Hey I did a wattage test on my junk 160 watt Rite-Aid Self ballast bulb that was made in China....I plugged it to my meter......turned it on......it started at 190 watts......which is higher than the rated watts........and it stayed at 190 watts for about 30 sec to a minute......then the arc tube fired up and the wattage started going down slowly
from 190 to 180 to 170 to 160 and the wattage stopped at 155  watts.......then about 5 min later it became 153 watts.....

any scientific explanation for this? Why it started at higher wattage and went down?

I am interested in hearing the facts from others but I am also interested in the style of how well Max and James explains facts!

Thanks!

-Jace

On starting all voltage is across ballast ( in this case filament) and as arc tube warms up ballast current drops. As to the drop in power output most lamps are approximate power, never seen a fitting that drew exact power as advertised, but most are within 10% of rated

A self ballasted MV lamp is a resistive series-circuit composing of an arc-tube and filament. And in a resistive series circuit, the supply voltage has to be divided up among all the components while the current would be the same.

On start up, the arc-tube has the lowest voltage across it, therefore, the filament has to have the highest voltage across it. And when you increase the voltage of a filament, the current increases. And when current increases, the wattage will increase.

Wattage is VOLTS times AMPS across a resistance...in this case a filament and arc-tube.

As the arc-tube heats up, the voltage increases across it, and that DECREASES the voltage across the filament. That then decreases the current, which will actually decrease the current of the whole bulb, which will decrease the total wattage.
 

I want to know what Rite-Aid sells self-ballasted MVs! The last such one I ever saw sold in a drug store was a GE Time-a-Tan lamp in the '70s!

That lamp Jace speaks of is a Plus Rite not a Rite Aid (thats a funny one!)

Therefore you can't buy these at Rite Aid drugstores!  Ebay is the source of these...

what is the kelvin color ?

for my clear merc  its warmer than just a regular clear merc......it would be a mixture of clear merc and the incandescents....


however a coated one would be more closely the correct color of a regular coated merc

ok thx i came across a box of them its weird looking when lit

ya know i almost bought some SBMV's,cause i thought,yay!...no Ballast..but when i found out that the efficency was lower than regular mercs,that went down the drain fast...i like Pure Mercs the best,although i might get some in the future just to try Em'out!:)

It's 120V or 230V lamp?
120V at startup effectively short the arctube by bimetal switch, to heat electrodes (auxiliary heaters connected in the circuity, but with rather low voltage drop), so the power correspond to filament resistivity only, so it's high.
Then the bimetal switches OFF, connecting cold arctube in series, so wattage reduces by ~20%.
Then the arctube warm-up, so the pressure and consequently voltage over the arc rises, giving less voltage for the incandescent filament, so the current (and wattage) go down, till it settles.

EU 230V versions contain only the filament and "regular" MV arctube, but even there the power input after turn ON is higher, as the cool lamp keep more voltage for the filament.
When the arctube warms up, the power input will settle to the nominal (assuming supply voltage is nominal)

So both exhibit higher consumption after power up, while on 120V version this difference is much bigger.