be found in homes. Instant Start fixtures are usually found only in commercial facilities and equipment.

If you don't know the difference between these types, please refer to Section 2 first to help determine which type of system you are going to be working with.

Pre-Heat Fixture Troubleshooting
Problem Possible Cause Action
A Lamp or lamps in a fixture won't light at all. No flickering. No electrical power to the fixture. If all lamps in the fixture refuse to light or blink, make sure that the electrical power for the fixture is turned on. The power to some fixtures is controlled from a wall switch or power cord, but the fixture may also contain a power switch.

Make sure all power control switches are turned on.

Fixture requires manual starting. Some desk lamp and under-cabinet fixture models of preheat fluorescent lighting require human intervention each time they are started. The most common models have a pushbutton that must be pressed for two or three seconds and then released in order for the lamp or lamps to start. Such fixtures do not have starters and usually use lamps 18 inches long or shorter.

If this fixture has starters, check the other causes.

Lamp or starter not properly seated in socket or missing. If the fixture contains a single lamp, make sure the correct starter is locked into its socket, and the lamp is correctly positioned in both lamp holders.

Lamps and starters have been known to vibrate or be bumped so that they no longer make electrical contact.

Starters turn clockwise to lock into their sockets, while lamps have an alignment mark on each end of the lamp (usually a depression in the metal cap) that indicates where the tube should be positioned when installed.

If the fixture has more than one lamp, it is unlikely that all lamps and starters came loose at the same time, so check the other causes.

Wrong Size Starter. Although all replaceable starters come in the same size container, they are rated for use with different lamps. FS-2 starters are for use with 18" and 24" lamps. FS-4 starters are for use with 48" lamps. Starters are marked with exactly what size lamps they are to be used with, so be sure to install the right type.
Lamp or starter worn-out. If the fixture contains a single lamp, try replacing the lamp and the starter.

If the fixture has more than one lamp that isn't working, it is unlikely that all lamps and starters failed at the same time, so check the other causes.

Ballast failed. If the fixture contains a single ballast, try replacing the ballast.

If the fixture has multiple ballast's and none of the lamps work, the problem is almost certainly a lack of electricity or low supply voltage. Use an AC voltmeter to verify that the right electrical voltage is reaching the ballast. Do not measure at the lamp sockets or starter socket. The correct voltage for the ballast should be marked on the ballast.

Wiring problem in fixture This is very unlikely, particularly if the fixture was previously working and then quit.

However, if a fixture was recently installed or repaired and hasn't worked since, you may have a wiring error that is causing the problem. A schematic showing the correct wiring is present on almost all ballast's, so compare the wiring of the fixture to that drawing.

It is also possible that rodents have damaged wiring or that wiring has been crushed or worn within the fixture, causing a short. Look for any places where the wiring has been caught by the metal parts of the fixture and replace any damaged wiring with wire of the same gauge and insulation temperature.

High-temperature electrical tape can be used to cover worn insulation, so long as the wire itself isn't damaged.

The ends of a lamp are lit continuously, but the rest of the lamp is dark. Starter worn-out. If the ends of the lamp are constantly lit with no blinking or flickering, it usually indicates that the starter has gotten stuck in the "start" position. Replace the starter. Note that when this happens, it can greatly reduce the life of the lamp. When the fixture is turned off, if the ends of the lamp appear dark or "smoky" in color, the lamp should be replaced as well.
Wrong Size Starter. Although all replaceable starters come in the same size container, they are rated for use with different lamps. FS-2 starters are for use with 18" and 24" lamps. FS-4 starters are for use with 48" lamps. Starters are marked with exactly what size lamps they are to be used with, so be sure to install the right type.
The lamp keeps trying to start (ends blink on and off repeatedly), but lamp doesn't light or remain completely lit, or goes out for periods of time on its own. Lamp and starter worn-out. Replace both the lamp and starter for that lamp. Although only the lamp may be beyond use, starters also age and it is prudent to replace both at the same time.
Wrong type of lamp. Although many rapid-start lamps are also designed for use in pre-heat fixtures, some cannot be used in pre-heat fixtures. The packaging for the lamp must explicitly state that the lamp may be used in pre-heat fixtures. Note that almost all 34 watt "energy saving" 48" lamps cannot be used in pre-heat fixtures.
Wrong Size Starter. Although all replaceable starters come in the same size container, they are rated for use with different lamps. FS-2 starters are for use with 18" and 24" lamps. FS-4 starters are for use with 48" lamps. Starters are marked with exactly what size lamps they are to be used with, so be sure to install the right type.
Ballast failing. A somewhat rare situation. However, a ballast can fail in such a way that brand new lamps fail to start after only a few hours or days of use. If you replace the lamps and the starters with the sizes stated on the ballast and if the new lamps also quit working or show significant darkening at the ends in just a few days, replace the ballast. You may have to replace the lamps and starters again, but this may be cheaper than replacing the ballast first when the ballast didn't really need replacing.

