Flash units can be run from an in-built battery or from the mains electricity. Generally the smaller flash units that fit on cameras and flashes made by camera manufacturers are battery operated, while most flashes designed for use in larger photographic studios run off the mains. There are a few exceptions to this, and a few in-between models, including mains units that run from power packs.
Some people use mains flash units because some are available cheaper, some because they want more power than is available from battery units and some because they are looking to have access to more attachments.
Flash has been traditionally used instead of continuous lighting because there was a lot of heat produced from light that was anywhere near as bright as a flash, and it was difficult to mix light sources Today with Cool Lites neither is true in many cases, but as many photographers want a single light source, they have tended to stick with flash, while it may be that they would benefit from using both.
I currently have all 4 sources of lighting, tungsten - rarely used now, cool-lites, mains flash and a Nikon Creative Lighting system.
In this article we are concentrating on the mains based studio flash equipment, the other options are covered in other articles in the Lighting and Reflectors Section.
There are quite a few companies producing mains flash units, and although they range in price considerably, you can get a mains flash for far less than a flash by a camera manufacturer.
Lets look at an example. Lastolite offer a kit designed for professional use that contains, 2 mains flash units (lumen 8) that also have modelling lamps, 2 Ezybox soft boxes, 2 reflectors, 2 stands, a sync lead, and a wheeled case for the kit, all for £450. While a Nikon SB900 on its own, in the same catalogue was priced at £324.50, and a Lastolite Ezybox Hotshoe kit with stand is £176, so making the equivalent kit, with two stands, softboxes etc would cost over £1,000 based on the SB900. As cheaper kits than the Lastolite is available, you can see why many photographers, when setting up studios, are attracted to mains flash. Interfit had a 2 head kit with stands, soft box etc at a recent show offered at £199. Like with many other things you can also find makes that allow you to invest more, should you choose to, often with more complex systems, perhaps offering more options.
The component parts that make up a flash system are covered in the article Studio Lighting - The Parts.
With flash we have a number of factors to consider:-
When using flash you may be interested in how long the actual flash lasts, but this is rarely important. You may need to know the colour of the light, particularly if mixing it with other light sources.
How the attachments or component parts fit on is perhaps a consideration that should be considered more than it is, some systems are quick and easy to use, others more ideal for when charging your time by the hour.
Quality is often associated with weight, the larger and heavier units being a better quality build. However if you have to move this about from place to place then selecting a lighter system that is easier to move may be more of a priority.
Physical size and how much it can be folded down as well as carry cases may also be important if you need to take your lighting with you.
Storage should also be considered, often lighting systems can be quite bulky, which is fine if you have plenty of spare rooms, but if you don't or have to rent space then you may find you are resulting to hiring storage just for lighting and similar items.
With mains flash, we cannot control the power of the flash from our camera, and the flash and camera do not work together as it would in a manufacturers system, like the Nikon Creative Lighting, so we normally run our cameras in manual exposure mode when using mains flash.
The only specific piece of information we need is at what aperture to set for the given ISO. We could deduce this by a combination of calculations, guesswork and trial and error quite quickly using our camera curve and preview images to confirm what we have got. The calculating part comes from using the Flash Guide Numbers.
Most of us however cut through this process by having a flash meter, this can be a low cost, simple device that you set to look out for flash, then tiger the flash, and it measures how bright the flash was. Using scales on it you can then deduce the aperture for a given ISO.
You can adjust the power of the flash on some units, while with others it's a case of moving them back or forwards to vary the strength.
Example Equipment Items - based on a low cost Portaflash System
There are many articles on flash, lighting and reflectors in the Lighting and Reflectors Section.