What is Correlated Color temperature (CCT)?
Based on human visual sense, Correlated Color Temperature (CCT) is the extent of how “Orange’ish” (Warm) or “Blue’ish” (Cold) that a light emitted from a light source appears. In daily life, we measured the color temperature in Kelvin and we commonly found that the color temperature is about 2700 Kelvin to 6500 Kelvin in film and video lighting.
The higher this number is, the cooler the light source is. And vice versa. For example, warm lights have a low CCT, such as incandescent bulbs. And cold lights have a high color temperature, such as fluorescent lamps.
If filmmakers or gaffers are not familiar with the parameter of CCT, what can they do? Not all filmmakers or gaffers are familiar with the usage of color temperature. Instead, they prefer to use some typical name in the production industry for a better understanding of lighting conditions. The chart below listed some typical light sources and their corresponding color temperatures as reference.
|Color Temperature||Light Source|
|2500-3500 K||Tungsten Bulb (household variety)|
|3000-4000 K||Sunrise/Sunset (clear sky)|
|4000-5000 K||Fluorescent Lamps|
|5000-5500 K||Electronic Flash|
|5000-6500 K||Daylight with Clear Sky (sun overhead)|
|6500-8000 K||Moderately Overcast Sky|
|9000-10000 K||Shade or Heavily Overcast Sky|
Color consistency (SDCM) and color temperature.
Color consistency is one expression to describe how consistent the color temperature of lamps is. And how to judge if the color temperature of a lamp is consistent or not, we need to know two
SDCM is the short name of Standard Deviation of Color Matching, which is also the same as “MacAdam Ellipse”.
MacAdam Ellipse is the system for measuring how much color deviation is. A series of ellipses ranking from 1 to 7 steps describe the color consistency of lights. The ellipses can be located around any target color temperature. The lower number of ellipses is, the less color deviation is.
If the number is higher than 3-step SDCM, the difference of light would be noticeable by human eyes, which means the color consistency is poor. For professional lighting, the color consistency with MacAdam Ellipse below 3 steps SDCM is necessary.
2. Color temperature tolerance
Due to the LED manufacture technology, all LED lights are not able to be exactly the same in color temperature. Therefore, there will be a range of tolerance towards target color temperature. And to understand if the color temperature tolerance is well or not for film and video production light, SDCM is involved in the judgment as well. The chart below is an evaluated relationship between color temperature tolerance and MacAdam Ellipse steps (SDCM).
Why color temperature or color consistency is important for film and video lighting.
When starting a film production, as a camera man, in addition to the art-work of light and shadows, what needs to be considered the most should be white balance. And CCT is one of the key facts related to white balance. If the color temperature is inconsistent, it would increase the difficulty in white balance adjustment and eventually impact the project efficiency and the final footage result. And for sure, it will also cause more extra work for post-production and consequently increase the cost in money and time.
For example, if we choose daylight (5600K) cheap light with bad color temperature consistency, and if the color temperature tolerance of it is ±500K, as a result, the true color temperature in practice could probably be about 5100K or 6100K instead of 5600K true daylight color temperature. If we set and adjust the white balance of the camera with 5600K daylight, the footage would be yellow’ish or blue’ish.