he lamp end held either too tightly or too loosely, can also cause poor contact at the lamp pins. Measure the voltage at the socket terminals to determine if adequate heater voltage is present.
Sometimes, in high-humidity conditions, RS lamps may start slowly or not at all, even though the cathodes are heated properly. This can result from dirt on the lamps, which makes the silicon coating ineffective. It can also be due to a poor silicon coating. If a new installation experiences random starting under high-humidity conditions, low supply voltage or poor silicon coating on the lamps is generally the cause. If you see the same poor starting in high-humidity conditions on an older installation, the cause is usually an accumulation of dirt on the lamps. In this case, just wash the lamps.
Why is the RS lamp surface condition so important? For the lamp to start within the voltage range of the ballast, it is necessary to excite the gas fill inside the lamp by means of an external voltage; thus the excitation ionizes the gas fill. The capacitance between the lamp and reflector or fixture channel assists this external excitation. Of course, you must bond (connect) the metal fixture to the equipment grounding circuit, and operate the ballast from a grounded electrical system. Any dirt or moisture coating on the lamp can reduce this capacitance.
If you experience random starting of RS lamps, check the fixture for proper grounding. As previously stated, for completely reliable starting in RS circuits, you must have a starting aid, defined as an electrically grounded metal strip at least 1 in. wide extending the full length of the lamp. The lamp should be within half in. of the grounded metal strip for 40W lamps and smaller (three-fourths in. for T8 lamps) and 1 in. for higher output lamps.
The modified RS ballast, a version of the RS ballast, reduces power consumption by a few watts, and operates the lamps similar to the standard RS ballast. The only difference is: You reduce or eliminate filament heating, after the lamps ignite, so the 3V to 4V cathode heating voltage reading will not be measured during normal operation.
Slimline fluorescent systems. We use two types of electromagnetic ballast circuits for two-lamp operation of Slimline lamps. The Lead Lag Slimline circuit has two sections: one called the lead section, consisting of an inductive coil and capacitor in series with the lamp; the other section consists only of an inductive coil. The ballast operates one lamp independently. So if one lamp becomes inoperative, the other will still light. You measure starting voltage between Red and White and Blue and White leads.
A Series Sequence Slimline circuit is smaller and lighter than the lead lag type and operates two lamps in series, with the lamps starting in sequence. Measure starting voltage between Red and White leads. Insert lamp in Red and White position, then read the voltage between Blue and Black. For an F48T12 Slimline lamp, the starting voltage is 385V.
The open circuit voltage of a Slimline ballast is high enough to start a lamp with one lamp filament deactivated. The lamp will flicker and become very black at one end. If you don't replace the lamp, the ballast will overheat and fail. If one lamp of an electromagnetic Slimline ballast is operating and the other is not, the temperature of the coil will rise and possibly fail. This problem does not occur with an electronic Slimline ballast, which operates the lamps in parallel.
HID lamp characteristics. The electric arc of HID lamps is much shorter and has a higher photometric brightness than a fluorescent arc. The lamps are also often higher in wattage ratings, and they may require a specific operating position; base-up, base-down, or base-horizontal. Because the precise size of the arc tube and mixture of materials in the tube differ, each type has its own operating and end-of-life characteristics, which often directly relate to maintenance/ troubleshooting concerns. The family of HID sources includes:
Mercury-vapor lamp (MV). With the lowest efficacy of any of the 