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Older and some low-cost modern fluorescent fixtures solve the starting problem by the use of a "starter". All pre-heat lamps are "bi-pin", in that they have two electrical contacts on each of the lamp. Connected to each pair of contacts is a filament that is located inside each end of the lamp. This filament is similar to the ones found in an incandescent lamp. When the pre-heat fluorescent fixture is first turned on, current flows through both of these filaments, which heats the gas around them.
When a gas is heated, its resistance to conducting electricity goes down. After a few seconds of heating, the electricity stops flowing through the filaments and the fixture attempts to send the electricity through the gas in the fluorescent lamp. If the gas was sufficiently heated, the electricity now conducts (also called "arcing") through the lamp, creating light.
Fluorescent fixtures that have to heat the gas in order to start the lamp are called "pre-heat" fixtures, and all have a mechanism called a "starter". Pre-heat fixtures either have an automatic starter or require a manual starting action.
In fixtures that automatically start, there is a device known as the Starter. The Starter is usually housed in a small cylindrical metal can that can be removed and replaced, while some low-cost "shop" fixtures may have a non-replaceable starter inside the fixture. Compact fluorescent lamps may have the starter in the base with the ballast, or built into the lamp assembly.
The automatic starter works by having a higher electrical resistance than a warm fluorescent lamp, and also having a lower electrical resistance than a cold fluorescent lamp. This means that when the lamp is cold and not conducting at all, the electricity will then flow through the starter, and through the filaments on each end of the lamp, but not through the gas in the lamp. The starter is designed to allow electricity to flow through it for a short period of time (usually less than two seconds) with almost no resistance, then the starter abruptly increases its resistance. When the starter resistance jumps from zero to the higher value, the flow of electricity will seek a lower resistance path, and the path through the lamp should now have a lower resistance than the path through the starter. If the lamp still hasn't warmed-up enough to conduct, the starter will repeat this cycle until it succeeds in making the lamp warm enough to operate. This cycling is what causes "burned-out" fluorescent lights to flicker over and over. In such cases, no matter how much heating is done by the starter, the old lamp has too much resistance and can't start or sustain a current flow.
In some older fixtures, primarily desk lamps, a manual starting process is used where the operator was expected to perform the role of the starter. The "On" button would have to be pressed and held down for a few seconds and then released. In fact, pressing the "On" button operated the heating filaments in the lamp or lamps. When the button was released, current would flow through the lamp gas if the gas was warm enough. In many fixtures of this type, the lamp was always connected to the electrical supply, but unless its gas was heated by the starting process, nothing would happen.
Similarly, the "Off" button frequently just disconnected the electrical power for as long as the button is pressed. The idea was that if you pressed the "Off" button long enough, the gas in the lamp would cool down and would not be able to conduct electricity when you let go of the button and the electrical power was restored. Some fixtures made the "Off" button really turn off and leave the power turned off, but most fixtures did not.
Some single-lamp pre-heat ballasts have no polarity and both wires from the ballast may be the same color.
120 VAC pre-heat ballasts for lamps larger than 20 watts typically have connections to hot, neutral and the lamp, instead of just to hot and the lamp as shown above.
There is no defined color for the wiring between the lamp and the starter. For clarity, the color purple is used in these drawings.
Although current is now flowing through both filaments of the fluorescent lamp, the current flow is too low to illuminate the starter filaments or generate any heat to start the fluorescent lamp, but the current flow is enough to heat the starter bulb gas.
[ STARTER ]
[ ]
[ o/ ]
[ / ]
[ +/ o-+ ]
[ | ~~~ | ]
+---------------<>=[-+)~~~(+-]=<>---------------+
| [ ~~~ ] |
| |
| |
| +---------------------------------------+ |
+<>=|-- --|=<>+
| ) FLUORESCENT LAMP ( |
+<>=|-- --|=<>+
| +---------------------------------------+ |
| |
| |
| |
LINE --NEUTRAL--<>-+ (WHITE) +---------------+ |
aka | | |
MAINS --HOT------<>----BLACK--------| BALLAST |-----BLUE--<>--+
| |
+---------------+
In the diagram, the lines marked with a blue color, the <> symbols, and the ~~ symbols inside the starter or fluorescent lamp are all used to indicate where current is flowing.
[ STARTER ]
[ ]
[ o ]
[ ]
[ +---o-+ ]
[ | | ]
+---------------<>=[-+) (+-]=<>---------------+
| [ ] |
| |
| |
| +---------------------------------------+ |
+<>=|-- --|=<>+
| ) FLUORESCENT LAMP ( |
+<>=|-- --|=<>+
| +---------------------------------------+ |
| |
| |
| |
LINE --NEUTRAL--<>-+ (WHITE) +---------------+ |
aka | | |
MAINS --HOT------<>----BLACK--------| BALLAST |-----BLUE--<>--+
| |
+---------------+
In the diagram, the lines marked with a blue color, the <> symbols, and the ~~ symbols inside the starter or fluorescent lamp are all used to indicate where current is flowing.
The ballast now begins its task of limiting how much current can safely flow through through the fluorescent lamp. Up until now, so little current was drawn that the ballast did not have to do anything.
If the fluorescent lamp isn't sufficiently heated to arc, the electricity will resume arcing through the gas in the starter bulb and the starting process returns to Step 2.
[ STARTER ]
[ ]
[ o/ ]
[ / ]
[ +/ o-+ ]
[ | | ]
+-----------------=[-+) (+-]=-----------------+
| [ ] |
| |
| |
| +---------------------------------------+ |
+--=|-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --|=--+
| ) ~~~~~~~FLUORESCENT LAMP~~~~~~~~ ( |
+<>=|-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --|=<>+
| +---------------------------------------+ |
| |
| |
| |
LINE --NEUTRAL--<>-+ (WHITE) +---------------+ |
aka | | |
MAINS --HOT------<>----BLACK--------| BALLAST |-----BLUE--<>--+
| |
+---------------+
In the diagram, the lines marked with a blue color, the <> symbols, and the ~~ symbols inside the starter or fluorescent lamp are all used to indicate where current is flowing.
|NC (ON/START SWITCH -
o/ NORMALLY OPEN)
PUSH )===/
+-------------------o/ o----------------------+
| NO |
| |
| +---------------------------------------+ |
+---|-- --|---+
| ) FLUORESCENT LAMP ( |
+---|-- --|---+
| +---------------------------------------+ |
| |
(WHITE) | +-----+ (BLACK) |
| |NC | |
LINE --NEUTRAL-----+ o/ | +---------------+ |
aka PUSH )===/ | | | |
MAINS --HOT-----------o/ o +-----| BALLAST |-----BLUE------+
|NO | |
+---------------+
(OFF SWITCH -
NORMALLY CLOSED)
In the manual-start fixture, the operator is required to close the "ON" switch for a few seconds, allowing the filaments in the fluorescent lamp to heat the gas in the lamp. When the button is released, the only route the electrical flow can take is to arc through the gas in the fluorescent lamp. If the gas was sufficiently heated, the electricity will now flow through the fluorescent lamp.
To turn the lamp off, the power supply is interrupted briefly. The lamps resistance goes up rapidly when current is not flowing through the gas, so when the current is applied again, the lamp won't light unless the starting process is repeated.
Section 5: Rapid-Start Fluorescent Fixtures (HTML) [NEXT]
Section 6: Instant Fluorescent Fixtures (HTML)
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