On Fri, 03 Jul 2009 21:31:58 +0100, Andy Champ 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 fitted in
>> the dining room. Based on the 12V halogens I have used elsewhere I expected
>> the room would need eight 25 watt lamps. In fact it needed eight 50W ones.
>> 400W to light a medium sized room!

>> I'm now intending to put new lights in the kitchen. Today I lit a 12V 20W
>> lamp and a 240V 25W lamp side by side. Both lamps were the 36deg type.  The
>> 12V lamp was much brighter. I was running it on 12.00VDC, but the current
>> drawn was 1.7A which equates to 20.4W, so I guess the brightness would be
>> the same on a nominal 12V AC supply. The 12V lamp had a neutral colour,
>> whereas the mains lamp was rather warm. I wonder if this accounts for the
>> greater efficiency of the 12V lamp, and means that the mains lamp, being
>> relatively under-run, will last longer.

>> 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 brightness and
>> colour temperature, as near as I could tell.

>> Can anyone cast any light (geddit?) on this? Are 12V lamps really so much
>> more efficient? If so, why?

> The guys over on uk d-iyy will be able to pick this one up.  This is a
> frequent topic.

> Ignore any references to angle grinders.

> Andy