Color Temperature

The concept of color temperature is fundamentally derived from black-body radiation, a phenomenon described by Max Planck in 1900. A black body is a theoretical object that absorbs all incident electromagnetic radiation and, when heated, emits radiation with a spectral distribution dependent only on its temperature. As the temperature of this black body increases, the light it emits shifts from red, to orange, to yellow, to white, and finally to a bluish-white. This sequence of colors provides a one-dimensional scale to characterize light sources.

For example, a traditional incandescent bulb, which works by heating a filament until it glows, is a close approximation of a black-body radiator. Its warm, yellowish light has a color temperature of around 2700 K. In contrast, the midday sun, which appears as a neutral white, has a much higher color temperature of about 5500-6500 K. This scale is counter-intuitive to cultural associations of color, where red is ‘hot’ and blue is ‘cool’. In physics, a higher color temperature corresponds to a ‘cooler’, more bluish light. This metric is only truly applicable to light sources that have a spectrum similar to a black-body radiator.