In addition, when a ballast is malfunctioning and overheats, a safety thermal protector inside the ballast can cause the ballast to abruptly turn off (sometimes with an audible "click" or "ping" sound) and all lamps connected to that ballast will go dark. After several minutes when the ballast has had time to cool-down, the ballast turns back on and the lamps come back on at full brightness and may operate for a period of several minutes before shutting off again. This cycle will repeat endlessly until the problem is corrected, although the cycle may get slightly shorter when the fixture is left on for hours. If you see or hear this condition, replace the ballast and the lamps and the starters that connect to that ballast. Ballast's that are overheating like this are probably also leaking, so watch out for any hot tar that may spill out of an overhead fixture when you are working on it.

(If the lamps flicker and blink on and off several times in just a few minutes or seconds, this is probably just a bad lamp(s) or starter(s), not a bad ballast. Replace all lamps and starters connected to the ballast and see if the problem persists before replacing the ballast. If the ballast is faulty, the problem should reappear in an hour or so.)

Line Voltage low. With an AC voltmeter, measure the electrical voltage coming to the fixture. Do not measure power at the lamp or starter sockets. The ballast probably won't work properly if the line voltage is more than 10% below the operating voltage specified on the label on the ballast.

For example, if a ballast is rated for 120VAC, it probably won't work properly if the line voltage is below 108VAC. Other devices in the typical business or residence would not work well if the voltage was so far off. Being 2% off (117VAC instead of 120VAC) probably won't hurt.

If you find that the line voltage is too low, contact the power company or an electrician to investigate the problem.

When the fixture is turned on, it takes a long time for a lamp to initially come on. Slow Starter or Starter worn-out. As starters wear, they may take more and more time to heat and begin the starting process. Replace the starter. If a new starter still takes a long time (more than two to four seconds) and the lamp doesn't flicker or blink, try a new starter made by a different manufacturer.

If the ends of the lamp are constantly lit with no blinking or flickering, it usually indicates that the starter has gotten stuck in the "start" position. Replace the starter. Note that when this happens, it can greatly reduce the life of the lamp. When the fixture is turned off, if the ends of the lamp appear dark or "smoky" in color, the lamp should be replaced as well.

A lamp is bright near the ends, but only half that bright in the middle portion of the lamp. New Lamp. Some lamps, particularly those with reduced mercury content (known by abbreviations or model names like "ALTO" or "ECO", have a peculiar behavior. During the first hour or two of use of a brand new lamp, the lamp will glow dimly over most of the length of the lamp, become bright at the ends and gradually (over as much as an hour), the bright areas on each end of the lamp will grow until the entire lamp glows brightly.

This behavior may be repeated each time the lamp is turned on for the first 20 to 30 hours of use. After this aging period, this behavior doesn't occur or only takes a minute or so to obtain full brightness across the entire tube.

The only action that could be taken would be to leave brand new lamps on for ten to twenty hours to break them in. Otherwise, ignore this artifact.

Lamp starts but glows dimly, may flicker slightly but constantly, and may exhibit "rings" of bright and dim light that appear to move up and down the length of the lamp. Cold Operating Location Fluorescent lamps do not like cold areas, and standard fluorescent lamps exhibit these symptoms when the lamps are cold. Depending on how cold the ambient air temperature is, operating the lamp may eventually warm the gas inside the lamp to the point that the lamp begins operating at or near its full brightness. The artifacts typically begin when air temperatures around the lamp are below 50F.

If the air temperature is considerably colder and if the surrounding air is circulating, the lamps will never generate enough heat to keep their internal temperatures above 50F, so the lamps will continue to glow dimly and flicker.

The solution here are to use enclosed fixtures that provide insulation from colder air temperatures by trapping a limited amount of air around the lamps. When the lamps are operating, the lamps are insulated from a constant fresh supply of cold air, and gradually the air inside the fixture will heat along with the lamps and the lamps will start to operate normally.

In cases where it is not desired to replace the entire fixture, there are plastic lamp sleeves available. The lamp is inserted into these sleeves and a plastic cap on each end seals the lamp inside the plastic tube, allowing only the electrical contacts of the lamp to protrude. This entire assembly is then placed in the socket in the light fixture. Such sleeves are commonly seen on fluorescent lamps in grocery store freezer units, or in outdoor fluorescent lighting used in commercial locations such as the front porch area of stores.

Fixtures that use the High-Output lamps (HO) are typically found in outdoor signs and other locations where exposure to cold temperatures is expected. These lamps provide most of their brightness down to 10F. They can also be protected to operate at even lower temperatures by using enclosed fixtures or lamp sleeves.

