Why are projector/ spotlight bulbs 82 Volts?

guess that could get ugly if you don't balance the number of lamps going each way

here in 240V land I've seen quiete a few that uses 120V lamps in series, wonder if it is because the thicker filament in a 120V lamp is more robust

-Lasse

"Clifford Heath"

..... Phil

"Mark"

All the products I found incorporated a 120 to 82 volt step down transformer (very likely an auto-transformer) to supply the lamp.

Pretty common for projector lamps and follow spots that do not get long hours of continuous use.

..... Phil

Yes, that is correct. The lower design voltage results in a shorter thicker filament. For a given life expectancy, a shorter thicker filament can be operated at a higher temperature - inmcreasing percentage of its radiation bgeing visible rather than infrared. Along with making the color of the light slighter whiter, and the filament slightly more rugged against vibration and mechanical shock.

Add to this - the shorter filament is a more compact light source whose output is easier to concentrate, direct, etc. with optics than is the case with a longer filament.

It appears to me that maximizing "overall luminous efficacy" of incandescent lamps, when design voltage is the variable, favors design voltages of:

~5-6 volts with vacuum fill when design power is near or under 1 watt

~6 volts with singly coiled filament and gas fill when design power is a couple to a few watts

~12 volts with singly coiled filament and gas fill when design power is ~10-75 watts

Somewhere between near-28 and 82 volts with coiled-coil filament and gas fill, some chance closer to 28 volts than to 82, when design power is in the 100's of watts

Designing for lower voltage increases a heat conduction loss through the ends of the filament.

-------------------------

How is the circuit more complicated with a triac than with an SCR?

Meanwhile, it appears to me that due to greater popularity and according production volumes, triacs in sizes good for line voltage incandescent lamp dimmers don't cost much more than comparable SCRs do.

I have seen some 120V projectors with 82V-rated lamps, and too compact and too lightweight to have a 400 or 600 VA transformer, even if such a transformer is an autotransformer needing about 30% of that changed in voltage.

Furthermore, the 82V rating is fairly obvious about unfiltered halfwave rectification of "117"-120 VAC, in 60-Hz land. The lamp filaments involved tend to be thicker heavier ones designed mostly for 300-plus watts, often 600-plus watts.

Further improvement appears to me likely available by designing for a voltage lower than 82 volts, due to considering performance of both 28V and 82V design voltage lamps with coiled-coil filaments and design power in the 100-400 watt range. Accordingly, lack of incandescent lamps designed for voltages higher than 28V and lower than 82V indicates to me that the 82V lamps were originally designed with diodes rather than transformers "in mind".

It does appear to me that a diode used to accomodate an 82V lamp to

Set your PC's clock correctly, ya dopey ditz.

Thanks. This box has almost no networking, just NNTP via a proxy. That means no NTP.

"Don Klipstein"

Remember, it is fan cooled and drops 38 volts at 4.4 amps.

ALL the products I found on a search used such a tranny.

Oh how in love with out our opinions we are...

..... Phil

I'm guessing they originally used rheostats. Once, when in high school (ca.

Cheers! Rich

So, what _is_ the answer? It does no good to simply run everyone down without providing an alternative.

IOW, If Clifford's answer is wrong, then what _IS_ the right answer, or do you just get off on sitting spewing "NONSENSE" at everyone?

Thanks, Rich

Probably because they can easily be controlled by an SCR phase-control circuit, instead of the slightly more complicated and expensive TRIAC one.

Clifford Heath.

One need have no idea at all what the *real answer* is to KNOW beyond any doubt what is not.

Simple logic.

Way over your f****it, pointy head.

.... Phil

SCR is easier if you have a remote voltage control instead of a pot. But as has been pointed out, that's probably not the reason.

Phil Allison wrote: > ** Irrelevant.

That answer sure is a beauty in the troll repertoire.

Thanks for proving you are trolling.

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Don,

ok thanks I will try to determine if this particular follow spot has a transformer or a diode. I got a glimpse inside the other day but we were under duress.

I KNOW it has a fan and I suppose it is possible that the fan motor has extra windings to double as a transformer. The cold turn on surge current must be huge and that would be an issue for a series diode. I'll try to get the model number and try to find a manual and will report back here in a few days.

Mark

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its a Chauvet 400 follow spot

its does have electronic dimming so my guess is it is a standard triac dimmer that is limited in the upper range

Mark