Setting Up a Background Light
The background light is actually a fairly standard lighting tool for photography of all sorts when you are shooting a direct object or subject. A background light, in respect to the other lights, goes behind the subject and is pointed away from them and toward the background. This background light can have a lot of practical purposes in creating the image, and part of this is to make sure that the background has a relevant place in the image and so that the subject does not just blend in to the background somehow. This is why the background light is going to remain an important part of the light kit used in digital photography and part of how an image is composed. Here are a few tips and instructions for setting up a backlight for your photography.
Choosing to Use a Background Light
Using background lighting in your digital photography should be a must, at least on some level, when you are in a controlled studio setting. If you are outside and in a much less constructed location then you will not want to be carrying a huge light kit around with you, especially if you are looking for spontaneity. Beyond this, background lighting in digital photography is also heavily stylized and will not usually allow the object or scenario to appear as it would in real life. It can be used to sustain a realistic interpretation, but it is most often used in a multi-light set up that does not scream real world authenticity. You should check your situation first and see how the background appears, how the subject looks in front of it, and then whether or not you will need it illuminated.
Positioning the Backlight
The background light is often the fourth light in a four point lighting set up, which is similar to how it is used in digital video. What you need to try to do is to position the background light so that it is not able to be seen in the frame of the photo you are taking and so that it leaves the appropriate kind of light on the background. Oftentimes, you are going to want a soft light to lay onto the background so it will not remain obvious to the viewer of the photo. You should try to push it off to the same side as the backlight and then raise it up relatively high. You can then use a soft light diffusion device, a silk screen, or other ways of diffusing the overall light stream. If there is an object on the background, such as text, that you want the audience to see specifically then you can easily adjust the barn doors on the background light so that it will be seen as obvious.
Oftentimes background lighting in digital photography is used for a flat background, such as a wall. This is not the only type of background that could be used as many backgrounds are actually a little bit of open space or a series of objects. A background light can still be used here, but you just need to adjust it to fit your specific background more carefully. First, you need to make sure that there are enough objects for the light to hit, cause shadows off from, and to interact so that the background is more interesting. You should also see if you can create a sense of progressive elevation by putting small object closer to the subject and taller objects far away. You will raise up the background light even higher and spread it out over the background objects you are looking at.