Color temperature

A method of indicating the temperature of a light-emitting object by corresponding it to the color of blackbody radiation, and the numerical value. When an electric heater is switched on in a pitch-black room, the color of the nichrome wire changes as the temperature rises. In this way, an object emits radiation (thermal radiation) according to its temperature, but the amount of radiation of each wavelength varies depending on the temperature, and the difference in the visible light portion is perceived as a difference in color. Since radiation methods differ depending on the surface properties even at the same temperature, a blackbody is considered as a standard object, and when the color of light emitted by a general object (excluding reflected light) appears to be the same as the color of blackbody radiation at temperature T , the color temperature of the object is said to be T. Color temperature and the true temperature of an object are not necessarily the same. Also, there are colors such as pink that cannot be expressed by color temperature, so its use is limited to light sources. When you buy a fluorescent lamp, the color temperature is often written on the box. Note that color temperature has nothing to do with the commonly known warm colors (red, yellow, orange) and cool colors (purple, blue).

[Koide Shoichiro]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

黒体放射の色と対応させて、発光物体の温度を表示する方法、またその数値。真っ暗な室内で電熱器のスイッチを入れると、温度があがるにつれてニクロム線の色が変わっていく。このように物体はその温度に応じた放射（熱放射）を出すが、どの波長の放射をどれだけ出すかは温度で違い、可視光部分のその差が色の違いとして感じられる。同じ温度でも表面の性質で放射の仕方は異なるので、標準物体として黒体を考え、一般の物体が出す光（反射光を除く）の色が温度Tの黒体放射の色と同じに見えるとき、物体の色温度はTであるという。色温度と物体の本当の温度とはかならずしも等しくはない。またピンクなど、色温度によっては表せない色もあるので、利用は光源などに限られる。蛍光灯を買うと、箱に色温度について書いてあることが多い。なお、色温度は俗にいう暖かい色（赤、黄、橙(だいだい)）、冷たい色（紫、青）とは関係がない。

［小出昭一郎］

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例