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Light Guide: Fluorescent Ballasts

Here's some basic information, if you'd like to know something more specific, please let us know

Types

According to the California Energy Commission, electronic ballasts and magnetic ballasts are the two main types on the market. Adaptable ballasts are a specific type of electronic ballast.

Function

The Lighting Research Center claims that the basic function of any type of ballast is to regulate a lightbulb's input energy and provide starting voltages. A single adaptable ballast can be employed to operate several lamps of varying voltages.

Features

Magnetic ballasts can be bothersome to some people because they flicker upwards of 120 times per second. Electronic ballasts operate relatively quietly, nearly eliminate flicker and are more energy-efficient than magnetic ballasts.

Lightbulbs

Several types of lightbulbs, like high-intensity discharge (HID) lightbulbs including metal halide and high-pressure sodium lightbulbs, utilize ballasts to control energy input. Fluorescent lightbulbs also employ ballasts.

Applications

Electronic ballasts have wider applications and are often used to replace magnetic ballasts. However, high-output light bubs still require magnetic ballasts.

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Thank you Mizuti for your valuable input.I have heard about lighting ballast categories like T5 ,T8 etc. For direct lighting and other they varies it seems. I would like to know the classification and how they differ from each other.Also for calculating lighting level ballast is a factor for office spaces. Then how type of ballast selected for specified lux. calculation to find out lux level and influence of ballast factor in it

Here ya go, chief. If you want to see physical examples of each, you should mosey on over to GlobalSpec (shameless plug) and see some of the products per ballast lamp specification (you can sort by classification!). Here's the direct link to Ballastic missiles lights.

Classification

The letter T is used in front of the number to show the fluorescent bulb is a tube type. Following the letter is a number representing the diameter of the bulb measured in fractions of an inch. Fluorescent bulb widths are measured in eighths of an inch. For example, a T5 bulb is five-eighths of an inch wide, a T8 bulb is 1 inch wide (eight-eighths) and a T12 is 1-1/2 inches (12/8ths) in diameter.

T12 Type

Since its invention in the 1930s, fluorescent T12 bulbs were the choice of building contractors. The low cost and life span of 20,000 hours far surpassed incandescent bulbs. However, because of its less efficient magnetic ballast and larger inefficient bulb size, it has lost popularity to the T8 electronic ballast type. T12 and T8 bulbs are available in the same lengths, however, ordinary T12 bulbs do not operate properly with an electronic ballast and vice versa. According to the National Lighting Board (NLB), a ban effective July 1, 2010, phases out magnetic ballasts, although excess inventory and T12 bulbs will continue to be sold.

T8 Type

Fluorescent T8 bulbs have continued growing in popularity since their introduction to the United States in 1981 and have now become the standard in building construction. The T8 bulb's lifetime meets or exceeds that of the T12, while using less energy. Additionally, the T8 uses an electronic ballast that is more energy efficient than the T12 magnetic type. With the T8 ballast using solid-state circuitry to operate, it does not make a loud humming sound or cause light flickering commonly found with the T12 magnetic ballast.

T5 Type

The T5 fluorescent bulb, like the T8, uses an electronic ballast. That is where the similarity ends. The cost of T5 bulbs, especially high output types, is significantly higher than T8 and T12 bulbs. T5 bulbs are also shorter and do not fit standard fixtures. For example, a typical T5 bulb is 46 inches long rather than the 48 inches (4 foot) of T8 and T12 bulbs. Conversion kits are available, with a ballast, allowing T5 bulbs to fit T8 and T12 fixtures. T5 bulbs save money over time because of a longer lifespan while producing more light with less wattage. The T5 also maintains maximum light output for almost the entire lifetime of the bulb.

Future Technology

T5, T8 and T12 LED (light emitting diode) replacement tubes currently on the market fit into existing fluorescent fixtures. The technology of LEDs is different from fluorescent bulbs with advantages and disadvantages. The biggest factor is price, easily costing ten times more. The advantages are they last up to 50,000 hours, use less power, operate without a ballast and do not contain hazardous mercury that fluorescent bulbs use. Like any new product, cost reduction will depend on improved technology and consumer demand.

