Message from discussion
TOT halogen efficiency
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From: NT <meow2...@care2.com>
Newsgroups: uk.tech.digital-tv,uk.d-i-y
Subject: Re: TOT halogen efficiency
Date: Fri, 3 Jul 2009 14:08:01 -0700 (PDT)
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On Jul 3, 9:31=A0pm, Andy Champ <no....@nospam.invalid> wrote:
> Bill Wright wrote:
> > Some time ago I reported in this hallowed forum my disapointment at the
> > apparent inefficiency of some mains voltage halogen downlights I'd fitt=
ed in
> > the dining room. Based on the 12V halogens I have used elsewhere I expe=
cted
> > the room would need eight 25 watt lamps. In fact it needed eight 50W on=
es.
> > 400W to light a medium sized room!
partly because theyre (mostly) used in downlighters.
> > I'm now intending to put new lights in the kitchen. Today I lit a 12V 2=
0W
> > lamp and a 240V 25W lamp side by side. Both lamps were the 36deg type. =
=A0The
> > 12V lamp was much brighter. I was running it on 12.00VDC, but the curre=
nt
> > drawn was 1.7A which equates to 20.4W, so I guess the brightness would =
be
> > the same on a nominal 12V AC supply.
performance on 12v ac is identical to on 12v dc
> The 12V lamp had a neutral colour,
> > whereas the mains lamp was rather warm. I wonder if this accounts for t=
he
> > greater efficiency of the 12V lamp,
yes, mains ones generally run at lower filament temp
> and means that the mains lamp, being
> > relatively under-run, will last longer.
quite the contrary. Mains have very thin filaments, so they need to
underrun them to get them to last adequately.
> > I reduced the voltage on the 12V lamp until it had the same apparent
> > brightness as the mains lamp. At 8.7V both lamps had the same brightnes=
s and
> > colour temperature, as near as I could tell.
>
> > Can anyone cast any light (geddit?) on this? Are 12V lamps really so mu=
ch
> > more efficient? If so, why?
yes, thicker filament enables higher operating temp for same life
> The guys over on uk d-iyy will be able to pick this one up. =A0This is a
> frequent topic.
more info on halogens, downlighting, dimming, and bulb life here:
http://www.wiki.diyfaq.org.uk/index.php?title=3DCategory:Lighting
> Ignore any references to angle grinders.
>
> Andy
NT
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