Light, according to Wikipedia, is an electromagnetic radiation of a wavelength visible to the human eye, but in general, Light can be an electromagnetic radiation of any wavelength, regardless if it is visible to the human eye or not. For this entry, the emittance spectra of different light sources will be observed.
Figure 1: Emittance Spectrum for a Blackbody radiator at different temperatures.
Notice that in figure 1, the temperature is directly proportional to the emittance of the blackbody radiator; as the temperature increases, so does the peak of the emittance. Also, as the temperature is increased, the peak seems to be shifted to the left. The emittance spectra of the blackbody radiator is given by
where h is the Planck's constant, lambda is the wavelength of radiation, c is the speed of light and T is the temperature in Kelvins. The range for the wavelength is from 350nm to 750nm, which is the range for visible light. For the case of temperatures about 6500 K and 5400 K, a color of bluish green can be observed.
Below are some of the emittance spectra of common light sources.
Figure 2: Emittance for a Light Emitting Diode.
Figure 3: Emittance Spectra for a lighter that uses butane.
Figure 4: Emittance Spectra for a Mercury Lamp.
These emittance spectra were experimentally gathered using a portable spectrometer. Note that the peaks indicate the wavelength (and hence the color) in which the human eye can see the radiation. For the LED, it is expected to see a bluish-green color, while for the lighter that uses butane, it is expected to observe a yellowish color and for the the mercury lamp, a combination of bluish green and light green is expected.
It is important to at least be familiar with these emission spectra because, depending on the application, certain emittance spectra are required for certain applications.
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