Lamp works but has a gray "patch" away from the ends of the lamp made up of thousands of black spots. Sometimes the area is shaped like a feather. Indicates a section of the lamp that is colder than other sections. Sometimes a place inside a lamp will collect a fine deposit of mercury, which can look like a gray feather inside the lamp. A variety of things can cause marks like this, including a fixture located close to an air vent that blows cold air on that part of the lamp. In most cases, simply rotating the lamp 180 degrees and operating the lamp will cause the mark to gradually dissipate. However, it could eventually reappear again, probably at the same location on the same side of the lamp as before.

"Feathers" cause no harm and do not indicate that a lamp is bad or worn out.

Lamp works but has a light or medium gray or brown ring or rings on the inside of the glass near the ends of the lamp. Normal lamp aging. As the lamp operates, material stripped from the cathodes at end of the lamp impacts the cathode on the other end of the lamp. Some of this material impacts and is embedded into the phospher coating on the end of the lamps, gradually causing the end of the lamps to become partly opaque, developing the smoky or burnt look.

This is a normal part of lamp aging, and should be ignored until the lamp eventually fails to start. This aging should be gradual, as the typical fluorescent lamp has at least 10,000 hours of operating life. When the lamp does finally wear out, the discoloration on the end of the lamps can be as dark as coal.

The only case where this would be considered a problem would be if new lamps develop these marks within the first 100 hours of use and have trouble starting. That may indicate that the starter was not replaced, the wrong size starter was used, or the ballast is faulty or the wrong type.

Rapid-Start Fixture Troubleshooting
Problem Possible Cause Action
A Lamp or lamps in a fixture won't light at all. No flickering. No electrical power to the fixture. If all lamps in the fixture refuse to light or blink, make sure that the electrical power for the fixture is turned on. The power to some fixtures is controlled from a wall switch or power cord, but the fixture may also contain a power switch.

Make sure all power control switches are turned on.

Lamp(s) not properly seated in socket or missing. If the fixture contains a single lamp, make sure that the lamp is correctly positioned in both lamp holders. In fixtures with multiple lamps, all lamps may have to be installed and seated in their sockets for the other lamps to operate.

Lamps have been known to vibrate or be bumped so that they no longer make electrical contact.

Lamps have an alignment mark on each end of the lamp (usually a depression in the metal or plastic end caps) that indicates where the tube should be positioned when installed.

If the fixture has more than one lamp, it is unlikely that all lamps came loose at the same time, so check the other causes.

Lamp(s) worn-out. If the fixture contains one or two single lamps, replace all of the lamps that aren't lighting.

If the fixture has more than two lamps that aren't working, it is unlikely that all lamps failed at the same time, so check the other causes.

Ballast failed. If the fixture contains a single ballast, try replacing the ballast.

If the fixture has multiple ballast's and none of the lamps work, the problem is almost certainly a lack of electricity or low supply voltage. Use an AC voltmeter to verify that the right electrical voltage is reaching the ballast. Do not measure at the lamp sockets. The correct voltage for the ballast should be marked on the ballast.

Wiring problem in fixture This is very unlikely, particularly if the fixture was previously working and then quit.

However, if a fixture was recently installed or repaired and hasn't worked since, you may have a wiring error that is causing the problem. A schematic showing the correct wiring is present on almost all ballast's, so compare the wiring of the fixture to that drawing.

It is also possible that rodents have damaged wiring or that wiring has been crushed or worn within the fixture, causing a short. Look for any places where the wiring has been caught by the metal parts of the fixture and replace any damaged wiring with wire of the same gauge and insulation temperature.

High-temperature electrical tape can be used to cover worn insulation, so long as the wire itself isn't damaged.

The ends of a lamp are lit continuously, or the lamp intermittently blinks, or the lamp starts and after a while goes out, then tries to start again. The lamps may completely turn off for a while, and them come back on. Lamp worn out. Replace all lamps that are not lighting. Rapid-Start fixtures with multiple lamps typically operate the lamps in pairs from the same ballast. In such fixtures, the lamps should be replaced in pairs.
Wrong type of lamp. If a fixture contains an energy-saving 34 watt ballast OR an energy saving device that is installed in addition to the ballast, the fixture cannot use 34 watt or other energy-saving lamps. Use only the lamp types listed on the ballast.
Ballast failing. A somewhat rare situation. However, a ballast can fail in such a way that brand new lamps fail to start after only a few hours or days of use. If you replace the lamps with the size stated on the ballast and if the new lamps also quit working or show significant darkening at the ends in just a few days, replace the ballast. You may have to replace the lamps again, but this may be cheaper than replacing the ballast when it didn't need replacing.

