Backlight is a versatile light with great potential.
The term backlight refers to the use of a light which is projected from the back of the scene/studio onto the subject from behind. The camera is placed facing the subject. It captures the effect of the light as a highlighted rim or halo around the back edges of the subject.
The use of a backlight creates very distinct effects. The most important is the rim light around the edges of the subject. This highlighting effectively isolates the subject from the background. So it is a useful technique when the subject and background share similar colours or tones. The rim effect around the edges of the subject is especially useful for bringing out highlights and style in hair. Sometimes it is also used to imply purity or goodness after the manner of a religious halo.
Backlight can be produced either with artificial light, natural light or a combination. The sun is normally the most important light for back lighting and so in cases where sunlight is strong artificial light is often used to bring the foreground or the subjects front side out of shadow. This is fill light and provides sufficient light for a good shot of the subject without blowing out the effects of the back light.
In photographic scenes the backlight is often used to create an emphasis on the three dimensionality of the subject. Lights coming directly from the position of the camera tend to make a subject look flat because all the shadows are removed. Backlight has the opposite effect. The light halo effect at the back of the subject emphasises the depth of the subject. It can also be used to emphasis depth in the picture. By strongly highlighting the back of the subject the distance to the scenery behind the subject is revealed giving the image some depth.
Setting up an effective backlight requires some care. If the source of the light shines directly into the camera lens it will blow out and create a strong distraction for the picture viewer. Also a strong backlight can make the front side of the subject look very dark or even silhouetted. To prevent this it is normal practice to use a front light as well so the subject is bright enough to capture. Setting up a good backlight often requires getting the foreground light correct first, then putting in the backlight at around 2 to 3 stops brighter to create the emphasis.
The angle at which a backlight hits the subject can be critical. If the backlight is directly toward the camera the subject can be strongly blown out by and direct light passing around the subject. Normally backlight is applied at an angle. That way the lighting will provide a little texture on the subject and not be directed into the camera lens. It can also be used to more effectively show fashion elements like hair styles by picking out highlights, curls etc.
“Backlight” should not be confused with background lighting. The latter is where a light is used to light the background, the scenery or backdrop. Background lighting typically faces away from the camera. Backlights face toward the camera.
Backlights are used in such a large variety of ways that some practice and experimentation is needed to be able to work out the best way to use them. However, because of the intensity of the light from the back the foreground lighting is often important too. It is not unusual for multiple artificial lights to be needed in order to get the best out of backlights and to keep the balance of lighting good all around the subject.
Backlight techniques are very important in photography as they have so many effective outcomes. It is certainly worth practising with your lights or even natural light to try out some of the effects.