Light Diffusers and Gels

Applications

The number of materials that can be used for light diffusion, reflection, or modification is bounded only by your creativity and imagination. Once you start looking, you will find items everywhere that can reflect and diffuse light in unique ways. Whenever you find an interesting material, you should try to take a picture of the effect it creates. Keep a scrapbook of these effects for later use. You’ll find that you can look through this book before a shoot begins and you will instantly recognize particular scenes or shots that could be enhanced by using one.

The point of using any of these materials with light is to change the light with a particular goal in mind. This goal may be as simple as casting a cool pattern on the back wall or may change the color of the light, so the scene will photograph correctly. Try to experiment extensively with all materials you planned to use as many can have unexpected consequences on your final image.

General Instructions

Modifying light is more of an art than a science. You have to subjectively determine the results that you want to achieve. Deciding on the plan to achieve the look you desire can comes from planning and logical thinking. One of the most important steps to methodically creating a lighting scenario you’ve devised comes from studying how light actually works and what modifications actually affect the final image on your medium.

Color temperature

All light contains a range of frequencies. For film, these frequencies are denoted as temperatures which are measured in terms of kelvin (K). In table 28-1 you can see a list of common light sources and their temperatures. Our eyes automatically adjust to these color ranges. Film and video, however, don’t adjust easily and have far more limited ranges than our eyes. For this reason, every filmmaker must understand how the color temperature will affect the final image you capture – whether on film or video.

To understand how to effectively use light in your film, you need to know that most light, film, and video settings are divided into two main categories. The two main guideline temperatures of light you need to know are:

3200 K for artificial light

5600 K for daylight

TABLE 28.1 Color temperature in kelvin.

If you use daylight-balanced film or the daylight settings (for white balance) in your digital camera, you are attempting to photograph in the daylight temperature range. If you are using tungsten-balanced film or the indoor settings in your digital camera, you are attempting to photograph in the artificial light temperature range. Daylight temperature in the color spectrum tends to be bluer. Artificial light tends toward yellow/red/orange.

What happens if you use daylight settings to photograph artificial light? In a room with a window with daylight coming through and a single lamp, all of the objects lit by the daylight will look normal, while items on which the lamp shines will look extra red/orange. Likewise, if set for tungsten settings, the lamp items will look perfectly fine. Any objects outside the window or those lit by daylight will appear almost a monotone shade of blue.

Why is light temperature important to you? One of the primary uses of gels is not to change the visible color of light, but instead to change the light temperature. Blue gels (CTB) can be placed over a tungsten light and filter out all the color temperatures but those within the daylight range. That can allow you to use tungsten lights to augment daylight scenes without adding an orange cast. Likewise, orange gels (CTO) can be used to filter daylight so that it shows through only in the tungsten color temperature range.

Therefore, whenever you use any type of colored gel or diffusion, be aware that it may have an unexpected effect unless you take into account the color temperature range of both the light source and the setting for your recording medium.

Color temperatures can be determined with the help of a color temperature meter (see figure 28-1). These meters can take a temperature reading from a light source and even suggest what type of gel or filter would be needed to bring that source into the desired temperature range.

Traditional diffusion

Diffusion is used for a variety of reasons. Perhaps the light needs to be softened. Maybe the actress needs a warm glow on her face. It is up to the skills of the DP to choose the right diffusion to achieve the lighting effect that is desired for the scene.

FIGURE 28.1 The temperature of a light source can be determined with a color temperature meter.

Realize that reflectors, diffusion, and other light-modifying materials all cut the amount of light that hits the subject. Therefore, a light source that may be bright enough when uncovered may be too dark once diffused or reflected. For example, lights with lenses (such as Fresnel lights) can project up to 50% less light than an equivalent light without a lens. Always take into account light loss when setting up a diffusion or reflective light scheme.

Almost anything can be used as diffusion material. Guerilla and professional filmmakers regularly use household items. Some household diffusion materials include:

•  Sheet A normal bed sheet can be used as a white reflector or a fairly dense diffusion material. Simply hanging a white sheet opposite a well-lit window can change the entire light feel of a room. Watch for white sales and discount coupons to purchase sheets inexpensively.

•  Window sheers The translucent material called sheers that is often placed behind curtains provides excellent diffusion. It is available in a variety of white and off-white colors and may be purchased in silk or polyester varieties. If your city has a garment district, this material can be obtained inexpensively. Generally try to purchase silk sheers as the polyester sheers reflect a good deal of light and as such make poorer diffusion material.

•  Silk blouse Often old silk blouses provide excellent diffusion and can be found cheaply at thrift and used clothing stores. You may need to sew several together to cover the entire frame.

•  Satin sheets Available in white and other colors, satin sheets provide excellent soft light reflection.

•  Tracing paper for diffusion Warning! Tracing paper, like all papers, is very flammable. Although tracing paper is regularly used for diffusion in professional sets, it is commonly used to cover an outside window when the lighting is either supplied by the sun or with a distantly located powerful light. Make sure you don’t place your light source close to this paper.

•  Aluminum/tin foil Fix aluminum or tin foil to cardboard or foamcore. I find the easiest way to attach the foil to the board is to staple it directly to the cardboard.

•  Mylar Mylar is a fantastic material for lightweight yet extremely reflective applications. The major drawback with Mylar is the expensive price. Watch for it on sale at local party stores.

•  Colored cellophane Typically available at party stores, colored cellophane is available in a variety of colors for various light effects. While you can’t effectively use colored cellophane as a gel (such as CTB or CTO) it can be used for general mood coloring of light.

•  Window tinting Window tinting material is available at home improvement stores as well as automotive supply stores. At the home improvement stores, you can find a variety of levels of tinted material that is meant to be stuck to a household window with static cling. I found this material to be cheap and perfect as a diffusion or scrim-like material. Be aware that it is generally shiny and may create a reflection of other lights.

•  Window screen You can buy this screen material without the frame at a hardware store. It’s perfect to cut to size and use as a large scrim.

•  White or black trash bags Can be cut open and attached together to create a nice shiny plastic reflector similar to a professional griff (or griffolyn). Most often you’ll use this as a bounce material to create fill light.

•  White or black foamcore Foamcore is probably one of the most used materials in the film industry. It provides excellent backing material for another material. Foam core is often used with the white side for a reflector or the black side as a flag. It can also be easily painted for a simple backdrop or a blue screen background. Generally available in 4′ × 8′ sheets.

•  Foam insulation board Although they’re flammable, so they’re only really suitable to reflect sunlight, foam insulation panels are extremely cheap, available in large and small sizes, and provide effective reflectors. Available at almost any hardware store, these panels are made of lightweight rigid foam with one side white and the other side dull silver. I use these all the time.

•  White van or truck More than once have I seen this trick used to great effect. Placing the large white side of a truck or a van at the proper location can provide an excellent bounce surface for fill light. It can also increase privacy to minimize spectators.

•  Acrylic light panels Available at any hardware store, acrylic light panels made for fluorescent light fixture can be obtained cheaply and provide a wide variety of diffusion types.

•  Chrome spray paint Available at any auto parts store and most hardware stores, chrome paint can be used to create an excellent reflective surface on nearly anything. Generally also available in gold color.

Special effects diffusion and reflection

Special effects diffusion and reflection is much more difficult to use properly. Not only does the effect look excessive if not used cleverly, but many lighting effects break the light into patterns. These patterns are difficult to control and may fall unattractively on the face of an actor or actress.

Here are some examples that I have seen used effectively on sets:

•  Tape on frame to simulate window slats A simple cross design on a frame can provide an excellent simulated window if used in front of a light source and cast onto a white wall.

•  Bicycle tire to simulate television Attach strips of blue clothe or gel on a bicycle tire. Placing a light source behind the tire and then turning the tire can cast a flickering reflection onto an actor’s face. Use this technique with orange or red gel strips and fire may be simulated.

•  Stained glass Using a variety of cellophane, you can effectively simulate the light patterns of stained glass windows. I saw this used to simulate such a window on the back wall of a “nunnery” and I was stunned by the final footage. What was a bland little room became an expensive holy room using this simple effect.

•  Kaleidoscope A few of these toy kaleidoscopes and a number of spotlight bulbs can be used together to create an interesting psychedelic/rave party environment.

•  Matching color light This technique can create fantastic results, but I’ve only seen it used a couple of times. Take a surface such as a red wall and place a red gel over the light shining on the wall. The light will supersaturate the color of the wall for magnificent effect. Used carefully, the same technique can even be used for smaller surfaces (i.e. use a red gel on a light hitting a red dress).

•  Rope weave cookie A rope weave can create a fantastic, natural-looking, and portable cookie.

•  Aluminum/tin foil with cutouts Cutouts in aluminum foil can create interesting reflective effects including simulating broken glass reflected onto an actor’s face.

Suggestions

Here are a few suggestions to help you with light modification:

•  Be frugal with your lighting effects Setting up a light effect properly can take a great deal of time and using too many effects in one film can make it look cheesy. Be reserved in the effects you use to achieve the greatest dramatic impact when they are seen.

•  Match your mediums If you are using a digital camera for your film, use a digital still camera for your tests. Likewise, if you’re going to use film to record your movie, use a real film camera to perform any light tests. Digital encoding and film exposure record images in very different ways. It is important that all the lessons learned from your experiments will correctly translate to your final medium.