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Color Temperature

written by: •edited by: Rhonda Callow•updated: 9/24/2009

What is color temperature? White light produces a spectrum of colors that can be measured with K (kelvin), a method used to measure different amounts of red and blue coming from a light source. Color temperature is important to consider, whether you’re working with film or video.

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    Color Temperature

    Color Temperature

    A British inventor, physicist, engineer, and mathematician by the name of Lord Kelvin (William Thomson) devised a method to measure color temperature by comparing the chromaticity of a light source with a black body radiator. When heated to match the same color of the light source, the black body produced different shades. Those black bodies below 4000 K produced reddish tones, and the black bodies 7500 K and above, looked bluish.

    Have you ever noticed how daylight on a cloudless day differs in color balance from a 75-watt household bulb? Daylight appears blueish, whereas indoor lighting has a orange-ish hue. This is because they have different color temperatures. It’s important to consider the various color temperatures a light source emits, whether you’re working with film or even with video. When working with film, you need to match a light source’s color temperature with the film stock’s color balance used (daylight or tungsten). Likewise, for video, it’s very important to do a proper white balance with a white card so that your footage won’t look unnatural. Please do not limit a color temperature to just ‘indoor’ or ‘outdoor’ lighting. There are various color temperatures in different light sources. For instance, have you noticed how fluorescent lights give off a greenish hue? Take a look at the following Kelvin scale of color temperatures.

    Kelvin Scale of color temperatures:

    0 K - midnight

    1800 K - candle flame

    2800 K - 75 watt bulb

    3000 K - sunrise/ sunset

    3200 K - tungsten-haologen lamp

    3500 K - home-type photo floodlight

    4000 K - warm fluorescent

    4800 K - fluorescent lamp

    5600 K - direct sunlight (noon)

    6500 K - overcasted sky

    7500 K - shade in daylight

    8000 K - blue sky

    12,000 K - twilight

    Working with color balancing is different between video and film. Even though doing this is much less cumbersome with video, if you want to mix different color temperatures in the same shot you will still need to plan accordingly. Let’s say you’re shooting a scene that has daylight entering through a large window with tungsten light sources inside. You’ll need to experiment different ways to achieve a nice look so that the daylight outside won’t look washed out or too white. Getting the desired look can become time consuming when balancing different color temperatures in the same shot, but, yes, there are ways to achieve the look you’re wanting.

    If the final look you’re wanting in this shot is a rich amber glow (tungsten), there are different ways to achieve this. First, in this particular example, consider matching all the light sources to one specific color temperature (either tungsten or daylight). What would be the most cost-effective approach? Using red gels over the window to turn daylight into tungsten may seem like a logical approach; however, it’s not just time consuming but also highly expensive and will require a well experienced crew. So, given you’re trying to first match all the light sources to one color temperature, another way to correct this is to place full blue gels over the light sources inside (keep in mind this will cut down the light sources by one f-stop), matching to the daylight outside. Next, to add a warmer tone in your image, you may choose to do either the following: have a video colorist fix this in post (this is quite expensive and time consuming.); a red 85 lens on the camera (since all the light sources now match daylight); or white balance to a light blue card (trick the camera into thinking the light blue is white). There is a professional brand known as WarmCards that do make light blue tinted cards to make warmer tones. All these techniques will produce warmer tones in your overall image. Above all else, don’t be afraid to experiment with the color temperatures you’re working with! After all, there are a number of ways to get the look you’re wanting.