In addition, when a ballast is malfunctioning and overheats, a safety thermal protector inside the ballast can cause the ballast to abruptly turn off (sometimes with an audible "click" or "ping" sound) and all lamps connected to that ballast will go dark. After several minutes when the ballast has had time to cool-down, the ballast turns back on and the lamps come back on at full brightness and may operate for a period of several minutes before shutting off again. This cycle will repeat endlessly until the problem is corrected, although the cycle may get slightly shorter when the fixture is left on for hours. If you see or hear this condition, replace the ballast and the lamps that connect to that ballast. Ballast's that are overheating like this are probably also leaking, so watch out for any hot tar that may spill out of an overhead fixture when you are working on it.

(If the lamps flicker and blink on and off several times in just a few minutes or seconds, this is probably just a bad lamp or lamps. not a bad ballast. Replace all lamps connected to the ballast and see if the problem persists before replacing the ballast. If the ballast is faulty, the problem should reappear in an hour or so.)

Line Voltage low. With an AC voltmeter, measure the electrical voltage coming to the fixture. Do not measure power at the lamp or starter sockets. The ballast probably won't work properly if the line voltage is more than 10% below the operating voltage specified on the label on the ballast.

For example, if a ballast is rated for 120VAC, it probably won't work properly if the line voltage is below 108VAC. Other devices in the typical business or residence would not work well if the voltage was so far off. Being 2% off (117VAC instead of 120VAC) probably won't hurt.

If you find that the line voltage is too low, contact the power company or an electrician to investigate the problem.

A lamp is bright near the ends, but only half that bright in the middle portion of the lamp. New Lamp. Some lamps, particularly those with reduced mercury content (known by abbreviations or model names like "ALTO" or "ECO", have a peculiar behavior. During the first hour or two of use of a brand new lamp, the lamp will glow dimly over most of the length of the lamp, become bright at the ends and gradually (over as much as an hour), the bright areas on each end of the lamp will grow until the entire lamp glows brightly.

This behavior may be repeated each time the lamp is turned on for the first 20 to 30 hours of use. After this aging period, this behavior doesn't occur or only takes a minute or so to obtain full brightness across the entire tube.

The only action that could be taken would be to leave brand new lamps on for ten to twenty hours to break them in. Otherwise, ignore this artifact.

Some lamps in a fixture start but only glow dimly, while other lamps in the same fixture may not light at all or may intermittently flicker but generally remain dark. The lamps that are dim remain so indefinitely, but sometimes the lamps will begin to glow brightly immediately if one of the lamps or the fixture is touched, or if other lamps in the area are also turned on. (Replacing the lamps has been tried and it did not correct the problem.) Lamps are not seated correctly and are not making good contact with socket contacts. On Bi-pin lamps, it is possible for the lamp to be inserted and held by the sockets, but both pins on each end of the lamp are not making electrical contact. It is also possible to have one end of the lamp mis-aligned with the socket so that only one pin on that end of the lamp is in a socket while the other pin is outside.

Verify that both ends of all lamps are correctly inserted into each socket and that the lamp is rotated to the the correct position. This is indicated on the end-cap of the lamp as a ridge or indentation that should align with the slot in the end of the socket.

The lamp or lamps that are not installed in the socket correctly can be any of the lamps, including one of the ones glowing dimly. Check all lamps.

Metal reflectors are not installed or are not electrically connected to the ballast, or the ballast and fixture are not grounded. Rapid Start and some Instant Start fixtures must be connected to an electrical ground in order to start properly. In addition, the metal reflector of the fixture must be correctly installed so that it is within 1/2 inches of the lamps AND is in electrical contact with the ballast. A capacitive field is created between lamp and the metal reflector by the ballast during the starting process, and without this field, the lamps may reach normal operating brightness only by an external influence, such as an increase in capacitance caused by you touching the lamps, or by an increase in light (ionization) in the area coming from other sources.

A fixture that has a power cord is grounded through the ground prong on the power plug. In North America, the round prong is ground. Some older buildings have outlets that do not have grounded outlets (sometimes called two-prong outlets instead of three-prong), and a three-prong cord can be plugged-in only by use of a "cheater" adapter. These "cheaters" do not provide a ground, and this can make a fluorescent fixture malfunction that is connected to them. Have a proper grounded outlet installed for use with the fluorescent fixture.

For fixtures that are wired permanently to the buildings electrical system, a ground wire should have been provided as part of the building wiring. In some older commercial buildings, the metal conduit served as the ground, but newer electrical codes require a ground wire to be installed, even when metal conduit is used. If the fixture is permanently installed and the building wiring lacks a proper ground, have a ground installed for locations that need them.

The most likely cause of a fixture grounding problem that suddenly occurs is in the fixture itself, because fixture designs usually rely on clips, screws or other metal fasteners to force electrical contact between the metal reflector and the ballast. This grounding can be defeated if these parts are missing, or if the fixture or replacement parts have been re-painted in such a way that the metal parts now can't make good electrical contact. Always ensure that all fasteners that came with the fixture are re-installed after servicing. When replacing a ballast, use a piece of sandpaper to scratch the paint off the ballast case at the points where the ballast makes contact with the metal fixture. This will help ensure that the ballast is making good electrical contact with the rest of the fixture.

