Where To Buy Fluorescent Light Ballast 
When your fluorescent light flickers or makes a loud and annoying hum, a degrading ballast is the cause. Replacing a ballast is different than replacing a light fixture. However, buying a ballast can be expensive, so consider pricing a brand-new fixture for comparison. You can find a new ballast at a hardware store or home center and install it in about 10 minutes.
where to buy fluorescent light ballast
The ballast takes in electricity and then regulates current to the light bulbs, stabilizing the output of the light. In other words, this is what makes the light stay lit. A fluorescent light has to have a ballast in order to work, without it, the current would increase as it passed through, ruining the lamp all together.
While we are focusing on fluorescent lamps in this article, it's also important to check that the tubes aren't self-ballasted LEDs. "Plug-and-play" LEDs have become a popular option to replace fluorescent tubes when either the tubes need to be replaced or the ballast fails.
Ballast factor determines the light output of the lamps. For example, lamps powered by a .88 ballast factor will produce less light than if they are powered by an equivalent ballast with a factor of 1.2. The ballast factor is primarily a determination of light output, but it also has an impact on energy consumption.
In some cases, you may want a dimmable fluorescent ballast. While this is uncommon, check the specifications to make sure the ballast you are buying is dimmable and also compatible with other products, like the bulbs and dimmer.
I several "cloud"" fluorescent light fixtures in my house. One no longer lights at all. The second is very dim but both lamps are lit, and the third will only light one of the two bulbs. I've changed out the bulbs with new ones, but the problem still exists. The light fixtures are about 7 or 8 years old. I'm thinking the ballasts need to be replaced.
Answered by LCD: I presume you have checked the bulb types match the fixture - there are now three types of bulbs with the same ends that will fit different types of fixtures (T8 and T12 are the commonly available ones - don't remember the other type offhand, which is used in industrial applications) - use the wrong bulb type and they will either burn out prematurely, or fail to light fully. Also, some bulb brands are designed for use in only magnetic ballasts, and some only in electronic - which can also cause your problem. I am guessing offhand you might have this mismatch problem - check label on fixture and ballast, then check bulb manufacturer specs on type of ballasts acceptable for the bulbs you have. This actually sounds like it might be your problem, especially since ballasts typically last 20 or more years.
A replacement ballast costs about $10-25 depending on capacity and brand. The bite is that an electrician trip charge (which includes 30 or 60 minutes work) is going to be $75-150 probably - for about 5 minutes work on each light fixture.
If these are ceiling flush mount fixtures (as opposed to recessed or trougher type), which is what it sounds like your case is, you may well be able to buy new ones and install them yourselves as cheap as buying a replacement ballast - or take this chance to change light fixture if you want - and avoid the electrician charge totally. New fixtures also commonly come with bulbs too - making them respectively cheaper. In fact, for some plain fixtures like 4 foot shop lights, a new fixture with bulbs can be cheaper at a box store than just two bulbs alone.
To see if it is the ballasts - move the currently working bulb around between all the light positions (with power off while changing out) - if it works where a bulb currently does not, then the ballast is almost certainly OK and the problem is bad or wrong type bulbs.
Answered by LCD: To the questioner on pole-mounted 100W ballast replacement - I can't imagine a flourescent light being pole-mounted for parking lot or street lighting, so I am guessing you are talking a HID (High Intensity Discharge) security large-area coverage lamp, because 1000W is awfully high for a parking lot or street light.
So you might ask them if cheaper to replace ballast or to replace the light with a ballast-free light like LED is cheaper. Assuming that and not the light sensor is the problem - sometimes replacing or even just cleaning bird droppings off a photosensor is all it takes to fix it. lso - how do you know it is the ballast. If a light with ignitor capacitor and ballast like high pressure sodium, commonly they start flickering and failing to fully ignite as they reach end of life and it is just the bulb, not the ballast going bad - though let it keep going doing the flickering or continual restart attempt thing and it will take out the ignitor and/or ballast in fairly short order. Or might be the ignitor (capacitor) - but without diagnosing I would not just replace the ballast considering what it costs.
