Hi everyone, I am becoming more interested in fluorescent lighting.  I have never built my own fixture, and I'm curious about some terminology associated with linear fluorescents and their ballasts and fixtures.

I have a few questions:

1. What is the difference between preheat, rapid start, and instant start? Can the same fluorescent tube (i.e. a Philips Alto F40T12) be run on any of the three main ballast types?

2. What does "HO" stand for in fluorescent nomenclature?

3. Is a preheat fluorescent and a magnetic ballast fluorescent the same thing? 

4. How can I tell which ballast will run which lamp or which lamp will run on which ballast?

Thank you for your help and I look forward to learning more about fluorescent technology!

1. Instant start use one wire to each end of the lamp, thus start the lamp cold. Rapid start heats the filament before, during and after starting of the lamp by using a heating transformer coil. Preheat using a starter to preheat the electrodes and make a HV pulse from the ballast to start the lamp. Preheat is the standard topology in 220-240V countries, as they uses series chokes.
2. HO = High output.
3. Yes. But rapid start is also magnetic, and there are instant start ballast which are magnetic as well.
4. Compare the lamp voltage and current, to the ballast lamp voltage and current.

1. Instant start use one wire to each end of the lamp, thus start the lamp cold. Rapid start heats the filament before, during and after starting of the lamp by using a heating transformer coil. Preheat using a starter to preheat the electrodes and make a HV pulse from the ballast to start the lamp. Preheat is the standard topology in 220-240V countries, as they uses series chokes.
2. HO = High output.
3. Yes. But rapid start is also magnetic, and there are instant start ballast which are magnetic as well.
4. Compare the lamp voltage and current, to the ballast lamp voltage and current.

Thank you dor123!  That is very helpful! 

1. Instant start is used chiefly with slimline lamps and electronic ballasts (not all electronic, see below). Most magnetic ballasts that have no starters and that have two leads to each lamp end are rapid start (or trigger start which is similar in lots of ways). Like dor said, if there is a starter, it is preheat. A starter is usually in a small replaceable canister but not always. Some starters are inside the luminaire and not replaceable. When they start, the ends of the lamp light first, and usually the whole tube strobes a few times before lighting. You'll also hear pinging sounds when the lamp flashes.

Regarding lamps, save for the slimline lamps that have shunted electrodes in the end caps, most are interchangeable. Some work better than others, the main difference being the cathode voltage rating. Using the wrong type of lamp usually kills the lamp faster than the proper one and usually does not harm the ballast.

3. Some electronic ballasts have circuitry to preheat the electrodes before striking the discharge. To differentiate them from standard preheat, they are called program start. The circuitry senses when the lamp has preheated sufficiently then strikes the lamp. Success is achieved most of the time. This is different from preheat where the starter tries to strike the lamp at somewhat random intervals in hope of striking the lamp successfully in rather short order (resulting in a series of flashes). This is different from instant start because it takes about 1 second to strike the lamps.

4. Most ballasts have labels that list which lamps can be operated with it. Some ballast/lamp combinations not listed work as well while others, not so much. If it is not listed, experimentation is the best way to find out.

Thank you for the information!  I'm still learning the basics of fluorescent installations and I might build my own fixture sometime soon.  I'm thinking about doing something with a small lamp, such as an F20T12 (i.e. GE Kitchen and Bath).  I'd like to build a fixture that I can use on a practical basis.  We'll see...

Another thing I've noticed is the nomenclature and how sometimes the length in inches matches up with the wattage, and sometimes it doesn't.  For example, an F40T12 is 40 watts and measures 48 inches.  Is the "40" in F40T12 always the length and not necessarily the wattage?  Would a 6 foot lamp be an F72T12, for instance?

Is it true that instant start setups shorten the life of the fluorescent lamps?

Which setups allow for two lamps in tandem to continue to light when one of the lamps burns out?

Thanks for all the help 

In North America, the number is usually the wattage. F40 lamps are 40 watts, F15 are 15 watts, etc. The exception is the high output and very high output in which the number is the length in inches. F48 HO lamps are 48 inches and 60 watts. When HO lamps are identified in inches, they are a couple of inches shorter than stated length. The fixture in which they fit is the length stated on the lamp. F48 lamps fit in a fixture that measures exactly 48 inches.

The other exception is circline lamps when the FC is followed by the diameter of the circle. FC8T9 lamps are 8 inches across in diameter. They are usually 22 watts.

Instant start setups do reduce the life of the lamps when they are frequently switched. Think of an instant start setup in a washroom. They do prolong the life of the lamp if they are rarely switched, such as 24/7 setups. Even with 6-8 hours per start, they perform quite well with daily used lamps lasting almost 10 years sometimes. Program start has a 'soft start' and is better suited for frequently switched applications.

Normally, rapid start is always in series. Both lamps dim when one is EOL. The other lamp comes back to full brightness when the EOL lamp is replaced. Same goes for taking out a lamp. Instant start (whether magnetic slimline or electronic) are usually in parallel. When one lamp goes out, the other one stays lit.

In North America, preheat is almost always single lamp per ballast. In Europe it is (was) common to wire up two 20/18W lamps on a single 40/36W ballast, in series (much like Christmas lights), each lamp having its own starter loop. Each starter is 120V rated instead of 230V for single lamp. When one lamp reaches EOL, depending on what happens to the electrodes or the starter, you have a myriad of possibilities. If the bad lamp gets its starter stuck, the good lamp continues to light with slightly higher current and the bad lamp is stuck in preheat mode. If the bad lamp blows a cathode, both will go out. In some cases, when the bad lamp's starter is still good and flashes the lamp trying to light it, it makes the good lamp flash as well. That can (will) cause premature failure of the good lamp's starter and electrodes.

Even another configuration is North American 3-lamp troffers. They typically have two ballasts, one single lamper and one 2-lamper. They are often separately switched so a bad lamp on one ballast will not affect the other lamps on different ballasts.