The ground wire from the ballast (normally green in color) must be connected to the electrical supply ground wire, and in some fixtures, a special terminal is provided on the fixture to tie the ballast and supply ground wires together while also making a solid electrical contact with the fixture. Such grounding points may employ a green-colored screw to distinguish them from screws and other hardware meant to mount the fixture.

Fixture sockets are damaged or broken. In some cases, a socket may become brittle and the bakelite or plastic material of the socket housing breaks, and this may prevent the electrical contacts from making a solid connection, and may prevent the contacts from being able to grab hold of the lamp and keep it from falling. If parts of the socket appear to be missing or are obviously cracked, replace the damaged socket.
Line Voltage low. With an AC voltmeter, measure the electrical voltage coming to the fixture. Do not measure power at the lamp or starter sockets. The ballast probably won't work properly if the line voltage is more than 10% below the operating voltage specified on the label on the ballast.

For example, if a ballast is rated for 120VAC, it probably won't work properly if the line voltage is below 108VAC. Other devices in the typical business or residence would not work well if the voltage was so far off. Being 2% off (117VAC instead of 120VAC) probably won't hurt.

If you find that the line voltage is too low, contact the power company or an electrician to investigate the problem.

Ballast failing. In very rare cases, the portion of the ballast involved in establishing the capacitive field can fail. If a rapid-start fixture persists in having start problems after installing good quality lamps (not those two-for-a-dollar specials), and you have made sure the fixture is grounded properly, replacing the ballast is the remaining option.
Lamp starts but glows dimly, may flicker slightly but constantly, and may exhibit "rings" of bright and dim light that appear to move up and down the length of the lamp. Cold Operating Location Fluorescent lamps do not like cold areas, and standard fluorescent lamps exhibit these symptoms when the lamps are cold. Depending on how cold the ambient air temperature is, operating the lamp may eventually warm the gas inside the lamp to the point that the lamp begins operating at or near its full brightness. The artifacts typically begin when air temperatures around the lamp are below 50F.

If the air temperature is considerably colder and if the surrounding air is circulating, the lamps will never generate enough heat to keep their internal temperatures above 50F, so the lamps will continue to glow dimly and flicker.

The solution here are to use enclosed fixtures that provide insulation from colder air temperatures by trapping a limited amount of air around the lamps. When the lamps are operating, the lamps are insulated from a constant fresh supply of cold air, and gradually the air inside the fixture will heat along with the lamps and the lamps will start to operate normally.

In cases where it is not desired to replace the entire fixture, there are plastic lamp sleeves available. The lamp is inserted into these sleeves and a plastic cap on each end seals the lamp inside the plastic tube, allowing only the electrical contacts of the lamp to protrude. This entire assembly is then placed in the socket in the light fixture. Such sleeves are commonly seen on fluorescent lamps in grocery store freezer units, or in outdoor fluorescent lighting used in commercial locations such as the front porch area of stores.

Fixtures that use the High-Output lamps (HO) are typically found in outdoor signs and other locations where exposure to cold temperatures is expected. These lamps provide most of their brightness down to 10F. They can also be protected to operate at even lower temperatures by using enclosed fixtures or lamp sleeves.

Lamp works but has a gray "patch" away from the ends of the lamp made up of thousands of black spots. Sometimes the area is shaped like a feather. Indicates a section of the lamp that is colder than other sections. Sometimes a place inside a lamp will collect a fine deposit of mercury, which can look like a gray feather inside the lamp. A variety of things can cause marks like this, including a fixture located close to an air vent that blows cold air on that part of the lamp. In most cases, simply rotating the lamp 180 degrees and operating the lamp will cause the mark to gradually dissipate. However, it could eventually reappear again, probably at the same location on the same side of the lamp as before.

"Feathers" cause no harm and do not indicate that a lamp is bad or worn out.

Lamp works but has a light or medium gray or brown ring or rings on the inside of the glass near the ends of the lamp. Normal lamp aging. As the lamp operates, material stripped from the cathodes at end of the lamp impacts the cathode on the other end of the lamp. Some of this material impacts and is embedded into the phospher coating on the end of the lamps, gradually causing the end of the lamps to become partly opaque, developing the smoky or burnt look.

This is a normal part of lamp aging, and should be ignored until the lamp eventually fails to start. This aging should be gradual, as the typical fluorescent lamp has at least 10,000 hours of operating life. When the lamp does finally wear out, the discoloration on the end of the lamps can be as dark as coal.

