Understanding the Principles of Light Behavior - Photographic Rendering with V-Ray for SketchUp - page 174

Using color temperature
In the nineteenth century, Glasgow born physicist Lord William Kelvin produced what
is now known as the Kelvin color temperature scale, which was based on his experi-
ments using a black body emitter (a block of carbon). On heating, the black body pro-
duced a range of colors that he noted followed a definite progression.
The Kelvin scale assigns a numeric value in degrees Kelvin to each step of that pro-
gression, from black through red, orange, white, and then beyond that into the blue
area of the color spectrum. Over the years, this scale has become so much a part
of the standards and terminology used in disciplines such as photography, stage and
film lighting, and now the creation of digital imagery, that anyone who wants to work
in these industries really needs to understand at least the basics of the Kelvin scale
and how it is used.
Often, you will hear a particular light type or maybe a lighting setup being referred to
as being warm or cool in nature. This temperature reference is taken from the Kelvin
scale itself. Of course, using the scale can on occasion become much more specific
and technical than simply using covering terms such as warm or cool. For instance,
light fixtures and bulb types will often have a Kelvin temperature or equivalent Cor-
related Color Temperature ( CCT ) associated with them, and as visualization artists,
our clients may at times request that the lighting we use on a particular project match
these exact specifications.
To help give you a quick idea of how the scale works, the overview table below lists a
number of Kelvin temperature ranges and matches a number of possible light sources
or types that would produce light at roughly those temperatures. This is by no means
an exhaustive list, but it will hopefully prove useful as a quick start reference guide. As
V-Ray lights don't currently make use of the Kelvin scale in order to set color values,
we have also included the closest equivalents in RGB color space.
The following table shows approximate light source colors using both degrees Kelvin
and RGB values: