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Re: Power Factor - was Re: Sylvania Quicktronic 32 Electric Ballasts

Scott Hieber wrote:

> Ballast factors are measures of the lumen (light) output of a ballast
> for a given bulb  relative to that bulb on another ("standard")
> ballast.  A ballast might have a higher Ballast Factor than another
> ballast but that might be due to drawing more energy from the power
> line, and therefore passing more energy to the lamp, OR it might be
> because it is more efficient than the other ballast (which means it has
> a higher POWER FACTOR -- it outputs a higher ration of its input energy
> to the bulb).  In either case, the bulb will probably have a shorter
> life given that it is getting more amps and therefore, running hotter
> than it would on a "lesser" ballast.

The power factor is not related (at least in a direct sense) to the
efficiency of a device.

Power factor relates to the proportion of real to apparent power that the
device consumes.  Most of the loads in a household or industrial setting
(including magnetic ballasts) are inductive, and thus have a lagging power
factor.

So what happens for a load that has a lagging power factor significantly
less than 1 is that while the appliance consumes power, the power is
supplied on those parts of the cycle where the voltage is low, meaning that
there is a higher instantaneous current.  Electric utilities don't like
this, as a badly matched load creates higher resistiive losses in their
cables.

That's the reason why luminaires often have capacitors in them.  The
capacitor balances out the inductive ballast, and provides close to unity
power factor.  With an electronic ballast it's easy to maintain unity power
factor using active circuits.

Efficiency is measured by looking at the input power and the output power of
a device.  Any mismatch is a drop in efficiency.  Or even simpler, an
efficient device stays cooler than an inefficient one.  Efficiency is
important in crowded hoods, where the waste heat can't easily escape.

Cheers,

Suzy (who can't help replying on account of being an electronics engineer)

---
Suzy Jackson    http://www.suzyj.net    suzyj at suzyj_net