[Shop-talk] tube fluorescent wattage

[Randall]

> (all with 40 watt bulbs)

Regular start, rapid start or instant start?

> Interesting results, I think.

That is interesting.  Thanks for the report.

> I actually expected them to consume 
> more than the bulbs were rated assuming some inefficiency in 
> the ballast, and I expected the old magnetic ballast to 
> consume more than the solid state one.

Me too.  But it makes sense to me that old bulbs draw less current, so I'm
still wondering how much power was actually making it to the bulbs.  That
seems to me to be the way they usually fail, apparently the bulbs lose gas
and the current drops until the ballast can no longer hold a plasma through
the tube.  For bulbs with filaments, then the filament burns out from the
ballast having to constantly restart the tube (hence the flicker of a dying
fluorescent).  Instant start bulbs just keep restarting until either the
ballast dies (from the constant restarting) or the bulb finally won't light
at all.

> I always wondered what was happening power-wise when magnetic 
> ballasts were flickering upon startup -- they are using very 
> little power until they warm up and reach full-illumination.

Depends on the bulb type, I think.  Regular start bulbs (the ones with a
separate starter to replace) should be drawing filament power; while I think
the others would be drawing nothing at all.

> Just to see if my Kill A Watt was reading low, I tested a new 
> 75 watt incandescent, and it showed 77 watts, so I think it 
> probably is close.

Agreed.  But it would be interesting to test a larger selection of new
bulbs, to see how much variation there is.  I doubt they worry much about
getting it exact.

Randall