On Mon, 18 Feb 2002, Spehro Pefhany wrote:

> >Interesting point -- I could then use a MOSFET and PWM to start the lights
> >soft, then cut 'em back to a soft glow late at night.
>
> The triac and phase control will be more efficient, and probably cheaper,
> and won't look any different.
>
> (Two series diode losses + 1 transistor loss) > one triac loss

True... but then I get into zero-crossing detection, etc...  dimming is
not a primary requirement here.  I just wanted to avoid using a relay for
space & cost reasons (mostly space).  If I can get dimming as a side
benefit, so much the better.

> >  Now I realize how
> >little I know about light bulbs -- these are the little 8W wedge-base
> >landscape light bulbs intended for 12V operation.  Is there any problem
> >using DC instead of AC, and will running them on a low brightness with PWM
> >shorten their life, I wonder?
>
> Wedge base? Ours are automotive style bayonet base (tail-lamps)
> Anyway, the DC thing is pretty much a myth. If they are halogen they
> should be operated at full power for a while periodically to get the
> envelope temperature up. Easy to program with your PIC. ;-)

I don't think they're halogen, will have to look.  Well, maybe some are.
I have mostly the round path lights and a few spot lights for the bushes,
all 8W bulbs but the spots may be halogen.  At any rate, they'd be run
full power for at least several hours a night.  By "DC thing is pretty
much a myth"  do you mean you think they'll run as well on DC as on AC?
I can't imagine why they wouldn't.

Dale

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