Considering ballast replacement costs (now and every 10-15 years or so maybe) and potentially VERY significant (commonly 2/3 - 3/4) electric savings, changing to a more modern light may save you a LOT of $ in the long run - especially since they (if they meet the claimed life) last the 3-5 times as long as a conventional lamp (though my experience is LED lights typically last 10-15% of claimed life in intermitent on-off type use, maybe 20-30% in overnight use, and only come anywhere near to claimed life in continuous service because the starting electronics fail.
A familiar and widely used example is the inductive ballast used in fluorescent lamps to limit the current through the tube, which would otherwise rise to a destructive level due to the negative differential resistance of the tube's voltage-current characteristic.
Ballasts vary greatly in complexity. They may be as simple as a resistor, inductor, or capacitor (or a combination of these) wired in series with the lamp; or as complex as the electronic ballasts used in compact fluorescent lamps (CFLs) and high-intensity discharge lamps (HID lamps).
An inductor, usually a choke, is very common in line-frequency ballasts to provide the proper starting and operating electrical condition to power a fluorescent lamp or HID lamp. (Because of the use of the inductor, such ballasts are usually called magnetic ballasts.) The inductor has two benefits:
An electronic ballast uses solid state electronic circuitry to provide the proper starting and operating electrical conditions to power discharge lamps. An electronic ballast can be smaller and lighter than a comparably rated magnetic one. An electronic ballast is usually quieter than a magnetic one, which produces a line-frequency hum by vibration of the core laminations.
Electronic ballasts are often based on switched-mode power supply (SMPS) topology, first rectifying the input power and then chopping it at a high frequency. Advanced electronic ballasts may allow dimming via pulse-width modulation or via changing the frequency to a higher value. Ballasts incorporating a microcontroller (digital ballasts) may offer remote control and monitoring via networks such as LonWorks, Digital Addressable Lighting Interface (DALI), DMX512, Digital Serial Interface (DSI) or simple analog control using a 0-10 V DC brightness control signal. Systems with remote control of light level via a wireless mesh network have been introduced.
Because more gas remains ionized in the arc stream, the lamp operates at about 9% higher efficacy above approximately 10 kHz. Lamp efficiency increases sharply at about 10 kHz and continues to improve until approximately 20 kHz. Electronic ballast retrofits to existing street lights had been tested in some Canadian provinces circa 2012; since then LED retrofits have become more common.
Application of electronic ballasts to HID lighting is growing in popularity. Most newer generation electronic ballasts can operate both high pressure sodium (HPS) lamps as well as metal-halide lamps. The ballast initially works as a starter for the arc by its internal ignitor, supplying a high-voltage impulse and, later, it works as a limiter/regulator of the electric flow inside the circuit. Electronic ballasts also run much cooler and are lighter than their magnetic counterparts.
Although an inductive pulse makes it more likely that the lamp will start when the starter switch opens, it is not actually necessary. The ballast in such systems can equally be a resistor. A number of fluorescent lamp fittings used a filament lamp as the ballast in the late 1950s through to the 1960s. Special lamps were manufactured that were rated at 170 volts and 120 watts. The lamp had a thermal starter built into the 4 pin base. The power requirements were much larger than using an inductive ballast (though the consumed current was the same), but the warmer light from the lamp type of ballast was often preferred by users particularly in a domestic environment.
Resistive ballasts were the only type that was usable when the only supply available to power the fluorescent lamp was DC. Such fittings used the thermal type of starter (mostly because they had gone out of use long before the glow starter was invented), but it was possible to include a choke in the circuit whose sole purpose was to provide a pulse on opening of the starter switch to improve starting. DC fittings were complicated by the need to reverse the polarity of the supply to the tube each time it started. Failure to do so vastly shortened the life of the tube.
An instant start ballast does not preheat the electrodes, instead using a relatively high voltage (600 V) to initiate the discharge arc. It is the most energy efficient type, but yields the fewest lamp-start cycles, as material is blasted from the surface of the cold electrodes each time the lamp is turned on. Instant-start ballasts are best suited to applications with long duty cycles, where the lamps are not frequently turned on and off. Although these were mostly used in countries with 100-120 volt mains supplies (for lamps of 40 W or above), they were briefly popular in other countries because the lamp started without the flicker of switch start systems. The popularity was short lived because of the short lamp life. 041b061a72