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Here is a little more info! Btw, "T" stands for tubular and "C" stands for circular as in those hola-hoop or doughnut shaped lamps. "CF" stands for compact fluorescent.

Just so you know, some of those new electronic ballasts still make noise. It comes from the transformer connected to the 60Hz (or 50Hz) and is caused by a poorly manufacturered stepdown (or stepup) transformer. Typical starting voltages range from an open circuit voltage of 300 VAC to 800 VAC. At one time, some of the electronic ballasts would operate at the same frequency as your TV remote control which would cause all kinds of interesting problems, like changing channels, turning on and off, etc.

The average human retina is only capable of registering a frequency of 30Hz at a 50% duty cycle. Consequently the 120 flashes per second is not the cause of problems with magnetic ballasts. The hum from the transformer-like construction has usually been the primary problem. And the blinking that you could sometimes see when you did register some flashing was more likely a problem with the lamp. Fluorescent lamps make great rectifiers when you loose a coil. Operates just like an old tube circuit. Not good on the ballast, because it becomes saturated the core in one direction and reigniting the arc becomes increasingly difficult over time.

The statement that T5 saves money may be an illusion. My mother-in-law was saving money at one time by replacing all of her 60W and 100W incandescent with 40W bulbs. Sure she was using less wattage, but it was very dark all the time. My point is that you can't look at the wattage only. It is nearly meaningless by itself. You must take into account that measure of light on the box with the term of lumens or in some cases candella. It is a little more complicated than it seems.

Lastly, the phase out of T12 lamps was generally welcomed by the manufacturers because their production machines of the 1950's and 1960's were originally designed to make about 1000 lamps per hour. Over the years, they drove the cost out by cranking up the speed. At the time they were taken out of service, they were throwing around about 5500 lamps per hour. The transfers between stations were the biggest problem. While they kept the cost down by increasing the output per hour, the machines simply hit a point at which they simply could not go any faster. So, the game was over. With T8 and again with T5 the same game was played with larger machines that were designed to run at 6000 per hour. They are now trying how to get 7000 per hour out of them. The line speed is frightening up close. And you can't usually stop the line without emptying everything on it first.

Oh, and I agree, LED's rule! Even some of those use the T1-3/4 term to indicate that it is of a tubular design and it is 0.125*1.75 inches wide. Some things just never die completely...

How much will be the a)PF,b)harmonics,c)EMC etc of EM/electronic/digital ballasts?.

I do not have all the answers, but I would follow THIS link to find the answers.

Friend,

In a fluorescent or HID type lamp, when the input voltage is high enough, the gases inside the tube will allow an arc to occur between the electrodes. Within a few milliseconds, this arc then supplies a large amount of metal ions so the resistance between the electrodes drops quickly and the current flow increases. Over the next half to 10 minutes, the tube warms up to operating temperature, with a larger amount of ions present and changes in the mixture of metals in the ionized gas (for HID lamps). The older magnetic ballasts would initially supply the voltage needed to strike the arc and then act as a choke to limit the current (otherwise the tube would overheat and explode in a very short period of time. Certain types of HID lamps needed a very high voltage pulse so they have an igniter to do this. Simple types of fluorescent ballasts did not have the additional windings to heat up the cathode heater element at the end of the tube, so they required a starter to help. For lamps in cold environments, the ballast had to supply a higher voltage, so you will see a stated minimum starting temperature for different ballasts.

Ignore HID now and look only at fluorescent. The gas inside is mercury at a fairly low pressure (far into the vacuum range), and when cold you will typically see a few small droplets of it as dark spots along the low side. The low-pressure mercury vapor arc produces ultraviolet light (with only a very small amount of visible in the violet end of the spectrum). This is a "black light" used for theatrical effects, mineral prospecting, ozone creation for water purification, insect trapping, etc. For the rest of us, the inside of the tube is coated with a mixture of "rare earth" chemicals (called phosphors) that will absorb the ultraviolet, moving some of their electrons to a higher energy level. These then decay back down and emit light at some other wavelength in the visible light spectrum--the process is called fluorescence, hence the name for the bulb type. Depending on the phosphors used, the color of light produced can be in a very narrow range of color(s) or can be any of more than 20 different "whites". Certain mixes became popular and were given names such as "cool white" or "warm white" etc.

