>> You probably need about 10% losses to stabilise a series
>> string - maybe more depending on required tolerable 
>> voltage
>> variations.
>>
>> A linear constant current source is better power wise 
>> than a
>> resistor for variable voltage,
>
> Umm, mains is mostly fixed in voltage, so a linear 
> regulator will have
> very little benefit.

Mains voltage tolerances have to be allowed for. With fixed 
resistors you must allow enough head room for stability at 
the lowest legal mains voltage and be able to handle 
dissipation at the highest. For an eg 230 VAC nominal supply 
here that's maybe 210 VAC - 250 VAC to be really safe. *IF* 
you have 10% headroom at 210 VAC then that's maybe 12% + at 
250 VAC.

You can run LEDs with much less headroom in the series 
resistors, but longevity will suffer.

> But at what cost? Say instead of 90% efficiency you get 
> 95% with a buck.
> Considering how little power these things need to begin 
> with the energy
> savings is almost trivial.

As they can sell a CFL with SMSPS supply therein for under 
$2NZ when they wish then, not much.

The power needed for incandescent replacement is about 20 
Watts. About 5 of the existing larger units.

> Couple that with something that people ALWAYS

always?

> forget: how much more
> energy is need to PRODUCE and DISPOSE of the buck 
> converter components,
> verses a simple resistor? The amount of energy something 
> uses during
> it's lifetime isn't just the power used to operate it, you 
> MUST include
> the "lifecycle", the energy needed to produce it, and to 
> properly
> dispose of it.

The invisible hand says that production energy cost is < to 
<< purchase price.
And common sense says (BWWIK) that disposal cost also < 
buying ccost.


        Russell

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