Glow (light emission)
| temperature | colour |
|---|---|
| 550 ° C | Dark brown |
| 630 ° C | Brownish red |
| 680 ° C | Dark red |
| 740 ° C | Dark cherry red |
| 780 ° C | Cherry red |
| 810 ° C | Light cherry red |
| 850 ° C | Bright red |
| 900 ° C | Good bright red |
| 950 ° C | Yellow Red |
| 1000 ° C | Light yellow bread |
| 1100 ° C | yellow |
| 1200 ° C | Light yellow |
| > 1300 ° C | Yellow white |
As Glut or annealing is defined as the visible radiation , emit the heated body. The state of such bodies is called incandescence . (In English the incandescent lamp is correctly called Incandescent light bulb .) As the temperature rises, the spectrum of the emitted light shifts to shorter wavelengths , the light becomes "bluer" (see also Wien's law of displacement ).
The radiation behavior of hot metals roughly corresponds to that of a black body . The temperature can be deduced from the color of the radiation (principle of a pyrometer ). The following classification of glow colors is common in iron smelting :
- Below 400 ° C: invisible infrared radiation
- 400 ° C: colorless gray glow when looking at night , only perceptible in the dark
- 525 ° C: Beginning red heat
- 700 ° C: dark red heat ( luminance approx. 1.5 cd / m²)
- 800 ° C: bright red heat (approx. 14 cd / m²)
- 1100 ° C: yellow glow (approx. 1,700 cd / m²)
- 1300 ° C: incipient white heat (approx. 16 thousand cd / m²)
- 1500 ° C: full, blinding white heat (almost 100 thousand cd / m²)
- 2000 ° C: (approx. 2 million cd / m²)
- 3000 ° C: (approx. 60 million cd / m²)
- 4000 ° C: (approx. 375 million cd / m²)
- 5000 ° C: (approx. 1.2 billion cd / m²)
- 5400 ° C: neutral white (approx. 1.7 billion cd / m²)
- 6000 ° C: (approx. 2.6 billion cd / m²)
- 8000 ° C: (approx. 7.3 billion cd / m²)
The names of the glowing colors are not to be taken too literally. In fact, even at a blackbody temperature of 1500 ° C, light is not a uniform mixture of visible light of all wavelengths. However, the color perception of the human eye is deceived by the dazzling brightness , since the high light intensity stimulates all irradiated color receptors in the retina and thus creates a white light impression. The reflection on a white surface appears reddish.
Actual incandescence, i.e. roughly equal proportions in the red and blue visible areas, is only reached above about 7000 ° C. The light of the sun with 5500 ° C (5778 K), for example, is almost white with a slightly smaller blue component and thus a yellowish impression if you reduce its brightness significantly.
Trivia
- Although, according to the radiation law, the total emitted energy increases with the fourth power of the temperature, the visual brightness of extremely hot radiators (several tens of thousands of Kelvin) only increases linearly with the temperature, since a large part of the radiation is emitted as invisible UV and X-rays.
- This light then also has a bluish color that is independent of the temperature.
example
The glass bulb of a halogen lamp reaches temperatures of more than 500 ° C, but it does not radiate in the visible range. (see black body ).
Web links
Individual evidence
- ^ Ulrich Fischer: Metal table book . 41st edition. Verlag Europa-Lehrmittel Nourney, Vollmer, 2001, ISBN 3-8085-1721-2 , p. 128B.
- ^ Lueger, Otto: Lexicon of the entire technology and its auxiliary sciences. Vol. 5, pp. 196-197, entry on incandescence