Had a rather interesting (compared to the lecture) occurrence at uni
today. An 8 foot fluorescent tube started to flicker. Everyone
noticed it, I initially thought voltage sag, but it carried on. It
went off, did its glowing purple/orange at one end trick, re-lit,
probably repeated that once a minute for 10 minutes. Then it buzzed
loudly and got brighter at the end that was dying. The brighter part
spread about 2 feet down from the end that had been glowing purple,
then it just died. No more flickering tube!
I'd never seen it happen that quick before. The other end had no
apparent symptoms or blackening to the phosphor. Mind you, at home,
when a tube in a pair begins to die I will notice it, switch it off
and remove the starter before replacing the tube asap.
Related (lecture rooms): how much neglect can a VGA projector take in
the air filter department? They all seem to flash up messages when
powered on saying 50/100hr clean due, or check airflow. 50 hours isn't
a lot when left mounted on a ceiling!

On May 19, 4:30*pm, Part timer wrote:
Had a rather interesting (compared to the lecture) occurrence at uni
today. *An 8 foot fluorescent tube started to flicker. Everyone
noticed it, I initially thought voltage sag, but it carried on. It
went off, did its glowing purple/orange at one end trick, re-lit,
probably repeated that once a minute for 10 minutes. Then it buzzed
loudly and got brighter at the end that was dying. The brighter part
spread about 2 feet down from the end that had been glowing purple,
then it just died. No more flickering tube!
I'd never seen it happen that quick before. The other end had no
apparent symptoms or blackening to the phosphor. Mind you, at home,
when a tube in a pair begins to die I will notice it, switch it off
and remove the starter before replacing the tube asap.
Related (lecture rooms): how much neglect can a VGA projector take in
the air filter department? They all seem to flash up messages when
powered on saying 50/100hr clean due, or check airflow. 50 hours isn't
a lot when left mounted on a ceiling!

you need to get out more.

On May 19, 6:05*pm, misterroy wrote:

you need to get out more.

Oh trust me I do. Just not today! I spent too long in the same room
and compared with what normally happens the light did the decent thing
and died. Just wondered if anyone else on here had experience of the
same.

Part timer wrote:

Related (lecture rooms): how much neglect can a VGA projector take in
the air filter department? They all seem to flash up messages when
powered on saying 50/100hr clean due, or check airflow. 50 hours isn't
a lot when left mounted on a ceiling!

No it's not, but the lamps run really hot and if the filters get clogged
(as they will because they're quite fine) air flow will be reduced to
the point that there's a risk of the heat from the lamp melting the
innards and/or starting a fire. Consequently, the firmware has
temperature monitoring and will shut the lamp down in the event of
overtemp. On some projectors, they won't fire up until you do a service
reset of the overtemp condition; others will fire up from cold, but turn
off after an increasingly short period. Either way, blocked filters
ultimately means an unserviceable projector.

On May 19, 6:52*pm, Dave Osborne wrote:
Part timer wrote:
Related (lecture rooms): how much neglect can a VGA projector take in
the air filter department? They all seem to flash up messages when
powered on saying 50/100hr clean due, or check airflow. 50 hours isn't
a lot when left mounted on a ceiling!

No it's not, but the lamps run really hot and if the filters get clogged
(as they will because they're quite fine) air flow will be reduced to
the point that there's a risk of the heat from the lamp melting the
innards and/or starting a fire. Consequently, the firmware has
temperature monitoring and will shut the lamp down in the event of
overtemp. On some projectors, they won't fire up until you do a service
reset of the overtemp condition; others will fire up from cold, but turn
off after an increasingly short period. Either way, blocked filters
ultimately means an unserviceable projector.

Interesting that UK fluorescent fixtures still use 'starters'?
Here (eastern Canada) with 115 volt lighting and wall outlet circuits,
and mainly 34 and 40 watt four footers and various other sizes there
are either a conventional ballast or an electronic one, in all/most
fixtures.

Only starters have seen are in very old (50 year?) style fixtures! Got
a couple of them around to rebuild.

