Once a photographer decides to start using artificial lighting, they’ll soon discover that it is a wild creature that needs to be tamed. There are different ways to manipulate the light at your disposal; diffusing it, bouncing it, adding color to it, but one of the most useful options is controlling where it spills.
If you’re new to lighting in general or to this specific aspect of it, this short video, David Bergman with Adorama TV is a good primer for you. Here is a quick look at using grids to control your light.

Grids are light modification accessories that look like egg crates and restrict where your light falls. For instance, without it, a softbox will cast light onto your subject and your background as well. However, with a softbox, the light that hits your subject and background is greatly reduced.

No Grid

If all you have is one light, this may be useful because you’re getting as much as you can out of your light for that shot. But, if you want to isolate your subject a bit more or give yourself the freedom to light the background differently, a flash grid is incredibly useful.

[REWIND: Parabolic Reflectors & Umbrellas | What, Which, and Why To Use Them]

Also, if you aren’t using a softbox modifier but something else such as a Speedlite, using a grid is still an option for you. Two choices are the popular Magmod system and the ExploImaging Rogue 3-in-1 system.

Rogue 3-in-1 Starter Kit$39.95
Magmod Basic Kit$89.95

Along with your speed lights ability to zoom, you have a tremendous ability to control your light. If you are interested in more methods of controlling your light. Check the links below.

Headshot Photography Tips | The Gear You Need To Start Your Studio

The Sundisc Light Modifier | Aiming To Bring Studio Level Lighting To Your Pocket