The architecture of light: architectural lighting design concepts and techniques. A textbook of procedures and practices for the architect, interior designer and lighting designer pdfdrive com

2500 Kelvins: warm
3000 Kelvins: neutral
4100 Kelvins: cool
It is worth noting that with these engineered sources, the color temperature description has no relationship to the operating temperature
of the source itself. However, when we discuss incandescent or halogen incandescent sources, color temperature has more meaning. Because these light
sources are the product of heating a metal filament, the color temperature exhibited is related to the temperature of the filament. When we heat an incandescent filament to 2800 degrees Kelvin, we get light that we would describe as the “color” 2800 Kelvins (warm).
Where our engineered sources cause difficulty is when they are not labeled nor described by their Color Rendering Index, or numeric Color Temperature. Unfortunately, many consumer grade fluorescent light sources and LED’s are labeled with marketable names like “daylight white” or “designer white.” These names give no real hint as to the color temperature to expect and certainly tell nothing of the color rendering index. Thus, these products should be avoided when color rendering and source color are critical.
Knowing the Color Rendering Index and Color Temperature properties of
a light source is necessary for gaining a full understanding of a light source’s capability. It is reasonable to say Color Rendering Index is the more impacting of the two. If a source emits a complete spectrum of visible light and reveals every color accurately, it is really a matter of preference as to whether that source needs to appear warm or cool. This is just like daylight which changes color drastically from pale sunrise to deep sunset, but is always useful for revealing color. Conversely, if a light source reveals colors poorly, it is of little significance whether the source itself appears warm or cool to the eye. Many unsatisfactory lighting situations can be remedied by implementing light sources with a better color rendering index. Very few lighting problems can be solved just by addressing color temperature.
To make complete lighting decisions, it is necessary to understand and
specify both the Color Temperature and Color Rendering Index of a light source.