The incandescence of objects at any temperature can be predicted using Planck's law, which assumes an object is a black body radiator. A black body radiator emits only its own light and does not reflect outside light. Planck’s law describes the energy intensity of all the different colors, or wavelengths of light, emitted. 

Planck's Law: 

gives the total energy radiated from the object ( ), in watts per square centimeter, as a function of wavelength (  ), in micrometers ( µm ) and the surface temperature ( T ), in Kelvin.

The color of the light emitted is related to the wavelength at which the light intensity is greatest, which is given by Wien’s law (obtained from Planck’s law by differentiation):

                   Wien’s Law: _max T  =  2898

where, _max is the emission wavelength with the greatest intensity and T is the surface temperature.

Together, these laws predict the light given off by a light bulb or any incandescent source. Use the interactive incandesent spectrometer below to explore the color/wavelength and intensity of light given off from any incandescent light source as a function of it's temperature.  The sliding bar controls the temperature.  The intensity of visible light is proportional to the area under the curve in the visible (colored) region of the spectrum.  The color of the light given off  results from the combined intensity of the various wavelengths of visible light emitted.  The light to the right of the visible region is in the infrared region of the spectrum.  The light to the left is in the ultraviolet region. 

Use the Interactive Incandescent Spectrometer to explore the relationship between light emission and temperature.

After you have explored the relationship between temperature and the wavelength, color and intensity of light, take the following quiz. You can always go back to the applet, to arrive at your answers.