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White Balance

Physics Of Light (1 MB)

White light is a result of all parts of the visible color spectrum being emitted by the light source. When we talk of white-balancing a camera, we have generally assumed that the light source includes the full range of frequencies in the visible spectrum of light. The relative strength of these frequencies varies, usually skewing toward the red or blue end. The "color" of the light is an indication of which parts of the visible light spectrum are strongest in the light source. In general terms, this is often thought of as "daylight" vs. "indoor" or "artificial" light, daylight being bluish and indoor light being reddish. This quality of "color" of light is most often expressed in terms of Kelvin color temperature. The higher the Kelvin temperature, the bluer the light. In fact, the process is much more complicated than that.

For example, outdoor light is affected by the time of day and cloud conditions. Clouds or shade make light even bluer, while the setting sun's light is closer to the yellow-orange light associated with indoor light. This is because of atmospheric effects that reflect and/or absorb parts of the sun's rays. Indoor light on the other hand may be a mixture of normal household lamps, fluorescent lights and daylight coming in thru windows. Even more complicating are industrial light sources (such as sodium vapor, mercury vapor and other specialty lighting). Industrial lighting is chosen for intensity rather than color purity, frequently using interrupted spectrum sources that emit unusual spikes in the spectrum or that lack parts of the spectrum entirely, resulting in strong color casts (green under fluorescents) or an absence of certain colors entirely (low pressure sodium oxide street lights create an almost monochromatic look because they are exclusively in a yellow part of the spectrum so that color will be muted or fail to reproduce outside of yellows).

Daylight can be matched artificially indoors by using specialty lighting including HMI (Hydro Mercuric Iodide) lights and specially balanced fluorescent lighting (not available at the local hardware store and quite a bit more expensive, also available to match indoor lighting without the green spikes).

White balancing allows the camera to define what the color white is under any of these various lighting conditions. Bear in mind that white is a relative term and varies depending on pigments, dyes and even fabric "white enhancers". Ideally, white balancing should be done to a "gray" card or other specially calibrated source that is controlled to reflect light equally from across the spectrum. There are also "blue" cards, calibrated specifically to produce slightly "warmer" colors, usually to make skin tones more pleasing. White balancing will not correct for parts of the spectrum not present from the light source.

ALWAYS WHITE BALANCE BEFORE SHOOTING AND ANYTIME LIGHTING CONDITIONS CHANGE!!! Failure to white balance could result in an unsightly, unnatural color cast

Physics Of Light | Why White Balance | How To White Balance