Kirchoff's Law I: Continuum Spectrum.
In such a spectrum, intensity (brightness) changes smoothly with wavelength and all colors are present. There is no black in this spectrum. This is what the spectrum of a Black Body (such as the very hot element at the center of a light bulb) looks like:
Kirchoff's Law II: Emission-Line Spectrum.
The light is emitted only at a few particular wavelengths, while most of the spectrum is BLACK. The pattern of lines shown could be used to tell us what the hot gas is made up of! This is typical of hot, tenuous gas (such as in a neon-tube):
Kirchoff's Law III: Absorption-Line Spectrum.
Here, we see a continuum spectrum, but it is missing discrete wavelengths, making specific points in the spectrum appear BLACK. This is what occurs when a cool, tenuous gas resides in front of a bright continuum source, it absorbs out (removing) light at specific wavelengths.
