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Controlling the Color of Light

Controlling the Color of Light

From yellow to blue, soft to harsh, indoor or out, the "color" of the scene changes with your light setup, and can influence the mood of your video.

From yellow to blue, soft to harsh, indoor or out, the "color" of the scene changes with your light setup, and can influence the mood of your video.

This is the time for walking down store aisles looking at colorful school supplies, buying new clothes for the kids, or dodging bright yellow busses full of eager students heading off to a new school year. It is a time of renewed energy and enjoying new experiences. That is until you look at the footage that you shot of your child's first day and the parade of busses and see that the busses are not yellow but a somewhat nasty shade of tan, the kids faces are bluish and you feel like you may have just produced the first reel of an alien invasion movie! The culprit? The camera was set for indoor lighting and you were shooting outdoors. In this column, we will look at color temperature and white balance. We will explain how you control the color temperatures of your light sources so that your subject's faces and the world around them actually look like they belong on this earth.

Color Temperature


All light sources have a distinct color that is rated using the Kelvin temperature scale. When we talk about color temperature, we are not talking about heat, but the color of the light that we see. Simply stated, indoor light is around 3200K, outdoor light is 5600K and fluorescents around 4200K. We use these numbers as starting points because in reality the color temperatures can vary quite a bit depending on the light source. For instance, outdoor color temperatures can range from 5000K to 12000K depending on cloud cover and time of day.

The human eye is capable of seeing many color temperatures of light at one time and interpreting the colors correctly so that when you are indoors, looking out a window, you see the grass as green and the sky as blue. You will also see white and colors correctly under the indoor light. Cameras however can only see one color temperature at a time. If your camera is set for daylight, it will see indoor lighting as very orange. This is why the photos you take in your living room without flash with daylight film look orange (or set to indoor on your digital camera). If your camera is set for indoors, the scene out your window will look very blue. When you white balance your camera, you are setting your camera to see white as white under the light in which you are shooting. The real trouble comes when you have multiple sources of light, each with a different color temperature.

Turning Indoor into Outdoor


If the interior location you are shooting in has a lot of windows and bright sunlight streaming in, don't close the curtains, use it. The light coming through the windows will make a great back light or fill light for your scene. However, what do you do about the video light you are going to use as your key light? It is rated at 3200K -- the indoor light setting. Simply attach a Color Temperature Blue (CTB) gel to the front of the light and it converts the light to 5600K and becomes an outdoor light! White balance your camera using the outdoor setting and you will have a beautifully lit scene.

Turning Outdoor Light into Indoor Light


If your interior setting has a few windows and you want to use the light as a fill light but your main light source will be video lights, you can also change outdoor light into indoor light. Get a sheet of Color Temperature Orange (CTO) gel and place it over the window. While to your eye it will look a little strange, to the camera, it will look as if it is seeing through a clear window and the sky will be blue, the leaves green and the school busses bright yellow.

Fluorescents


If you shoot video in offices, fluorescent light fixtures can cause a myriad of problems. When you white balance your camera to match the video lights you set up for your shoot, the fluorescent lights in the office will give surfaces a nasty green tint. You could turn out the office lights and just use your video lights, but that creates other problems such as a need for more fill light. Having enough fill makes the scene look more natural. What you can do is counter balance: either place an aqua colored filter in front of your video lights to convert them to the same color temperature of the fluorescents, or place reddish orange sleeves over the fluorescent tubes to convert them to the same color temperature as your video light kit.

Too Bright? Try an ND Filter


Sometimes, you may want to actually see the beautiful scene through a window as a backdrop. However, outdoor light is so much brighter than indoor light you would have to fry your talent to match the intensity. The answer? Neutral Density gels or ND gels for short. ND gels reduce the intensity of the light coming through the window while not changing the color temperature. They come in a variety of shades that are measured in the number of stops you want the light to be reduced. For example, an ND 3 filter reduces the light coming through the window by 1 stop. An ND 6 filter -- 2 stops. An ND 9 filter -- 3 stops.

If you want to combine a neutral density gel with CTO to convert the outdoor light to less intense indoor light, you can use a combination filter. While (to your eyes, anyway) it might appear that you have just placed a particularly nasty-looking brownish-orange film on your windows, your camera's image sensor will love it and will be dutifully capturing images of crystal-clear blue skies and lush, moist green grass.

The next time you go to a movie and see an office scene with the city shining outside the window, you can be assured that they have used color correcting gels.

Final Correction


While correcting the light from your lighting instruments or the windows is important, your hard work will only pay dividends if you remember to white balance every time you change positions. Even when shooting outdoors you can have a variety of color temperatures.

Take the time to white balance every time you change camera positions or directions. Remember, when your camera sees white as white, more than likely, the other colors in your scene will be right.

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

[Sidebar: Are you Gellin'?]


Gels used for color correction for video and film production can be found at any theatre and video production supply store or on the Web. Do a search for "video color gels." The three major suppliers of gel are Rosco, Lee and Gamcolor. The filters come in 20X24 sheets, 20-inch by 24-foot rolls, 48-inch by 25-foot rolls, extra wide 58-inch wide by 24-foot rolls for covering windows (CTO and ND filters) and sleeves for placing over fluorescent tubes. These gels are optically clear. If you are very careful to avoid air pockets and creases when placing the CTO and ND gels over windows, you should not be able to see them in the camera.

Tags:  September 2006
Dr. Robert G.
Nulph
Fri, 09/01/2006 - 12:00am