Of all the ways to establish background, the kind of receding, almost disappearing background, one that is filled with tone without any detail, a high-key background offers the most in the way of creating extra-dimensional lighting without going to a great deal of trouble and excessive setup and testing. In order to create multi-dimensional lighting, that is to say, a hair light as well as modeling on a subject’s shoulders and back, you would need as many as three lights to get the job done. But with high-key backlighting, it is entirely possible to create that entire effect with only one light, none of which is entirely dependent upon the color of the subject in front of your camera.
The key to creating that surrounding glow behind a subject is to shine your back light through the background material and not on it. It does require a minor amount of special equipment, mostly in the way of a background material that is translucent. It is a technique that can be easily arranged with only two lights: the first, of course is your main light. For human subjects and a great many inanimate objects as well, the light modifier of choice is the softbox. In order to create the most flattering light on a human being there is nothing better than a large softbox for a soft and opulent quality to your strobe, particularly if there are multiple baffles in the box. One additional way to modify the light and create an even more congenial light, particularly on a subject’s face is to dress your primary light source with a 1/8 CTO filter for an additional bit of warmth on your subject’s face. This can be especially useful in winter when people’s skin tones are usually paler than in summer, and this holds true no matter what your subject’s skin color might be – everyone loses color in their skin tone in winter, even in sunny Southern California.
If you’re going to photograph people (and every photographer comes across portraiture sometime in their creative life), then a proper photo backdrop setup in a studio is an absolute essential, and there are a number of ways to go when purchasing one depending upon your budget. You may even already have one in your studio. If so, so much the better. But what is going to transform your lighting is the use of a background that will allow you to shine your backlight through it, a material that has some translucence to it, one that will allow a great deal of light to pass through while retaining it own integrity. Some will even take on the feel of frosted glass, but for our purposes it’s important to create a soft and bright light shining on your subject’s back that will create an almost angelic halo surrounding them.
What is critical in this setup is the balance of front to back light. Once you’ve established your exposure from your main light, you’ll want to meter the backlight from immediately behind your subject and proportion the light so that the backlight is at least one stop brighter than your main light, then gradually increasing or decreasing the intensity of your backlight higher or lower depending on how bright you want that surrounding light proportionally to your main light. The distance from your subject to the background will also play a large part in balancing the light. The closer your subject is to the backdrop, the less light you’re going to need. In such a setup, the backlight ought to be a bare flash tube. The vellum, or whatever material you’ve chosen as your translucent material, will act as a “rear softbox” as well.
This setup will work beautifully with a high-key subject, particularly if you’re photographing people with light or even white colored clothing, but it need not be necessarily so. With white on white, it is very easy to create such a great intensity of backlighting so much so that the edges of a white outfit can blend into the background and people with fair skin and hair will get slightly “blow out.” While shooting a total high-key portrait might yield some wonderful affects, people with darker skin or dark clothing under similar conditions will show a greater effect of too “hot” a backlight, creating an “overexposed” background and a pronounced halation effect, particularly at the more contrasty edges between your subject’s black clothing and/or hair and the bright white background, so make sure you keep the balance between your main light and background light as discreet and complimentary to each other as possible.