What is Incandescent sources? — Physics

Definition 11.12 High School Physics · Chapter 11 — Color and Light Sources

A source glowing because it is hot — flame, filament, star — shines by incandescence. Its spectrum is the continuous thermal spectrum of Chapter 2, and its peak obeys Wien’s law (Proposition 2.7),

\lambda_{\max} \times T = 2.90 \times 10^{-3}\,\mathrm{m}\,\mathrm{K},

our quantitative tool from now on: peak measured, temperature known.

Thermal spectra at 6000\, K and 3000\, K, peaks _ dashed at 483 and 967\, nm; the cooler curve, magnified twelve times, would otherwise hug the axis. — Thermal spectra at $6000\,\mathrm{K}$ and $3000\,\mathrm{K}$ , peaks $\lambda_{\max}$ dashed at $483$ and $967\,\mathrm{nm}$ ; the cooler curve, magnified twelve times, would otherwise hug the axis.

Examples

Example 11.13 (A very inefficient lamp)

A tungsten filament at $T = 2700\,\mathrm{K}$ peaks at $\lambda_{\max} = 2.90 \times 10^{-3}\,\mathrm{m}\,\mathrm{K}/2700\,\mathrm{K} = 1.07 \times 10^{-6}\,\mathrm{m} = 1070\,\mathrm{nm}$ , deep in the infrared: most of the electric power leaves as invisible radiation, only about $5\%$ as light — the incandescent bulb was mainly a heater.

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Examples

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