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?