Professional studio light sources generally go into one of these two categories: they get a kit with a flash head and a power pack, or they can get a monolight kit. A head and power pack kit consists of the flash head and a small power pack that acts as the generator that supplies energy to the flash head. The flash head contains flash tubes that emit light, once supplied with high voltages pack.
The two types of power packs are symmetric power packs and assymetric power packs, symmetric power packs split power equally between multiple flash heads. assymetric power packs allow the user to vary the power supply to different flash heads.
monolights are different because they’re a substitute for a power pack, or flash head combination. Their size limits their power, but they desired mostly for their portability, having all the controls on the power pack makes it easier to change the settings of multiple flash heads in one place quickly, monolights come with the controls built directly into the light itself. If you have multiple monolights, you’ll need to control and adjust the settings of each one separately. Head/power pack kits also offer faster flash times than monolights, which can really come in handy when you want to freeze action during fast motion. They also have faster recycle times,
if you’re shooting outside or with hard lighting arraignments, you’re going to need a lot of power to overcome the sun or the light loss caused by the modifiers. Head pack systems have a big advantage in the power department. But if you’re shooting inside a building or inside a studio, monolights will probably suit the job more.