The only case where this would be considered a problem would be if new lamps develop these marks within the first 100 hours of use and have trouble starting. That may indicate that the starter was not replaced, the wrong size starter was used, the ballast is faulty or the wrong type, or the fixture and ballast are not properly grounded.

Instant-Start Fixture Troubleshooting
Problem Possible Cause Action
A Lamp or lamps in a fixture won't light at all. No flickering. No electrical power to the fixture. If all lamps in the fixture refuse to light or blink, make sure that the electrical power for the fixture is turned on.

Make sure all power control switches are turned on.

Some instant start fixtures utilize "disconnect" sockets. If any lamps are missing or not fully inserted into both lamp sockets, power to part or all of the entire fixture may be disconnected. Check that all lamps are fully seated.

Lamp(s) not properly seated in socket or missing. If the fixture contains a single lamp, make sure that the lamp is correctly positioned in both lamp holders. In fixtures with multiple lamps, all lamps may have to be installed and seated in their sockets for the other lamps to operate.

Lamps have been known to vibrate or be bumped so that they no longer make electrical contact.

Lamps have an alignment mark on each end of the lamp (usually a depression in the metal or plastic end caps) that indicates where the tube should be positioned when installed.

If the fixture has more than one lamp, it is unlikely that all lamps came loose at the same time, so check the other causes.

Lamp(s) worn-out. If the fixture contains one or two single lamps, replace all of the lamps that aren't lighting.

If the fixture has more than two lamps that aren't working, it is unlikely that all lamps failed at the same time, so check the other causes.

Ballast failed. If the fixture contains a single ballast, try replacing the ballast.

If the fixture has multiple ballast's and none of the lamps work, the problem is almost certainly a lack of electricity or low supply voltage. Use an AC voltmeter to verify that the right electrical voltage is reaching the ballast. Do not measure at the lamp sockets. The correct voltage for the ballast should be marked on the ballast.

Wiring problem in fixture This is very unlikely, particularly if the fixture was previously working and then quit.

However, if a fixture was recently installed or repaired and hasn't worked since, you may have a wiring error that is causing the problem. A schematic showing the correct wiring is present on almost all ballast's, so compare the wiring of the fixture to that drawing.

It is also possible that rodents have damaged wiring or that wiring has been crushed or worn within the fixture, causing a short. Look for any places where the wiring has been caught by the metal parts of the fixture and replace any damaged wiring with wire of the same gauge and insulation temperature.

High-temperature electrical tape can be used to cover worn insulation, so long as the wire itself isn't damaged.

The ends of a lamp are lit continuously, or the lamp intermittently blinks, or the lamp starts and after a while goes out, then tries to start again. The lamps may completely turn off for a while, and them come back on. Lamp worn out. Replace all lamps that are not lighting. Rapid-Start fixtures with multiple lamps typically operate the lamps in pairs from the same ballast. In such fixtures, the lamps should be replaced in pairs.
Wrong type of lamp. If a fixture contains an energy-saving 34 watt ballast OR an energy saving device that is installed in addition to the ballast, the fixture cannot use 34 watt or other energy-saving lamps. Use only the lamp types listed on the ballast.
Ballast failing. A somewhat rare situation. However, a ballast can fail in such a way that brand new lamps fail to start after only a few hours or days of use. If you replace the lamps with the size stated on the ballast and if the new lamps also quit working or show significant darkening at the ends in just a few days, replace the ballast. You may have to replace the lamps again, but this may be cheaper than replacing the ballast when it didn't need replacing.

In addition, when a ballast is malfunctioning and overheats, a safety thermal protector inside the ballast can cause the ballast to abruptly turn off (sometimes with an audible "click" or "ping" sound) and all lamps connected to that ballast will go dark. After several minutes when the ballast has had time to cool-down, the ballast turns back on and the lamps come back on at full brightness and may operate for a period of several minutes before shutting off again. This cycle will repeat endlessly until the problem is corrected, although the cycle may get slightly shorter when the fixture is left on for hours. If you see or hear this condition, replace the ballast and the lamps that connect to that ballast. Ballast's that are overheating like this are probably also leaking, so watch out for any hot tar that may spill out of an overhead fixture when you are working on it.

(If the lamps flicker and blink on and off several times in just a few minutes or seconds, this is probably just a bad lamp or lamps. not a bad ballast. Replace all lamps connected to the ballast and see if the problem persists before replacing the ballast. If the ballast is faulty, the problem should reappear in an hour or so.)

Line Voltage low. With an AC voltmeter, measure the electrical voltage coming to the fixture. Do not measure power at the lamp or starter sockets. The ballast probably won't work properly if the line voltage is more than 10% below the operating voltage specified on the label on the ballast.

For example, if a ballast is rated for 120VAC, it probably won't work properly if the line voltage is below 108VAC. Other devices in the typical business or residence would not work well if the voltage was so far off. Being 2% off (117VAC instead of 120VAC) probably won't hurt.