But is it because of the 230 volts (peak v. being around 320 v) that a
ballast is unnecessary to 'strike' the arc?

BTW we obtained a couple of 347v fixtures from a being renovated
s.market, they each contained a conventional looking 347v ballast
(most likely 3 phase!) no starters, which we removed and in place
installed 115v ones. They plus another couple of fixtures found dumped
in a quarry have been fixed up cosmetically and electrically and are
now part of a relatives home garage.

Just curious!

In article ,
terry writes:
Interesting that UK fluorescent fixtures still use 'starters'?
Here (eastern Canada) with 115 volt lighting and wall outlet circuits,
and mainly 34 and 40 watt four footers and various other sizes there
are either a conventional ballast or an electronic one, in all/most
fixtures.

Well, starters work fine on 240V even for 8' tubes.
They are used in all 240V countries.
There is increasing use of electronic ballasts, but
they aren't as reliable or cheap as switchstart ballasts,
which pretty much never fail.

I can't tell from what the OP said if the fitting in
question was switchstart - that's less likely in a lecture
theatre (whatever the age of the lighting installation).
My best guess from the symptoms would be SRS (semi-
resonant start).

Only starters have seen are in very old (50 year?) style fixtures! Got
a couple of them around to rebuild.
But is it because of the 230 volts (peak v. being around 320 v) that a
ballast is unnecessary to 'strike' the arc?

340V will strike an 8' tube with preheated cathodes, so no
voltage spike is required on 240V mains. On 120V mains, a
switchstart circuit relies on the back-EMF generated when
the starter opens to strike the tube, which makes switchstart
much less effective on 120V (starter doesn't always open at a
point in the mains cycle when there's current flowing, so it
doesn't work as well for you as it does for us). Also, you can't
drive tubes longer than around 3' because there just isn't the
voltage headroom for the series ballast without using a step-up
transformer (which used to be done on 120V). Nowadays, a 120V
ballast is more likely to be a leakage reactance transformer,
which generates around 600V open circuit, but also limits the
current flow, and this is cheaper/simpler to make than a step-up
transformer and a (separate) series ballast, but not as cheap,
simple, and reliable as our 240V series switchstart ballast.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article , Andrew Gabriel
writes

Well, starters work fine on 240V even for 8' tubes.
They are used in all 240V countries.

I remember seeing what must have been 12ft tubes at Paddington station
about 30 years ago. They were mounted way high up on the passageway
that divides the station and were not very bright at all. Wonder how
they got started, must have needed a helluva ballast.

--
(\__/)
(='.'=) Bunny's thinking about giving Windows 7
(")_(") a go despite what he's said about it...

In article ,
Mike Tomlinson writes:
In article , Andrew Gabriel
writes

Well, starters work fine on 240V even for 8' tubes.
They are used in all 240V countries.

I remember seeing what must have been 12ft tubes at Paddington station
about 30 years ago. They were mounted way high up on the passageway
that divides the station and were not very bright at all. Wonder how
they got started, must have needed a helluva ballast.

Sound like cold cathode tubes.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On May 19, 10:19*pm, terry wrote:
On May 19, 6:52*pm, Dave Osborne wrote:

Part timer wrote:
Related (lecture rooms): how much neglect can a VGA projector take in
the air filter department? They all seem to flash up messages when
powered on saying 50/100hr clean due, or check airflow. 50 hours isn't
a lot when left mounted on a ceiling!

No it's not, but the lamps run really hot and if the filters get clogged
(as they will because they're quite fine) air flow will be reduced to
the point that there's a risk of the heat from the lamp melting the
innards and/or starting a fire. Consequently, the firmware has
temperature monitoring and will shut the lamp down in the event of
overtemp. On some projectors, they won't fire up until you do a service
reset of the overtemp condition; others will fire up from cold, but turn
off after an increasingly short period. Either way, blocked filters
ultimately means an unserviceable projector.

Interesting that UK fluorescent fixtures still use 'starters'?

You mean rather than switch to something more complex and less
reliable?

I'd say we have it about right.

MBQ