3 TYPES OF SPECTRA (CONTINUOUS, EMISSION, ABSORPTION)
Prisms and diffraction gratings split light into the various wavelengths revealing a spectrum.
Light source
produces
various λs
Light beam of
those λs
Prism or
diffraction
grating
separates λs
Observer sees a
spectrum of
those λs
Eye sketch by
lilmizb3th.deviantart.com
Hand out diffraction gratings
1. Continuous spectrum
Ex: Spectrum of incandescent bulb
Pass around filament bulb
Describe: Rainbow like, All 
Source: Hot, dense object
Ex:
Filament, surface of sun (photosphere)
Light beam of all λs
Hot, dense
light source
produces all λs
Prism
separates
all λs
Observer sees a
spectrum of all λs,
namely a
continuous
spectrum
2. Emission spectrum
Ex: Spectrum of H gas tube
Note three lines (maybe four): red, turquoise, violet
Describe: Bright line
Source: Excited gas
Ex:
Gas discharge tube, gas clouds in outer space (Radio image of H in galaxy)
See http://www.jpl.nasa.gov/news/features.cfm?feature=573
Ex: Spectrum of He
Note: Must be a gas, Not H
Each element has a unique spectra. Different gases have different spectra
See http://blueox.uoregon.edu/~courses/BrauImages/Chap04/FG04_003.jpg
Hot gas
produces a
few λs
Light beam of
those few λs
Observer sees a
bright line
spectrum of those
few λs, namely an
emission spectrum
Prism
separates λs
3. Absorption spectrum
Ex: Use video camera to show spectrum of incandescent bulb through liquid
Describe: Missing colors or dark lines or bands, Continuous with certain  missing
Source: Hot dense object shining through a cooler gas cloud
Light beam
missing
those few λs
Hot, dense
light source
produces
all λs
Light beam
of all λs
A few λs are
absorbed in
gas cloud
Prism
separates
λs
Observer sees an
absorption spectrum,
most λs but missing
those few λs
absorbed by the gas
Summarizes all three
Uncertain source