Now to the ballast: Energy losses and size are the main problems with magnetic ballasts. The ballasts run warm to hot, they usually require a heater inside the tube--kept hot all the time even though the heater is not needed once the lamp has started. For many decades (until outlawed) the capacitor used had PCB's as the dielectric. However, magnetic ballasts are simple and will survive a lot of electrical "insults". In comparison to the magnetic ballast, the electronic ones use switch mode power supplies that are much smaller, This results in an output voltage to the tube that is at a relatively high frequency (10kHz and higher). At these high frequencies, the phosphors on the tube wall are significantly more efficient in their conversion of the UV to visible. The circuit designs for these ballasts allow them to be used for more than one tube size, and/or different numbers of tubes, and with input voltages that can range from 110 to 240+ volts. Unfortunately, electronic ballasts are more complex and subject to failure if too warm or exposed to high-voltage transients.

Fluorescent energy savings are all on the electronic side:

• No loss for heaters in the tubes (wiring bypasses them),
• Much lower ballast losses,
• Equal light output at a lower current flow in the tube,
• Smaller tube diameters are allowed, with greater efficiency.
• With changes in fixture reflector materials and design, a larger portion of the output light actually reaches the work areas.

Add these up and you can achieve energy savings of over 30%.

One other downside to electronic ballasts--unless the ballast is designed with a filter on its input wiring, it will impose significant harmonic loads on the supply circuits. In 3-phase 4-wire wye (or star) connected systems, many of these harmonics do not cancel on the neutral and therefore a common neutral can have a current that is higher than the current in any of its three shared "hot" conductors. On all systems, the harmonics imposed by the electronic ballasts will become additional loads on the transformers and distribution systems. So, look for ballasts that are marked with a high power factor and a low total harmonic distortion "THD".

Hope this adds to your knowledge. --John M.

Arun,

I realized I may not have addressed an important part of your answer. There are basically two types of ballast designs. Everything else is a spin-off of these.

The first type adds power to the coil or electrode in order to heat it up to a point where the work function is reduced. The work function is basically the energy required for the emitter coating to emit electrons into the ionized gas inside the lamp. Some of these ballast only provide heat during the starting stage while others left the heat on during operation. Typically each coil would consume about a watt just to keep it heated. It also let the ballast maker save money on copper but the user paid for it over and over in the form of consumed power. Fortunately, the newer ballasts are designed to use the minimal amount of energy.

The second type of ballast (cold cathode) uses only a single wire to each end of the lamp. Some of the lamps have both wires of the coil twisted together and attached to a single pin on the end of the lamp. These ballasts rely on high voltage to initiate the arc or current flow.

So, which ever type of ballast you pick, there is a ballast factor (bf) rating that controls the current at the level above or below the "design" level. If you look in a catalog at lamps you might see, you will see a lumen rating for that lamp. What is not obvious is that you will only get that level of light with a unity ballast factor (bf=1.00). To increase the light level you want, you need a bf greater than 1. To save a little power, you need a bf less than one. So, you might ask, "Why so many choices?" To which a designer will tell you that when you are planning for a certain light level in all rooms (of different sizes) you will find that the number of light fixtures you need is X.ZZ where the ZZ is the remainder. Well since you can't have a fractional number for a whole fixture you have to round up or round down. Or after you finish laying out your fixtures, you may calculate that there is too much light in one room and not enough in the other. By choosing your ballast factor as you like, you can come a lot closer to matching the light level in each room.

But in reality, humans can not really see that much difference since our vision is logarithmic. So, it is just another way to mess with the power level. Just remember that when you reduce the power level, it also reduces the light level. The point is that you don't get "something for nothing".