Color Temperatures The 2nd attribute of light
Approximate Color Consistency • Under normal conditions when we look at subject matter such as this, approximate color consistency comes into play and automatically makes a perceptual adjustment for these different sources of light. • For example, in the photo sources of light (sunlight on the right; a standard light bulb on the left) normally appear as white light to the eye. It's only when we see them together as we do here that the difference in color temperature becomes obvious
Approximate Color Consistency • Strangely, and maybe unfortunately, when we look at video or film, approximate color consistency doesn't work in the same way. Unless color corrections are made, we'll notice significant (and annoying) color shifts between scenes when they are cut together.
Basic Color Standards • Although light can be any color between infrared and ultraviolet, there are two basic color standards: • 3,200K (Kelvin) for incandescent lamps used in studios • 5,500K for average daylight
Sunlights’ Varying Color Temp. • The color of sunlight can vary greatly depending on the time of day, the amount of haze or smog in the air, and the geographic longitude and latitude of the area. • Because of its angle to the earth in the early morning and late afternoon, sunlight must travel through more of the earth's atmosphere.
Sunlights’ Varying Color Temp. • Note the different lengths of the red lines. The longer line in the drawing represents the sun's angle at sunrise or sunset. • During midday, the sun's rays have less distance to travel through the atmosphere and the temperature of direct sunlight at noon equals about 5,500K. (Depending on conditions, this number can be from 5,400 to 6,000K.)
Artificial Light Sources • 3,200K is the standard color temperature for TV lighting --considerably lower (redder) than average daylight. • This artificial type of lighting is commonly referred to as incandescent light, or tungsten light, after the coiled tungsten filament in these types of lamps. • Not all incandescent light is 3,200K. A common 100-watt light bulb, for example, is only about 2,850K. A candle flame (for those of you who have a need to shoot productions under candlelight!) is even redder-- about 1,900K.
Broken Spectrum Sources • CFL or Compact Fluorescent Lamps • Daylight Fluorescent Tubes • Color-Balanced Fluorescent Lamps(most common)
Broken Spectrum Sources • You may have noticed that sometimes videos and still photos shot under standard fluorescent lights often exhibit a greenish-blue cast. Fluorescent lamps belong to the group of lighting devices known collectively as discharge lamps -- glass tubes filled with metal vapor with electrodes at each end. • Unlike tungsten type lights, standard fluorescent lamps have a broken spectrum. Instead of a relatively smooth mix of colors from infrared to ultraviolet, standard fluorescent light has sharp bands or spikes of color -- primarily in the blue-green areas. Even though the eye will not notice these spikes, color shifts can result with video. • Although a blue-green cast used to be rather obvious in video shot under fluorescent lights, recent improvements in CCD/CMOS sensor color response have reduced the problem.
Compact Fluorescent Lamps • With energy saving compact fluorescent lamps (CFLs) seemingly destined to replace most tungsten lamps in the coming years, the color temperature characteristics of these lamps are now significant in videography. • The majority of CFLs on the market are between 2700K and 3000K, which is comparable to an incandescent bulb. However, "bright white," "natural" or "daylight" CFLs are also available in higher Kelvin color temperatures: 3500K, 4100K, 5000K, and 6500K. The latter enhance cooler colors -- blue, green, and violet, and dull down reds and yellows. • Because they are essentially fluorescent lamps, they have a broken spectrum that can result in unexpected color shifts with film and video. Before CFL lamps are used in critical color work the result should be checked on a good color monitor. If the color balance is not what you want, you should substitute lights of known color characteristics.
Daylight Fluorescent Tubes • Using a popular fluorescent tube, the daylight fluorescent, as an example, the average color temperature for this tube is 6,500K. Note that there are two "spikes" in the fluorescent spectrum (the green area in the illustration). • These spikes of high energy color cause the blue-green cast that we often see when we shoot under standard fluorescent illumination.
Color Balanced Fluorescent Lamps • Banks of color-balanced fluorescent lights produce a soft, virtually shadowless light over a wide area. • This type of light has been gaining popularity in many studio applications. Compared to traditional incandescent studio lighting, it generates much less heat and consumes much less energy. • However, since these fluorescent banks can't project light any great distance, their use is limited to subject matter that's relatively close to the lights. Often, color-balanced fluorescent banks are used to provide an over-all, even lighting, and more directional lighting instruments are then added as accent (key) lights
Color Temperature • Thanks to the human attribute of approximate color consistency, many of the color temperature problems we've discussed may not be obvious to the eye. But they can present major problems for video and film when you attempt to match successive scenes during editing. This represents just one type of technical continuity problem (scene-to-scene technical inconsistency) that you can encounter in video production.