Spark image
Infra red and energy distribution

These curves show that:
(a) the area between a energy-wavelength curve and the wavelength axis gives the total energy emitted by the body per unit area at that temperature
(b) the maxima of the curves is at shorter wavelengths at higher temperatures
(c) the curve for a lower temperatures lie inside those of a higher temperature

Wien's laws
(a) lmT = constant    lm is the wavelength at which most energy is emitted, the maxima of the curves, and the constant has a value of 2.898x10-3m K.
(b) the energy emitted at this wavelength (lm) is proportional to T5.

If lm for a black body lies in the red region of the spectrum the body will appear red hot, and as it gets hotter this peak will move towards the violet end of the spectrum. However this does not mean that the body will look “violet hot”. At the higher temperature all visible wavelengths will be present and so the body will appear “white hot”.

© Keith Gibbs 2011