If you find that the line voltage is too low, contact the power company or an electrician to investigate the problem.

A lamp is bright near the ends, but only half that bright in the middle portion of the lamp. New Lamp. Some lamps, particularly those with reduced mercury content (known by abbreviations or model names like "ALTO" or "ECO", have a peculiar behavior. During the first hour or two of use of a brand new lamp, the lamp will glow dimly over most of the length of the lamp, become bright at the ends and gradually (over as much as an hour), the bright areas on each end of the lamp will grow until the entire lamp glows brightly.

This behavior may be repeated each time the lamp is turned on for the first 20 to 30 hours of use. After this aging period, this behavior doesn't occur or only takes a minute or so to obtain full brightness across the entire tube.

The only action that could be taken would be to leave brand new lamps on for ten to twenty hours to break them in. Otherwise, ignore this artifact.

Lamp starts but glows dimly, may flicker slightly but constantly, and may exhibit "rings" of bright and dim light that appear to move up and down the length of the lamp. Cold Operating Location Fluorescent lamps do not like cold areas, and standard fluorescent lamps exhibit these symptoms when the lamps are cold. Depending on how cold the ambient air temperature is, operating the lamp may eventually warm the gas inside the lamp to the point that the lamp begins operating at or near its full brightness. The artifacts typically begin when air temperatures around the lamp are below 50F.

If the air temperature is considerably colder and if the surrounding air is circulating, the lamps will never generate enough heat to keep their internal temperatures above 50F, so the lamps will continue to glow dimly and flicker.

The solution here are to use enclosed fixtures that provide insulation from colder air temperatures by trapping a limited amount of air around the lamps. When the lamps are operating, the lamps are insulated from a constant fresh supply of cold air, and gradually the air inside the fixture will heat along with the lamps and the lamps will start to operate normally.

In cases where it is not desired to replace the entire fixture, there are plastic lamp sleeves available. The lamp is inserted into these sleeves and a plastic cap on each end seals the lamp inside the plastic tube, allowing only the electrical contacts of the lamp to protrude. This entire assembly is then placed in the socket in the light fixture. Such sleeves are commonly seen on fluorescent lamps in grocery store freezer units, or in outdoor fluorescent lighting used in commercial locations such as the front porch area of stores.

Fixtures that use the High-Output lamps (HO) are typically found in outdoor signs and other locations where exposure to cold temperatures is expected. These lamps provide most of their brightness down to 10F. They can also be protected to operate at even lower temperatures by using enclosed fixtures or lamp sleeves.

Lamp works but has a gray "patch" away from the ends of the lamp made up of thousands of black spots. Sometimes the area is shaped like a feather. Indicates a section of the lamp that is colder than other sections. Sometimes a place inside a lamp will collect a fine deposit of mercury, which can look like a gray feather inside the lamp. A variety of things can cause marks like this, including a fixture located close to an air vent that blows cold air on that part of the lamp. In most cases, simply rotating the lamp 180 degrees and operating the lamp will cause the mark to gradually dissipate. However, it could eventually reappear again, probably at the same location on the same side of the lamp as before.

"Feathers" cause no harm and do not indicate that a lamp is bad or worn out.

Lamp works but has a light or medium gray or brown ring or rings on the inside of the glass near the ends of the lamp. Normal lamp aging. As the lamp operates, material stripped from the cathodes at end of the lamp impacts the cathode on the other end of the lamp. Some of this material impacts and is embedded into the phospher coating on the end of the lamps, gradually causing the end of the lamps to become partly opaque, developing the smoky or burnt look.

This is a normal part of lamp aging, and should be ignored until the lamp eventually fails to start. This aging should be gradual, as the typical fluorescent lamp has at least 10,000 hours of operating life. When the lamp does finally wear out, the discoloration on the end of the lamps can be as dark as coal.

The only case where this would be considered a problem would be if new lamps develop these marks within the first 100 hours of use and have trouble starting. That may indicate that the starter was not replaced, the wrong size starter was used, the ballast is faulty or the wrong type, or the fixture and ballast are not properly grounded.

Compact Fluorescent Troubleshooting
Problem Possible Cause Action
The lamp won't light. No electrical power to the socket. Make sure all power control switches are turned on. This can be tested by removing the compact fluorescent lamp and temporarily installing a good incandescent lamp to verify that it lights.
Lamp assembly is burned-out. Replace the lamp assembly.
Lamp cannot make electrical contact in the socket. In some fixture designs such as the recessed models, a compact fluorescent lamp assembly may be too large to screw entirely into the socket through the hole provided in the fixture reflector, so the lamp can't receive electrical power. If the lamp doesn't feel like it is completely in the socket but can't be inserted further into the fixture, some other type of lamp may have to be used in this fixture.

