🚀 go-pugleaf

"Paul Bealing" <paul@pmb.co.nz> wrote in message
news:Fz6da.6118$8b.720573@news02.tsnz.net...
> Klaus Vestergaard Kragelund wrote:
> > "Paul Bealing" <paul@pmb.co.nz> wrote in message
> > news:TINca.5877$8b.679066@news02.tsnz.net...
> >
> >>DaveC wrote:
> >>

snip - snip

> >>>I've been asked to help light a small office building hallway. The
> >
> > Buy lamps with greater power rating and reduce the voltage. This will
give
> > you way longer lifetimes if you can live with the more "warm" spectrum
of
> > light they emmit when driven this way.
> >
> > Cheers
> >
> > Klaus
> >
> >
> We have operated lamps at less than 100% and with a soft-start to reduce
> initial shock. Experience over the past 6 years has indicated that the
> failure rate has still been higher than expected.
>
> If you run a QH at much less than 100% for long it develops a black
> coating on the inside. QH require periodic full power operation to raise
> the temperature and restore the deposited tungsten to the filament.
>

Correct. I just went back to my source (my father has specified hundreds of
such systems in Denmark). This is what he has to say:

Below 87% drive voltage the black coating will start. This is not damaging
to the lamp however - just run it at 100% for an hour and the lamp is
restored to the original state.

It is common in the industry to run a 12V system at 11.3V (94%) and at this
level the coating will never start. In fact, he says, an entirely specific
transformer is used 230V/11.3V - that has been designed only for QH systems.

Lifetime: Running at 94%, in his experience the QH shows a prolonged
lifetime of 3-4 times. But of course the lower power means less light
output. Not at 89% though (0.94x0.94), but less. Because the QH is less
effective at lower temperatures. He uses flourecendt tupes whenever
possible.

Also, the QH is highly sensitive to mains flicker (eg exceeding 100% at
short intervals). Often special "electronic transformers" (I gather some
form of triac control) are used to limit the maximum power delivered to the
lamp. These also comes handy when/if one lamp dies. Due to the resistance of
the wires and the regulation of a normal tranformer the other lamp voltages
will rise. The electronic transformer will kick in here too to limit the
power to 94% at all times

I guess mains flicker would be a major problem in the USA, don't know about
New Zeeland/Australia. In Denmark it happens were seldomly in residental
areas.

Cheers

Klaus