[quote author=Fu-Kwun Hwang link=topic=427.msg1240#msg1240 date=1172389144]

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.
[img]http://upload.wikimedia.org/math/3/6/c/36c7c70624f4ed44af2f004c87bf22c4.png[/img] is spectral energy density function with units of energy per unit wavelength per unit volume.
[/quote]

Question1:
In school, i taught intensity = power / area.
so actually what the y-axis is displaying is intensity/ wavelength ?
[img]http://upload.wikimedia.org/math/3/6/c/36c7c70624f4ed44af2f004c87bf22c4.png[/img] is spectral energy density function with units of energy per unit wavelength per unit [color=blue][b]area[/b][/color] [s]volume.[/s]

Suggestion:
Should the applet called it energy density function with units of energy per unit wavelength per unit [color=blue][b]area[/b][/color]


Question2:
in your current XML
eightpihc2 = 8*pi*h*c*c*1.e40
but i don't understand why [img]http://upload.wikimedia.org/math/3/6/c/36c7c70624f4ed44af2f004c87bf22c4.png[/img] has only 1 c, if you code is 2 c's

Is the image wrong?


Question3:
what is the url of the wikimedia.org? for the picture http://upload.wikimedia.org/math/3/6/c/36c7c70624f4ed44af2f004c87bf22c4.png
maybe i can go read a bit to understand more

Where did you find this equation :)
i look through
http://en.wikipedia.org/wiki/Thermal_radiation
http://en.wikipedia.org/wiki/Black_body
but no [img]http://upload.wikimedia.org/math/3/6/c/36c7c70624f4ed44af2f004c87bf22c4.png[/img]