How do element "lamps" allow us to observe multiple electron transitions?

Question

The way that chemistry students are usually introduced to the concept of atomic spectra is through a discussion of element "lamps" - like the helium lamp or the hydrogen lamp. (Consider, for example, the images at http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/atspect.html.) I do not understand why splitting the light emitted from these lamps (by using, say, a prism) allows us to see a myriad of colors as opposed to just one color. How do these element lamps energize the electrons in such a way that we see wavelengths of light corresponding to multiple electron transitions instead of just one? (When one conducts a flame test for metallic ions, for example, one sees only a single color, not multiple ones...unless I've got it all wrong.)

Answer 1

The difference is in the mechanism of light production. With ionized gases, the light comes from the discrete units of energy released as electrons drop to lower energy states. If you look at a light source that emits light due to heat, then it follows the blackbody radiation law, and emits a continuum of frequencies. Even the flame test viewed through a prism is going to have a spectrum in addition to the color perceived when viewing it directly--just as the light from the yellow sun is comprised of the colors of the rainbow.