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What is luminous temperature?

In applied lighting engineering it is appropriate to associate the luminous temperature of different types of candlelight sources with natural sources of light.

To provide comprehensible classification of white lamps chrominance it is customary to divide all the sources into three groups: warm white, neutral white and cold white, or daylight.

Luminous temperature scale can be divided into three bands:

Warm white

1850-2000K

Among the sources of artificial light, reproducing this temperature one should name the flame of the stearin candle. The natural source of light is morning or evening twilight sky (2000K).

In practice:

The warm light sources, as incandescent lamps or low-voltage halogen lamps, have almost the same luminous temperature as the real temperature of the glower.

2000-2700K

Sources of artificial light, reproducing such luminous temperature are incandescent lamps and sodium high-pressure lamps. The natural source of light is sky at sunrise- or sunset time (2300-2500 K)

Practice:

While the current , passing through the glower, is being decreased, it is not only the light flux that is being changed, but also the chrominance of radiation, that is getting warmer (redder). In such a way while dimming the incandescent lamp of greater capacity one can lower luminous temperature, keeping at the same time the necessary level of illumination. Halogen lamps have greater temperature of the glower, that is why their color is accepted as a colder one.

2700 – 2800 К

Candlelight sources, reproducing this illuminating temperature are incandescent lamps, line voltage halogen lamps, luminescent lamps, compact luminescent lamps, light diodes (LED).

Practice:

Luminescent lamps, gas-discharge lamps of high pressure and light diodes reproduce different illuminating temperatures. That is why it is necessary to point out the exact illuminating temperature of the applied source.

2800 – 3500 К

Candlelight sources, reproducing this illuminating temperature are incandescent lamps, line voltage halogen lamps, low-voltage halogen lamps, luminescent lamps, compact luminescent lamps, LED.

Practice:

Sensitivity of human eye to the illuminative temperature has nonlinear dependence. Difference of 500K in a warm part of diapason is more noticable, than the same difference in a cold part of it. That is why light sources producers offer greater range of chromaticity in a warm diapason. 

            3500 К

Candlelight sources, reproducing this illuminating temperature are line voltage halogen lamps, low-voltage halogen lamps, luminescent lamps, compact luminescent lamps, metal-halide lamps, LED. Natural source of light is the Sun an hour after the rise of before the dawn.

Practice:

Neutral white

            4000 К

Candlelight sources, reproducing this illuminating temperature are luminescent lamps, compact luminescent lamps, metal-halide lamps, LED. Natural source of light is the Moon (4125 K).

Practice:

Dimming the luminous flux of gas-discharge luminiscent and compact luminiscent lamps, one won’t change chromaticity of their illumination.  

Cold white

            5000 К

Candlelight sources, reproducing this illuminating temperature are luminescent lamps, compact luminescent lamps, metal-halide lamps, LED. Natural source of light is morning or evening Sun in the clear sky at an angle of 15 degrees over the skyline.(3600 – 5000 К).

            5500 К

Candlelight sources, reproducing this illuminating temperature are luminescent lamps, compact luminescent lamps, metal-halide lamps, LED. Natural source of light is the midday Sun by the light cloudiness (5100 -5600 К).

            6500 К

Candlelight sources, reproducing this illuminating temperature are luminescent lamps, compact luminescent lamps, metal-halide lamps, LED. Natural source of light is the summer Sun at the peak in the clear blue sky. (6000 – 6500 К).

            7000 К

Candlelight sources, reproducing this illuminating temperature are metal-halide lamps and LED. The natural source of light is the sky daylight by high, light clouds. (6700 -7000 К).

            12000 К

The natural source of light is the sky daylight by light cloudiness (12 000 – 14 000 К). The illuminating temperature of the clear blue sky reaches 15 000 – 27 000 К.

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