Most modeling lights allow lighting with variable intensity. What technology do they use for that?

Is it voltage reduction, some kind of AC throttling?

  • \$\begingroup\$ I'm voting to close this question as off-topic because it's about designing simple electrical circuits, not photography. \$\endgroup\$ Commented Oct 28, 2016 at 14:17
  • \$\begingroup\$ @JamesSnell: To be perfectly honest, it's about replacing failing light bulbs \$\endgroup\$
    – PPC
    Commented Oct 29, 2016 at 14:33
  • 1
    \$\begingroup\$ @PPC that's not clear at all from what was asked. \$\endgroup\$
    – scottbb
    Commented Oct 29, 2016 at 17:24

1 Answer 1


The electronic flash is designed around a hollow quartz bulb filled with a noble gas, usually xenon. This gas is normally a non-conductor of electricity. However, if a super high voltage is applied, the gas will ionize, conduct electric charge, and output a blitz of light akin to a bottled lighting flash. It takes 500 plus volts to do this deed.

A transformer circuit boosts low voltage from a battery or the household main to the needed high voltage. This high voltage is trickled into a storage device called a capacitor. The capacitor is akin to a bucket under a spigot. Even a trickle will eventually fill the bucket. Once filled, the bucket of water is available to be hurled onto a fire. The electronic flash’s capacitor is trickle-charged and once filled, is available to dump its charge into the flash tube.

The camera’s shutter circuit acts like a switch to signal the electronic flash to fire. The blitz happens almost instantaneously. Because the flash is a blitz of light to aim and adjust for effect, modeling light bulbs are installed in studio flash units. These are conventional low voltage light bulbs used to “model” (simulate) the action of the exposing blitz.

The photographer adjusts the intensity of the modeling lamps via a rheostat. Thus, the modeling bulbs are brightened or dimmed by adjusting the voltage applied. The modern studio flash contains a logic circuit that adjusts the output of the blitz to parallel the setting of the brightness of the modeling lights. This circuit adjusts the output of the blitz by altering the duration of the flash or the amount of charge applied to the flash tube or both. The modeling lights are quenched during the actual blitz. However they pale in intensity compared to the blitz so even if they remain on, their contribution to the flash is negligible.

  • 2
    \$\begingroup\$ Just me, but lose the first three paragraphs and you'd have a much stronger answer. And most dimmers these days use solid-state semiconductor switches to vary the voltage, not analog rheostats/variable resistors. You may also want to split out how the dimmer works from how the modeling/main light controls can be connected into a separate paragraph. As it is, though, you're seriously burying your lede under a ton of information the OP never asked about. \$\endgroup\$
    – inkista
    Commented Oct 28, 2016 at 18:35
  • \$\begingroup\$ @ inkista -- I believe that teaching encompasses making the story as interesting as possible. I think that dry facts often lose out compared to a more colorful explanation. The fact that a devise are superseded by modern solid state device is good information however, I don’t think this knowledge changes the meaning of my answer. Pushing 80, I am guilty of rambling. Let me add that I thank your advice and input. You are a valued resource. \$\endgroup\$ Commented Oct 28, 2016 at 19:08
  • \$\begingroup\$ @inkista Yso SORT OF just you :-) - No, not really, my engineer brain is happy with that BUT I'd probably put para 4 at the start as a summary and the others after it as detail. Satisfies both camps, more or less. \$\endgroup\$ Commented Oct 29, 2016 at 2:10
  • \$\begingroup\$ @Alan Marcus: I was indeed asking only for the specific modeling lights adjust through voltage control. You may want to emphasize the short answer before developing. Still, if the rest of the information doesn't benefit me, other people may find the resource very valuable. Thanks to both contributions \$\endgroup\$
    – PPC
    Commented Oct 29, 2016 at 14:32
  • \$\begingroup\$ @RussellMcMahon, that would've been my second alternative, but I felt I was already overflowing with editor dictates. :) The other problem, though, is that someone looking for how a flash's lamp/capacitor/charge cycle/IGBT works isn't going to look for that info in an answer to a question about modeling light control. \$\endgroup\$
    – inkista
    Commented Oct 29, 2016 at 17:54

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