When it comes to expanding your lighting gear in order to start taking more professional, high-end studio photographs, you will initially be faced with a choice between flash guns and studio lights. The truth is there is no right or wrong, good or bad when it comes to lighting equipment. It all depends on your particular needs, as well as your budget along with many other factors that are specific to your kind of work.
Here, I will try to cover some of the most important factors, and provide a comparison between both options to hopefully help you make an informed decision as to which of these two is the right thing for you. Let's note up front that flash guns are also known as speedlights and hot shoe shoes flashes. They are small battery powered units that can be used attached or unattached to the camera.
Studio light or strobes come as moonlights or pack-and-head lights. They are larger, more powerful, and operate away from the camera. They usually need to be plugged into a power source.
Through-the-Lens vs. Manual Metering
Through-the-lens metering, which is also known as TTL metering, can be used with flash guns to help the photographer make informed decisions when shooting whether the speedlight is mounted on the hotshoe of the camera or set somewhere off camera on a stand.
In TTL metering, the flash actually emits a light prior to the actual flash firing that is used for registering the exposure. This first light is known as the pre-flash. It then measures the amount of light that is returned through the lens and compares it with the original amount of light emitted, taking into account the distance between the camera and the photographed subject.
Based on those facts, it then calculates the power the flash needs to be set at in order to register an appropriate exposure (a correct exposure).
With studio lights (studio strobes) you need to work with manual metering as they don't provide the luxury of TTL metering. This means that you basically need to use a handheld light meter to be able to tell what settings need to be on the camera as well as the power and settings of the strobe. Or you have to use trial and error and the LCD on your camera to do it. Once you do that, you then set your camera and lights according to your readings and shoot in full manual mode.
If you're doing a lot of on-location photo shoots, outdoor portraits, events and weddings and even documentary work, a flash gun will probably be your best bet. Flash guns are small, light, they run on batteries and they can easily fit anywhere you store them.
Studio lights on the other hand can be bulky and difficult to manipulate in tight spaces. They are large and require special attention so they don't break while being handled and moved from location to location.
In addition to that, some studio strobes come with power packs that they operate in conjunction with and they need an electrical outlet to be turned on (though some do actually work on batteries as well), which is something that may or may not be available where your photo shoot is taking place.
In terms of light power that can be obtained from your light source, studio strobes are far more powerful and intense than regular flash guns. This also gives some creative flexibility to your shooting by allowing you to attach all sorts of light modifiers and bounce light off of walls and ceilings, even in larger and more open spaces. Flash guns are usually used in tighter spaces where light loss isn't that huge due to their lower power and intensity.
Non-continuous light sources need time between consecutive firings to regain energy and be ready to fire again. Recycle time is how long it takes the light before it is ready to fire the next blast of light. In that regards, studio strobes definitely refresh faster and thus allow you to shoot faster than portable flash guns.
A flash gun might may need up to six seconds to recycle after a full power burst. While studio strobes generally pull in more power and can recycle after a full power burst in less than a second. They also contain fans, so they cool down quickly and can take faster shooting rates.
Because studio strobes are more powerful, you can get more light of them in a shorter duration. While all strobes and flash guns may seem to discharge their light, well, in a "flash," some flashes are longer than other. If you're hoping to freeze action, powerful short durations are good. In this sense, studio strobes have the advantage.
But many flashguns are now equipped with high speed sync, which lowers the power of the flash in order to squeeze it's flash duration into a faster shutter speed. The allows you to use a faster shutter speed to freeze action.
So, we can call this one a draw. If you need to freeze action and be mobile, go with a flashgun. If you need more power, studio lights are the winner.
In terms of creativity in the area of light modification, strobe lights definitely give you more room for different settings and mounting of a variety of light modifiers such as softboxes, umbrellas, flags, snoots, reflectors, honeycombs, barn doors and many more.
Of course with flashguns you can do some sort of light modification like attaching a diffuser to your speedlight, but there are not nearly as many accessories to experiment with. All in all, to have more room for creativity, freedom and mixing and matching of lights and modifiers, studio strobes are definitely the way to go.
In terms of consistency from one exposure to the next, both in power and color temperature of the light, studio strobes are generally much more consistent than flash guns. The reason for that is speedlights are operated on batteries while studio strobes usually connect to an electrical outlet where the power is quite stable. With batteries however, the more power you consume, the lower your battery gets and that's when your light starts to become weaker and color temperature starts to vary.
Strobe lights generally come with a built-in continuous modeling light which allows you to see how the lights and shadows fall on your subject prior to making the shot, so that you get an idea of how your picture would look and have the opportunity to fix and adjust your setting before you start shooting.
Continuous modeling light can also come in handy in poor lighting conditions allowing you to better see and place your subject as well as easy pre-focusing. Flash guns on the other hand normally don't give you the flexibility of previewing your settings, pre-focusing and clearly seeing your model in low light conditions as the vast majority doesn't come with a continuous light option.
Comparison between speedlights and studio strobes is not a very logical approach sometimes, because each has its own advantages and disadvantages over the other in some specific areas, and each was built to serve a particular purpose. It all boils down to the work you normally would use them for.
If you are just starting out and need something to put you on track, especially if you might be photographing your subject outdoors or documenting events, generally you might make better use of one speedlight or two.
If however you're looking to specialize in using the controlled studio environment, whether portrait or fashion or product photography, indoors or even outside then I would suppose you are going to need to go with the studio strobes route.
Here are a couple links, one for best-selling flash guns and the other for best-selling studio strobes according to Amazon. Hopefully these might help get you started: