Light Source: Color Correcting with Gels


Have you ever looked at your video after you returned from what seemed to be a perfect shoot, only to find your footage is blue and you can’t really see the city skyline as well as you thought? Or what about that beautiful wedding shot in the ski chalet that turned out really orange? One of the most frustrating aspects of doing on-location shooting is dealing with multiple light sources. You may be sure you white-balanced the camera, but the deadly mix of different lights, spoils the shot.

Anytime you find yourself mixing outdoor light with indoor light or fluorescent with incandescent you run into problems. In this column, we will look at light from a standpoint of color temperature. We will discuss the gels that you can use to change the color temperature of the light so that you can use multiple sources.


Color Temperature

Your eye is an amazing organ. When you look at a white T-shirt outdoors, it looks white. In an office lit with fluorescent tubes, it still looks white. Even in your living room at night, it looks white. While this might not seem so amazing, it would if your eyes worked like a video camera.

When a camcorder set for use indoors sees the T-shirt outdoors, it looks light blue. In an office the T-shirt will look light green. If you set your camcorder for outdoors and videotape the T-shirt under normal living room light, it will look orange. This occurs because different color temperatures exist in all three areas.

Your eye compensates for the changes in color temperature so quickly that you don’t notice the shift. The video camera doesn’t have that ability. You have to white balance your camcorder under the light source in which you are shooting in order for your video camera to see white as white. What you are really doing is adjusting the electronics in your camcorder so that it can see the proper combinations of red and blue in relationship with green. The video camera sees white, under a given lighting situation, with the proper combination of these three colors.

When you adjust the white balance setting on your camcorder for indoors or outdoors, you are adjusting the color temperature controls of the video camera. The various color temperatures are expressed in degrees Kelvin(K), the scientific temperature scale. Outdoor light, usually referred to as daylight, ranges from 4500K to 6200K with the average being 5600K. However, on clear blue days, the color temperature could be as high as 12,000K. Indoor lighting, such as incandescent light, usually lies in the 2800K to 3400K range with the average being 3200K. Office fluorescent lights range between 4000K and 7000K with the average being 4300K. By knowing the color temperatures of the light you are using, you can take the next step in controlling the color temperature of your lighting configuration.


Color Correction Gels

One of the most useful tools available to the videographer is the color correction gel. This is translucent pliable material that you can place in front of lighting instruments, or on windows, to change the color temperature of the light source so that it matches the primary light source. You can use specific colors to change indoor or incandescent to daylight, daylight to indoor, incandescent to fluorescent and vice versa.

If you find yourself shooting in a large office with big windows, your best bet might be to change your indoor lights to daylight. You can do this by placing blue gels, often called CTBs, short for color temperature blue, on the front of your lights. The CTBs will change the color temperature of your lights from 3200K to 5600K, simulating daylight.

For those situations when light from a smaller window mixes with indoor lights which are your primary light source, place a large orange gel over the window. This filter is often called a CTO, short for color temperature orange. The CTO will change the color temperature of the light coming through the window from 5600K to 3200K, simulating lamp light.

For those situations when you have to combine indoor light with fluorescent, you have a couple of options. If your primary light source is incandescent, you can wrap the fluorescent tubes with a reddish brown gel, which removes the excess green from the light. This changes the color temperature from around 4300K to 3200K. If the fluorescent lights are your primary light source, you might place a bluegreen filter in front of your tungsten lights to give them the same color temperature as the fluorescent lighting.

If working with daylight and fluorescent lights, a magenta gel converts fluorescent to daylight. Conversely, a light green gel matches daylight to fluorescent.

All of the gels mentioned above come in various shades. If, for instance, you wish to give a shot a cooler feel, you can use a 1/2 CTB to only partially alter the color temperature of the outdoor light.

Sometime, you may find yourself in a situation where you have a large window with a beautiful view. You really want to use the window in your shot but the light coming from the outside is too bright. Don’t despair. Color correction gels can be combined with a gel called a neutral density gel or ND for short. This optically clear gel reduces the amount of light coming through the window without changing the color temperature. You can buy ND gels that reduce the amount of light by 1/2 (ND .15), 1 (ND.3), 2(ND.6) and 3(ND.9) complete stops.

You can also buy gels that combine color correction with neutral density properties. These combination gels are great to work with if you find yourself shooting interviews in offices with large windows. By taping sheets of the gel on the windows, you can not only change the color temperature of the light coming through, but also the intensity. Keep in mind, to your eye it may look very strange, but to the camera it will look great.


Soft and Color Corrected

In past columns we have talked about diffusing light so that it creates a soft look for lighting faces. What do you do if you have to correct the color temperature of the light and soften it, too? Reduce the amount of light shining on your subject by combining a diffusion gel with a color correction gel. Thankfully, there are diffusion gels with color correction added. There are also diffusion gels with ND filter properties so that you can turn your window light into a large soft light.


Final Thoughts

Anytime you have to mix indoor and outdoor light or incandescent with fluorescent, dig into your bag of tricks and pull out your color correction gels. Decide which light source is the easiest to control and gel that source.

A number of companies make fairly inexpensive gels that you can use to correct the color temperature of your light source. Check with your local video supply company.

Robert G. Nulph is an independent video/film producer/director and teaches video production courses at the college level.

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