Most modeling lights allow lighting with variable intensity. What technology do they use for that?
Is it voltage reduction, some kind of AC throttling?
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.