Author Topic: Flickering Fluorescent Lights On A bus.  (Read 9052 times)
Fox Mantra
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Flickering Fluorescent Lights On A bus. « on: September 24, 2010, 11:07:11 AM » Author: Fox Mantra
OK was sitting on the bus going home yesterday and this was happening all through the journey xd.

http://www.youtube.com/watch?v=iR4YvqZP8aM
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Re: Flickering Fluorescent Lights On A bus. « Reply #1 on: September 25, 2010, 12:26:26 PM » Author: dor123
Why this lamp turned on/off several times in this movie?
I saw an F13T5 near EOL in the past, in a bus on a bus line no. 165 to the central station of "Merkaziat Hamifratz" near Haifa. The lamp was filckered wildly like an F96T12 HO on a HPF rapidstart ballast or a hollow cathode sign on a NST at their EOL.
I usually don't photographing inside a public transportation, to prevent the passengers to look at me.
In most of our buses, the fluorescents instant starts when they're turned on.
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Re: Flickering Fluorescent Lights On A bus. « Reply #2 on: September 25, 2010, 01:08:28 PM » Author: Fox Mantra
to be honest i think its a dodgy wire somewhere within the bus, as every time the bus slowed down or over a bump it made them flicker.  these are rapid start ones as when the drivers switch them on there on almost instantly. 
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Re: Flickering Fluorescent Lights On A bus. « Reply #3 on: September 25, 2010, 10:19:14 PM » Author: RCM442
I noticed something about those, the cathodes are ALWAYS heated, despite the lamps being lit or not, must be to keep it so they are always instant start...
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Re: Flickering Fluorescent Lights On A bus. « Reply #4 on: September 26, 2010, 01:28:21 AM » Author: Medved
It indeed look like loose 24V power wire.
Here bus ballasts tend to be RS (in buses especially F20T12 - these had troubles with F18T8, mainly in winter), but those installed since mid 90's are all programmed start using PL-L 18W lamps. I've never seen instant start fluorescent ballasts here - i guess mainly because they have very poor lamp cycle life, especially when the light is cycled On and OFF every stop the bus made (to light the passenger paths on these stops, but do not cause disturbance to the driver during driving)
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Re: Flickering Fluorescent Lights On A bus. « Reply #5 on: September 26, 2010, 10:07:04 AM » Author: sparkie
Most bus lights tend to be HF electronic, on the buses round here you can see the striations when the door light goes on at a stop.

The behaviour of those lights in the video is a frequent occurrence on Tube trains in London. The lights in each carriage of the train are supplied from the DC third rail via a 'shoe', which temporarily disconnects whenever the train goes over a set of points. During the few seconds of power loss most of the lamps go out, with only the battery-backed emergency lights remaining lit. Can be quite scary if you don't know about it as you are deep underground in a tunnel and it is a bit dark! :o
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Re: Flickering Fluorescent Lights On A bus. « Reply #6 on: September 26, 2010, 12:44:10 PM » Author: dor123
Most of our buses fluorescents lights are operation much like fluorescents in emergency lights, but without the underdriving. They are probably uses by either magnetic ballast for DC battery voltage and a seperate inverter, like the fluorescent emergency lighting, or by DC operated instant start electronic ballasts. There is no preheating of the electrodes, at all during ignitions. Most of them are T8s, but several of them i saw also F13T5s.
The lights that operated in our buses only when the door opening, are all incandscents or halogen.
« Last Edit: September 26, 2010, 12:46:30 PM by dor123 » Logged

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Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

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Re: Flickering Fluorescent Lights On A bus. « Reply #7 on: September 26, 2010, 04:39:32 PM » Author: Medved
@dor123: All "electronic" ballasts are in reality principally same as "magnetic" (to be more exact "resonant start") fed by inverters, only the main "magnetic" ballast part is designed to operate at high frequency (instead of usual 50/60Hz), so related components (coil and the capacitor) are small and have nearly no losses (<0.5W for 36W lamp) - this is the main reason for overall ballast being so efficient and lightweight.

The 24V fed ballasts i've seen are usually of an RapidStart concept (newer use programmed start, but those are way more complex), they only feature filament power boost before the lamp ignite (it is intrinsic to most simple designs; it provide ~7..8V for filament before and <3V after ignition), so it take fraction of a second to heat electrodes up to the ignition point, but the lamp does not ignite without this heating.
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Re: Flickering Fluorescent Lights On A bus. « Reply #8 on: March 06, 2011, 10:09:43 AM » Author: seansy59
I saw something similar happen at my doctors office. The troffer above the door (Magnetic rapid start 4 bulb F40T12). Everytime the door closed, ALL the lights flickered rapidly, on then off, and started normally again by themselves, all within about 3 seconds. Now, we ALL know thats a short circuit, whether its the AC line going into it, or a ballast or socket wiring short. Not only is it a shock hazard, but a fire hazard too! We told them, and they said "Oh, the bulb is just burning out probably"  >:( I tried ::) Still the same way, I saw that about 7 months ago, and went back a few days ago, STILL the same, except the bulbs are getting dimmer and blacker at the ends from the constant start/restart.
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Re: Flickering Fluorescent Lights On A bus. « Reply #9 on: May 18, 2015, 12:29:39 AM » Author: Solanaceae
They may be powered by modified sine wave inverters. Those cause an annoying flicker and problematic start with preheat chokes.
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Re: Flickering Fluorescent Lights On A bus. « Reply #10 on: May 18, 2015, 01:41:35 AM » Author: Medved
They may be powered by modified sine wave inverters. Those cause an annoying flicker and problematic start with preheat chokes.

This is never used in a fixed installation, maybe desk lamp connected to an outlet intended for a TV, but never the permanent lighting installation in the vehicle.
The modified sinewave is rather complex to generate (compare to just a rectangle) and it is done so only for the connection of an electronic equipment designed for normal mains (to have the same peak and rms value) and behaves badly with most ballasts. If standart preheat fixtures are supposed to be used, way simpler and way better performing is to generate just a rectangle at higher frequency, so the ballast currents will match. Or the even older systems use rotary inverters and those generate real sinewave. But I don't think those centralized inverters were ever used in buses, I would expect them just in trains. In buses were used either just incandescents, or later local high frequency inverters (each lamp has separate inverter).
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Re: Flickering Fluorescent Lights On A bus. « Reply #11 on: May 18, 2015, 09:04:26 AM » Author: hannahs lights
When I tried to look at the video it said that the account is suspended any other way I can see it please?
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