Planck's law describes the spectral radiance of electromagnetic radiation at all wavelengths from a black body at temperature T. As a function of frequency ?, Planck's law is written as
   $I(\nu,T) = \frac{2 h\nu^3 }{c^2} \frac{1}{e^{h\nu/kT}-1}$ or  [img]http://upload.wikimedia.org/math/9/7/4/974887ba0f7030f31b7b27b619afde87.png[/img]

It can be converted to an expression for I'(?,T) in wavelength units by substituting ? by c / ? and evaluating

  $ I'(\lambda,T) = I(\nu,T)\left|\frac{d\nu}{d\lambda}\right| $ or [img]http://upload.wikimedia.org/math/2/7/a/27aa3105194d765b91f845f50968e7cf.png[/img]

$\frac{2 h\nu^3 }{c^2}=\frac{2 h(c\lambda)^3 }{c^2}=\frac{2hc}{\lambda^3}$
and from $\nu= c\lambda$, we have
$d\nu=-\frac{c}{\lambda^2}d\lambda$
so
$I(\lambda,T)=\frac{2hc^2}{\lambda^5}\frac{1}{e^{hc/\lambda kT}-1}$ or [img]http://upload.wikimedia.org/math/1/0/c/10c96a8f2af7d9631a0f4dde5b817b62.png[/img]
The above equation is energy per unit wavelength per unit solid angle.

This applets will show six black cureves of blackbody radiation curve betwen Tmin and Tmax.
Another curve in red is also shown (it's temperature can be adjusted with left slider bar)
Maximum wavelength shown can be adjusted with right slider bar.
You can use it for study the intensity for blackbody radiation.
If you want to study different temperature range, You can change Tmin and Tmax, to change the temperature range,too.
The wavelength unit in the simulation is (angstrom).
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[img]http://upload.wikimedia.org/math/3/6/c/36c7c70624f4ed44af2f004c87bf22c4.png[/img] is the spectral energy density function with units of energy per unit wavelength per unit volume.