“Heat creates light. It is the heat of a glowing ember or a burning candle that is responsible for the light.”
A brief History of Color Temperature
In the beginning there was fire.
Harnessed for light it became a campfire, a torch, a candle, an oil, a gas lamp.
Light from fire comes from the heat of the flame. The actual burning, or what is being burned, is of minor importance. Light from heat is called incandescent light.
The appearance of an incandescent light – its “color” – depends only on its temperature. Temperature can be measured in degrees Fahrenheit, or Celsius, or Kelvin. The choice of scale doesn’t matter: it just happens that for the purpose of lighting, engineers and scientists use the Kelvin (or K) scale.
Heat is not the only way to make light. Our current street lighting – “high pressure sodium” (HPS) – is the glow of a gas in a sealed tube caused by passing an electric current through the gas.
It is convenient to compare the “color” of the light from different sources to the “color” of the light from an incandescent source. The “temperature” of an HPS light, or a LED light, is the temperature of the incandescent light “closest” in apparent color.
But, “closest” doesn’t necessarily mean close. The strong, distinctive yellow glow a 2000 K HPS lamp doesn’t feel anything like the golden-amber of a 2000 K candle. To distinguish the “quality” of different lights of the same color temperature we need to dig a bit deeper. Read more at our discussion of Light Spectra…