Jim wrote:

> Now the contest comes down to zero-crosing start for
> a bulb as opposed to simple 'ballasting' with a
> fixed resistor - although the resistor, by lowering
> the operating temp of the filament, will also work
> to lengthen the life of the bulb ...


Hi Jim, the resistor will WIN this contest. :o)
60w 240vac bulb filament is about 60 ohms cold,
which will dissipate close to 2kW at cold turn on.
The filament does not heat fully in one half-cycle
and even with a zero-crossing turn on device the
filament will get almost 2kW the first half-cycle,
reducing for each half cycle over the first 10 to
20. But yes, that will be SLIGHTLY gentler than
turn on at wave peak.

The resistor will give longer life than just using
zero-cross turn on. But won't compare to proper
soft-starting like many dimmers that slowly ramp the
average voltage to the bulb over 1 second etc.

I also don't like the soft-start thermistors, power
thermistors undergo significant mechanical and thermal
stresses everytime they start up (heat up) and are
one of the least reliable devices i've come across.
Yes the bulbs may last longer but the thermistors
will self destruct.

I have a incubator using a 100w light globe and a
resistor dropping 7% average volts, even with the
nasty 240vac supply we have here (often sees 255v)
the thing has gone for many months switching on/off
every few seconds. :o)
-Roman

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