Light Source: The Illusion of Diffusion

Without diffusion, our movie talent would look old and rough, our shiny cars would reflect intense lights and our sets would fill up with hard splotches of light, with little blending. Without diffusion, our world would light up like a room with a bare light bulb hanging from the ceiling not a pretty sight. So how do you create the world you see on your television and in movie theaters, in which every actor has skin as smooth as silk and the cars all look like they came off the showroom floor? It is all part of the illusion of diffusion, the lighting designer’s greatest weapon against old age, rough skin and shiny objects. In this column we will look at the various types of diffusion available to videographers and describe many different setups for using diffusion.

What is Diffusion?

An advantage that you have when you are working with light is its tendency to travel in a straight line. Shine it on a reflector at an angle and it will bounce off at an exact complementary angle. While this characteristic of light is usually good, it does have a tendency to make light coming from an extremely bright bulb very hard. By hard, I mean that the shadow it casts has a very defined edge between the shadow and the light. This sharp edge is called the shadow edge transfer. This area of transition between the lit area and the shadow area defines whether a light is hard or soft. The sharper the edge between the two areas, the harder the light.


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Keep in mind, shadows are not a bad thing. They give your on-screen images a three-dimensional look. However, shadows also show the texture of a surface. If your talent is aging and has lines on his face, the shadows cast by the texture of the wrinkles will make his skin appear very rough and old. Any imperfections will be highlighted. While this is great if you are doing an interview with an old cowboy with lots of character in his face, your leading lady will not be too thrilled when the new wrinkle she found that morning is seen in all its glory due to your hard light setup.

Diffusion material takes a beam of light and spreads it out by bending the light beam through the diffusion material. The more dense the diffusion material, the wider the spread of light. The actress’s face would look years younger under diffused light because the light would spread more evenly over her face and not cast the shadow of her newly found wrinkle.

Let’s look at an example that you can see without setting up lights. If you walk outside on an overcast day, do you see your shadow? Probably not. The clouds act as a huge diffuser of the sun. As the clouds thin, you begin seeing soft shadows and as the clouds disappear, you will see well-defined shadows. You can easily duplicate this effect in the studio with a variety of diffusion materials and a little bit of practice.

Scrim Solutions

There are many tools you can use to diffuse light. The easiest and least time-consuming are scrims, gels and frosts.

A scrim is a wire mesh screening that is placed over the front of a light to reduce the intensity of the light and slightly diffuse it without changing its color temperature. These mesh screens can cover the entire light or, as half-scrims, cover only half of the light source. Scrims are very handy when you are trying to get two light intensities from one source. By placing a half-scrim on a light and rotating the scrim to the top, you can light your subject with the bright light from the bottom of the instrument and reduce the light on the background from the top half of the light. One word of caution: metal scrims get very hot, handle them with care.

Diffusing Gel

One of the most useful tools for light diffusion is the gel. There are more than 20 different types of gels you can use for diffusion. Gels are usually placed in five categories: frost, spun, diffused white, silk and grid cloth.

A frost is a soft diffusion gel that spreads the light beam evenly yet maintains a center and a defined light edge. It is ideal for spreading the beam of a light source while maintaining its characteristics. Frost gels are helpful when duplicating room lighting, such as lamplight. You will still get the round throw of what looks like the lamp’s light, but with get a softer shadow. Frosts comes in a variety of thicknesses so you can vary the effect to meet your needs.

Diffusion material, or "tough spun," is made of a heat-resistant material that looks like spun glass. You can drape it over the front of lighting instruments using a technique called "diapering." By clipping diffusion material over the front of a lighting instrument, you can spread the light’s beam without changing its shape, getting a more diffused but defined light source. Use tough spun on the front of an instrument to soften the light for younger actors who do not need as much diffusion to soften their looks. It is great material to work with because you can shape or drape it over anything. This material also comes in a variety of thicknesses.

Diffused white gels are thick, translucent gels that spread the light beam to create an even splash of light with no defined center or edge. These gels are ideal for creating soft shadowless light, much like that on a cloudy day.

Silk is a type of gel material that has a definite linear texture. Silk gels spread light in one direction, ideal for sending light across a set or specific object. Because it diffuses light in a particular direction, you can use it on several lights to eliminate the scallop effect created by spacing between the lights. Silk is also useful in controlling the light coming into the set at extreme angles.

Grid cloth is a diffusion material that has a built-in grid that creates a material strong enough to sew or grommet. This material is ideal for making lighting tents and butterflies.

Butterflies, Tenting and Softboxes

Attaching gels to the front of front of lighting instruments is the simplest way to diffuse light. There are however, a number of ways you can expand diffusion characteristics to light large or intricate settings.

A butterfly is a large diffusion tool that stretches over a solid frame. Directors usually suspend a butterfly over the object or subject they are taping and illuminate it with a number of lighting instruments hung above. Commercial directors use the butterfly to provide a large, even light over a shiny new automobile. They suspend the butterfly over the car and use the soft white reflection of the butterfly to give the car a three-dimensional look as well as make it look smooth and powerful. The light from the butterfly is almost shadowless, so it can evenly light an area and provide a soft, glowing ambience to the scene. Butterflies are also used outdoors (be careful, though they make great kites). If placed between the sun and your subject, you can use the sun’s light without having to deal its harsh shadows.

Tenting provides a soft, diffused light throughout the shot. You can drape grid-cloth like a tent over your subjects to surround them with a shadowless soft glow. This technique is often used to light objects for commercials.

A softbox is perhaps the most used diffusion tool in the industry. The softbox is a large box that fits on the front of the lighting instrument and diffuses the light in a very specific direction. It provides a great way to turn a 6-inch light with a very hard beam into a 24-inch light with a soft, diffused beam. This is ideal for people, because it softens and evens out skin tones. Directors also use softboxes when lighting shiny surfaces, so the reflected light sources aren’t just little spots of light.

Final Thoughts

Using diffusion is as simple as placing a gel in front of a light. However, you need to experiment with a variety of diffusion materials to learn what works best for your lighting situation. Remember that shadows are not bad, you just have to control them. With diffusion materials and techniques, you can control the amount and intensity of the shadows. By learning the ins and outs of diffusion, your talent will look younger and your products will sparkle.

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