gnite, 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 HID sources, most of these lamps in the 100V to 1000W ratings have an average rated life of 24,000 hrs. Because of this relatively long life, coupled with a slow reduction in lumen output, you should replace them well before reaching their average-rated life. Normal end-of-life (EOL) is a nonstart condition or very low light output caused by blackening of the arc tube from electrode deterioration.
Metal-halide lamp (MH). Operating conditions, such as lamp burning position and normal variations in supply voltage or ballast characteristics, can affect lamp color and light output of MH lamps. Normally, at its end-of-life, an MH lamp won't start because the mix of materials in the arc tube changes. Therefore, the ballast can no longer sustain an arc.
High-pressure-sodium lamp (HPS). Normal end of life indication is on/off cycling, since the aging lamp requires a higher voltage for operation than the ballast can supply. This cycling sequence is normal, but not desirable, since the cycling can damage or destroy the starting circuit and/or ballast. Thus, you should check a cycling HPS fixture without delay. Other conditions that cause cycling include: a loose electrical connection, faulty internal electrical connection to the lamp or at an outdoor installation, and severe fixture vibration, causing lamp voltage to rise above operating limits.
Low-pressure-sodium (LPS). This lamp, which features high efficacy but somewhat limited applications because of its monochromatic yellow color, uses a U shaped arc tube and a two-pin bayonet base. During its burning hours, the lamp's wattage increases. For example, at 20,000 hrs, a 180W lamp draws 247W, so any ampere reading will reflect this increase in wattage consumption because of aging. When troubleshooting, look at the lamp, ballast, capacitor, ignitor (if used), socket, and perhaps the entire fixture for indications of excessive heat.
Let's look at each fixture component separately:
Lamp. Any cracks or holes in a lamp's outer jacket usually indicate a defective lamp. The pre