Alternatively, hardware stores sell a lamp socket "extender", a device roughly two inches in length and it consists of a lamp socket and a lamp screw base. This is inserted into the existing socket, then the lamp is inserted into the extender. This gets the lamp assembly further away from the base of the fixture, but it may also make the lamp extend out of the fixture.

Circuit is connected to a dimmer or solid state control. Most compact fluorescent lamps cannot be used with dimmers, and will not function properly or at all when connected to these circuits. Dimmable compact fluorescent lamps are available and this capability is clearly marked.

Also, some photocell and timer controls don't use a relay or electrical contact to turn and off the power. Instead, they use a solid state electronic component - usually a triac - to control the power flow. Unfortunately, triacs don't allow 100% of the electricity to flow through when they are conducting, and this can interfere with the electronics in the compact fluorescent lamp base. If the compact fluorescent lamp works correctly in another socket that is controlled from a wall switch, this could be the problem.

Socket on an Emergency Lighting System Some emergency and exit lighting systems in commercial buildings use Direct Current, and some types of compact fluorescent lamps cannot be used here unless the lamp packaging specifically says the lamps can be used in this situation.
The ends of a lamp tubing are lit continuously (usually right at the base), or the lamp intermittently blinks, or the lamp starts and after a while goes out, then tries to start again. Lamp worn out. Replace the lamp. If the lamp can be replaced, try replacing just the lamp. Otherwise, replace the entire assembly.
Circuit is connected to a dimmer or solid state control. Most compact fluorescent lamps cannot be used with dimmers, and will not function properly or at all when connected to these circuits. Dimmable compact fluorescent lamps are available and this capability is clearly marked.

Also, some photocell and timer controls don't use a relay or electrical contact to turn and off the power. Instead, they use a solid state electronic component - usually a triac - to control the power flow. Unfortunately, triacs don't allow 100% of the electricity to flow through when they are conducting, and this can interfere with the electronics in the compact fluorescent lamp base. If the compact fluorescent lamp works correctly in another socket that is controlled from a wall switch, this could be the problem.

Socket on an Emergency Lighting System Some emergency and exit lighting systems in commercial buildings use Direct Current, and some types of compact fluorescent lamps cannot be used here unless the lamp packaging specifically says the lamps can be used in this situation.
Lamp starts but glows dimly, may flicker slightly but constantly, and may exhibit "rings" of bright and dim light that appear to move up and down the length of the lamp. Cold Operating Location Fluorescent lamps do not like cold areas, and standard fluorescent lamps exhibit these symptoms when the lamps are cold. Depending on how cold the ambient air temperature is, operating the lamp may eventually warm the gas inside the lamp to the point that the lamp begins operating at or near its full brightness. The artifacts typically begin when air temperatures around the lamp are below 50F.

If the air temperature is considerably colder and if the surrounding air is circulating, the lamps will never generate enough heat to keep their internal temperatures above 50F, so the lamps will continue to glow dimly and flicker.

The solution is to use compact fluorescent lamps designed for outdoor or cold locations, or use an enclosed fixture. Note that some compact fluorescent lamps cannot be used in outdoor, in damp locations, or in enclosed fixtures, so check the specifications or use instructions that come with the lamp.

Lamp works but has a gray "patch" away from the ends of the lamp tubing that are made up of thousands of black spots. Sometimes the area is shaped like a feather. Indicates a section of the lamp that is colder than other sections. Sometimes a place inside a lamp will collect a fine deposit of mercury, which can look like a gray feather inside the lamp. A variety of things can cause marks like this, including a fixture located close to an air vent that blows cold air on that part of the lamp. In most cases, simply rotating the lamp 180 degrees and operating the lamp will cause the mark to gradually dissipate. However, it could eventually reappear again, probably at the same location on the same side of the lamp as before.

"Feathers" cause no harm and do not indicate that a lamp is bad or worn out.

Lamp works but has a gray or brown ring or rings on the inside of the glass near the ends of the lamp tubing. Normal lamp aging. As the lamp operates, material stripped from the cathodes at end of the lamp impacts the cathode on the other end of the lamp. Some of this material impacts and is embedded into the phospher coating on the end of the lamps, gradually causing the end of the lamps to become partly opaque, developing the smoky or burnt look.

This is a normal part of lamp aging, and should be ignored until the lamp eventually fails to start. This aging should be gradual, as the typical fluorescent lamp has at least 10,000 hours of operating life. When the lamp does finally wear out, the discoloration on the end of the lamps can be as dark as coal.

The only case where this would be considered a problem would be if new lamps develop these marks within the first 100 hours of use and have trouble starting. This may indicate a low or high voltage power problem in the socket or a faulty lamp assembly.

(Information on printing color tables on color printers can be found here.)



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