Studio Flash Power Packs

 flash power pack

 Still the powerhouse of professional studio lighting, the flash power pack offers exceptional flexibility, operation conveniences and reliable repeatability. Faster recycling, radio frequency triggering and digital power displays are among the desirable features of the latest generation equipment.

While the ability to control colour temperature with digital capture has given continuous lighting a new lease of life in the studio —as has the arrival of LED-type sources from the pro video world —the flash power pack still provides the most flexible lighting solutions for studio-based photography. And the availability of battery-powered options for some systems extends this flexibility to outside locations.

The basic configuration of the studio flash power pack —also often known as floor packs or flash generators —remains pretty much unchanged from the original units which were devised in the 1950s. The power pack  centralises  the flash power supply and control circuitry in one component which has a number of outlets, typically between two and four for connecting flash heads. Broncolor s adoption of electrolytic capacitors in 1962 allowed for more compact units —they no longer needed wheels! Subsequent developments have concentrated on further improving the portability and enabling more precise control of the flash output and its colour balance. The adoption of microprocessors to control flash pack operations has allowed for functions such as programmed delays (for strobe sequences), sequences and multiple flashes. Importantly too, settings can be stored when the pack is switched off. Modern electronics have also greatly increased the safety of studio flash equipment. The flash head connectors are monitored so that, for example, no power is delivered to an outlet if the plug is not correctly seated or there is a problem with the head itself. The old days of studio flash equipment going bang in a spectacular way are thankfully past.

Digital displays are another benefit of using microprocessors to control a flash power pack s functions, although these read-outs are only really helpful if they correspond —in both values and increments —to accepted methods of exposure control and can be easily related to these methods when making adjustments. Today the majority of flash power packs provide digital displays which allow the power settings of each head to be read at a glance and, in operational terms, there is the advantage of having sequences such as recycling completed in unison and indicated by a single confirmation signal (audible and/or visual).

Full-logic control also permits full remote operation of a power pack and a number of top-end models have multichannel capabilities so that two or more can be used in a lighting set-up. Apart from the convenience factor, remote control allows the packs to be off the floor (on a rail system, for example) to free up working space in the studio.

Aside from determining your flash power requirements (based on the likely applications), the key considerations when selecting a flash power pack are the method of power distribution, the output range, flash durations and recycle times, power supply regulation and the triggering options available. The system s flash head design may also be critical to some applications.

A large number of the power packs currently available offer the choice of symmetric or asymmetric power distribution, and all have variable power outputs. At the budget end of the market this may be over just a couple of stops, but the better-featured models offer an output range of up to eight, nine or ten stops with adjustments at least as fine as 1/10-stop increments. Asymmetric distribution divides the power output unequally between the flash heads either by fixed levels determined by the number of heads and outlets used (for example, 67:33 or 67:16:16), or by ratio controls which allow the output of each flash head to be independently varied. Fully independent asymmetric power control enables precise adjustment of lighting ratios to suit the application.

Some flash power packs are specifically designed for high-speed applications —such as fashion photography —which is achieved via a shorter flash duration and faster recycling. There is a fundamental relationship between flash power and flash duration —basically, more of the former increases the latter —but there are various methods of enabling shorter flash durations such as using fewer higher voltage capacitors and shorter flash tubes. However, at higher flash power settings it will still be a challenge to keep up with the 10 fps continuous shooting speed of the latest pro-level D-SLRs.

 flash power pack

Some shifts in colour balance will be encountered when using lower power settings as the intensity fall-off curve —which is when a decrease in colour temperature occurs —becomes shallower and represents a larger component of the total output. Many of the latest generation packs can electronically regulate for this, minimising the shift, but obviously digital capture also provides control over the colour balance —either in-camera or post-camera —so this is no longer as much as a problem as it was when using colour film.

Once essentially just a metal box with a set of outlets and electromechanical switches, modern studio flash packs boast attractive styling and colour schemes, high-tech construction materials and well-organised control panels with backlit keys and digital displays. These units are designed to compliment the contemporary studio space, but functionality should still be the key priority when selecting a piece of imaging equipment that needs to work for its living.

Reading The Numbers


The maximum power output is stated in joules (J), but in the literature from some manufacturers you will find references to watt-seconds (Ws). The two units are equal in value, but it should be noted that in either case this measurement only refers to the power supply and does not denote the light output. There are many other factors which affect the real light output (the efficiency of the internal circuitry, the flash tube, the reflector s design, etc) so it does not necessarily follow that two floorpacks with the same power capacity will produce exactly the same amount of light.


The guide numbers used in this directory are those quoted by the manufacturers and refer to a flash head fitted with a standard dish-type reflector (which usually has an angle of distribution between 50 and 70 degrees). It is generally measured at two metres from the light source and refers to a sensitivity setting (or film speed) of ISO 100. If the measuring conditions are different from these, the variation is noted in the entry. Some manufacturers quote an f-stop in which case you can apply the formula GN = f-stop x distance (i.e. the light to subject distance). To work out the aperture, the formula is f-stop = GN/distance.

 flash head


Flash durations are based on the t=0.5 measurement, as defined by the International Standards Organisation (ISO). This refers to the length of time at which the light output is over half its maximum value. In some instances the effective duration may actually be longer (although modern control circuitry and components —faster discharging capacitors, for example —are improving the accuracy of this measurement), so some manufacturers also quote the more conservative t=0.1 which refers to the duration at which the light output is at least ten percent of the maximum power. Unless stated otherwise, the flash duration quoted refers to when a single head is fitted.


The quoted recycle times refer to when recharging to the pack s full power output and when drawing from a 220-240 volt (50 Hz) mains supply. These times will be shorter at lower power settings. Some packs can be optionally  turbo-charged  to speed up recycling. Most models offer a choice of recharging speeds and the slower rates reduce the amount of current drawn from the mains power supply. If a number of packs with rapid recharging are all connected to one power line, overloading may result which will cause the circuit s fuses to blow.


The maximum power modelling lamp permitted is quoted per head connector and not the power pack. Multiply by the number of head outlets to arrive at the maximum power permissible per unit.


Prices are quoted with ten percent GST included. However, this can be claimed as a tax input for business-related expenses. Unless stated otherwise, the quoted price refers to a single flash power pack supplied without any lamp heads or accessories other than power and possibly sync leads.

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