I have been working with and writing about strobes for several decades. In that time I’ve made a really huge number of images with strobes. All strobes have certain characteristics: they have a daylight spectrum, and the light has very short duration. These characteristics make them the best lights for still photography, because you can mix strobes with daylight and also stop action.
Several characteristics are really important in understanding how useful any particular strobe might be. First, know how much light output the unit has. Second, know the coverage of the strobe, how big an angle it illuminates and how evenly. Third, does the unit have a modeling light? These continuous lights on a strobe make it easier to see what the strobe will do. Fourth, how quickly does it recycle, that is how soon is it ready to shoot again? Fifth, how portable is the unit? Finally, how easy is it to control the unit: will the strobe work with your camera’s automation?
How powerful does a strobe need to be? That depends on several factors, including the way you use light and the ISO you shoot at. I really like using big light sources to create soft light. Such light sources are not very efficient; so much of the light the strobe puts out won’t end up on the subject. In Figure 1, I used a light panel and an umbrella to make a big light source on the left of the camera. If I had used the strobe directly on the subject, the aperture would have been f/22.2 at ISO 100, but because of the light modifiers, the aperture was f/8.7. So I lost more than 75% of the light I started with. Consequently, I need strobes with a lot of power. If I had used a more efficient lighting design, I wouldn’t have used as much power, but the light wouldn’t have had the same quality. Large light sources illuminate the subject from more angles, making softer light with more gradual transitions. I used a second light with a beauty dish to give the subject more definition and a good catch light in the eyes.