# Ghost Load



## ship (Oct 11, 2006)

At the moment, I’m working on a “ghost load box.” 5:30 tonight the crew for … some tour leaving in the morning came to me and said that their 23w R-40 compact fluorescents were dimming down to about 10% on a Sensor dimmer rack but after that starting to flicker…



I’m like, these fluorescents are getting down to 10% on a stage lighting dimmer system and you are complaining? You should be glad, I would put them flickering out at 30%.



Oh’ no, you don’t understand they tell me, (two crew chiefs) going out would be fine, it’s just that instead of going out, they are acting like strobe lights at low levels. 



Urr, you do of course realize that people would pay good money for an effect like this don’t you, what’s the problem? This I ask tongue and cheek and note my boss asking the same question a few minutes later. 
My boss of course did not take the time to go into a side topic in making people roll their eyes in a "back in the day" type of way such as I in eating up this problem solving attention time I chose to waste or pull the crew chief's tails of further. Back in the day when I applied for a job here, I took with me these random strobe light fixtures I made as a sort of show in tell. A fluorescent starter in series with a incandescent lamp. Yep, it was cool I mastered what wattage of lamp would be good with each type of fluorescent starter and in part now why I'm called the shop fabricator. Didn't help solve the problem but did annoy all about sufficiently this side light. I enjoy such things so as to break the stress of solving problems or at least pull tails. 

Also wasted more time in noting how letting them strobe was not really good for the lamp life of the lamp, than again also neither is dimming the lamps really good for lamp life. "That's ok, we have double the spares on them..." They don't really get the joke of a fairly cheap and 20,000 hour lamp needing to last for a fairly short rock tour... I'm on the other hand curious about them getting double spares for this lamp.





Anyway we get down to business. First we confirm on a variac rheostat dimmer that it does flicker out and go out completely at 30%. - These lamps like the electronic dimming but seemingly their wattage is low enough that when there is too little power, the internal starter keeps attempting to strike an arc. Attach some wattage of incandescent light to the load and it no longer flickers at 10%.





Long story short, we are adding a 40w incandescent lamp in line with each fluorescent so as to load up the dimmer more and not make it act funny at low dimmer intensities. Lamps go out at 10%, all is good except the tour leaves in the morning and I get to make a seven channel incandescent resistance, double baffle black box so no light leaks out yet the fluorescents get some ghost loading on the dimmers.



Strange stuff, fun career.



Who can explain the how and why's both of the reostat dimmer causing the lamp to go out at 30% and why a ghost load was necessary for the Sensor rack on these 23w compact fluorescent lamps?

This much less beyond observations above the how and why of this few minutes of humor for me?


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## koncept (Oct 26, 2006)

Guessing here, is that the florescents see balasts loose their charge so it thinks the light was just turned on and attempts to restrike the lamp. adding the ghost load to the dimmer circuit keeps more current being drawn which keeps the lamps on and they do not think that they should be restruck

other than that im not sure...

i have heard of using the started for florescents to make strobes and flicker boxes but have never tried to do that... i think it would be a good effect with some 4ft tubes though...


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## VeeDubTDI (Nov 14, 2006)

Theatrical dimmers have trickle currents that run through them. This current is enough to power the starter on the fluorescent lamp. Adding incandescent lamps to the circuit absorbs this trickle current. This same trickle current will power the neon "lamp out" indicator on top of Altman MR-16 Zip Strips even when the dimmer level is at 0%.

Were they using the "dimmable" compact fluorescents? If not, then that would explain why they die at 30%. The ballasts aren't made to run on 40 volts and the lamp dies. Dimmable CFs will operate down to ~10% without going out... they turn really purple though.


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## ship (Nov 14, 2006)

they were using dimmable fluorescents but after 10%, in fact at 0% once out they were attempting to strike but there was not sufficient power to maintian the arc.

Very good by the way.

So now what if you say had a bunch of 50w incandescent lamps (one per channel) on the same ETC Sensor dimmer pack?

What sorts of problems if any might be expected?


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