Hard light refers to light that comes from a relatively small source--or a large source that is far away from the subject, like the sun. Light radiates from this small source and casts hard-edged shadows and creates tiny, tight highlights. Soft light comes from a larger source--or one that is physically closer to the subject and therefore appears larger. Soft light casts vague, soft-edged shadows and creates large, sprawling highlights (Figure 1).

Figure 1. Note the difference in the hard light (left) and soft light (right) as key. The shadow of the nose and the shadow of the chin are markedly different.

Soft light is the "in" look right now for many lighting situations, particularly interviews and close-ups. There's a good reason for this: Soft light is very forgiving. It's easy to set up a soft light and create a nice look. The light is also flattering to subjects, ironing out tiny wrinkles and skin blemishes that might be accentuated by hard light. Soft shadows don't require the careful placement needed for a pleasing look with hard light--they look pretty nice wherever they fall. As a result, many camera folks have nearly abandoned hard light for Chimeras and Kino-Flos. Although this is fine for certain situations, you shouldn't do it in every situation.

Let's take a look at how soft light works. Soft light can come from bouncing hard light off a large white surface (like a ceiling or wall) or by shining it through some type of diffusion material, such as a soft bank (Chimera, Photoflex, and others are name brands of the generic soft bank). In these cases, the light becomes soft through two mechanisms: one, the light is diffused, which means the beams are randomized or scattered; two, the light source itself is physically large. A white wall may be 8 feet high and 10 feet wide. A soft bank may be 3 feet square. Because the soft bank is placed close to the subject, the apparent size of the light source is very large. The large size of the light source helps create the softness of the shadows, but it also creates another effect called "wrap," which is exactly what it sounds like--the light wraps around the subject.

Wrap occurs because the large diffusion fabric on the front of the soft bank is throwing light at the subject from all portions of its area, thus from different angles. The light emanating from one corner will hit the subject from a different angle than the light emanating from the opposite corner (Figure 2). The apparent effect is that the light wraps around curves. Hard light, on the other hand, is pretty much straight on: It hits one side of the subject, throws a shadow, no wrap.

Figure 2. A soft light transmits light from all portions of its area so the light arrives at the subject from a variety of angles. This creates the wrap that allows the light to curve around surfaces.

In essence, it's useful to think of the soft bank's surface as a large array of tiny hard lights. And, in fact, if you took a 3-foot square of plywood and mounted a hundred small bulbs over its entire surface, you'd have a source that creates a very similar look to a soft bank of the same physical size. In fact, some 3D animation programs use this technique to create soft light sources.

Because the apparent physical size of the source plays a huge role in how soft the light seems, soft lights are best used fairly close to the subject. But that's not the only reason they are typically used in close proximity. The other reason is that they are inefficient at any distance and gradually lose the "soft" advantage the farther they get from the subject. Soft light simply doesn't throw far.

There's another use for soft light, and that is as wide-area fill. Often, I'll bounce a 1K off a white wall as fill, or fire a bank of Tota-Lites through a butterfly, a large frame with diffusion fabric stretched across it. When it's time to improvise in the field, a white bed sheet might become the diffusion, or the time-tested cheap frosted shower curtain.

From a functional viewpoint, it's clear you need to use hard light as a key whenever you have to throw the light any distance, and you can use a soft source when you can move the light in close to the subject. But, of course, in the latter case, the actual decision is an artistic or aesthetic one, not a functional one. You may still choose to use a hard light as key even when you could get in close enough to use a soft light.

Another thing to keep in mind is that this is not an either-or decision, but sometimes a both-and option. When lighting a set, you may need the principal sources to be hard lights to reach across the required area. However, when you move the camera in for a close-up, the lighting must be optimized for the face, not for the entire room. That's when you might bring in a soft bank to punch up the lighting on the face, even though in a master shot of the whole set, the subject's face is lighted by hard light.

One of the neatest implementations of this technique, and one I heartily recommend for dramatic scenes, is the use of a China ball on a fish pole. Whether the China ball is an old-fashioned white paper ball with a photoflood bulb inside or a fancy pro version made of spring steel and diffusion fabric, the effect is the same. When the camera moves in for a close-up, a grip with the China ball on a stick runs in and places the soft light source close to the actor's face to punch up highlights. This creates nice eye lights and generally optimizes the lighting for the close-up. When the camera turns to another actor for a close-up, the same grip brings the China ball in for the shot. Easy, fast, efficient. I've heard the technique was developed on the set of NYPD Blue and has been a staple of the show's shooting style ever since.