Question About Lighting

It's what makes the lights go on.

It makes them "start".

Do some reading.

Ignitors are needed to generate initial high voltage pulse of certain very voltage amplitude and pulse width - to start the lamp ionization process. Only after this the lamp actually starts to glow. It Is similar to starting your car- initially by cranking by a starter motor or in 2 wheelers by a kick start or again by cranking by automated started motor. Even in friction - static friction is higher than dynamic friction. Any phenomena in the world needs higher energy to begin and later can continue to run without that initial pulse.

" Any phenomena in the world needs higher energy to begin and later can continue to run without that initial pulse."

Just taking an issue with the choice of words. As stated, it leads to the false conclusion that it takes more energy to start a lamp than to run it. That is simply not the case.

A cold lamp has high resistance between electrodes initially. And yes, a high voltage is required to begin ionization in the right direction (between electrodes). But, as the gas becomes ionized, the resistance drops dramatically. A properly designed igniter will extinguish as the voltage from electrode drops with increasing current through the gas. So in reality, the power curve is actually a fast ramp. To suggest otherwise would be less than accurate.

Even in cold cathode lamp - as you say initial striking voltage may be even 400V and running voltage as low as 70 to 90V. Now check current during running and current when 400 V is applied. Kindly check VIm = Joules energy in teh short period (even if it is in milisec) and then joule energy during running.

I know for sodium vapor lamp striking voltage may be around 4 KV for just 10 microsec and for metal halide lamps around 2KV for 25 micro sec. But during this striking period lasting even 10 25 micro sec VI is far higher than VI during normal operation. Ballast in series with mains supply is same during running and operation. Ballast is not supposed to saturate under worst conditions of voltage and current. In fact for sodium vapor lamp - randomly generated pulses are adequate, but for metal halide- it should be near the peak of every half cycle(still in the market- you get igniters which generate HV spike only in one half- thus reducing lamp life etc).

I hope you understand - not just voltage, but energy within the pulse. Also do note with a single pulse lamps do not start - there will be many pulses and timing between pulses is also important.

This question comes up from time to time and I do understand that it can be a bit confusing. Sometimes the choice of measurement instruments lead to misinterpretations of the data. But, I have tested very carefully for this and I stand by my original statement.

Yes, I have seen instances of higher than normal current in the microsecond range but they are always accompanied by significant drops in voltage from one electrode to the other, resulting in a net power increase that follows a rapid ramp that sometimes follows an exponential curve.

Consider this: Without the ballast, a plasma type lamp would run away with increasing current until some component fails. I have intentionally induced this effect. But more importantly, if the lamp runaway effect was faster than the ballast, then the ballast would not be able to stop it.

Many times, the mistake that engineers make when taking this kind of measurement boils down to nothing more than knowing how your equipment works. A cheap O'Scope will not be able to track both voltage and current at the same time. That means that you can not calculate the instantaneous power at all. It is a good lesson in appreciating the subtle differences in equipment.

Apply common sense again. A ballast is in series with such lamps during normal operation. Mains supply voltage is vectorily distributed between ballast and the load during operation.

At the time of start up - a starter bimetallic switch across say a tube light just shorts the lamp- which means entire mains voltage peak is across the ballast only. Obviously current is far higher due to momentary short circuit. This energy which is stored in the ballast - is released - resulting in high voltage- when the starter switch opens. This action breaks down the gas in the lamp and ionization takes place. Forget oscilloscope- cheap or expensive. Use common sense, college mathematics and compute the joules of energy etc. After that you write on CR4.

OK, xyz. Let's apply a little common sense to product design considerations. Let's say your igniter malfunctions and welds closed. Now your "excess current" is going to overheat the ballast and burn the house down? Well, not right away because it is not a lot more than normal current. As stated, that "far higher current" at line voltage would cause quite a problem. Oh course that doesn't happen because they always seem to include a thermal cut off (TCO).

And you are still wrong in your understanding of "college mathematics" (actually plasma physics) and the purpose of the temporary short. While V=J/c you can't ignore the dynamic situation caused by a sudden current change (to zero) in a large inductor. The inductor will increase the voltage in attempt to maintain the current flow it had just before the igniter open up and removed the short. With conventional magnetic ballast, the principle is V=L*di/dt and the purpose of the igniter is to produce a sudden change in the current which results in a large open circuit voltage. That does not require a lot of excessive energy as you incorrectly imply. The increased current does assist in creating a little more voltage but the actual increase in current is on the order of around 150% while the igniter is closed. Yes 150% is obviously higher due to the igniter closure but I wouldn't go so far as to refer it as being "far higher".

You should understand that I was trying to be kind about common mistakes made by people using oscilloscopes. It should have implied that I spent many hours making just this kind of measurement and that I know what I am talking about. And, I'm afraid that "common sense" simply won't give you the answers which are very specific and not common at all.

Finally, I'd love to hear what you mean by "breaks down the gas in the lamp". Pray tell, what puts it back together?