Bright-Line Spectra of Hydrogen and Helium

Wave model
Wavelengths of radiation vary
Radio waves measure up to several kilometers long
Gamma ray waves are less than a billionth of a centimeter long
White light consists of several wavelengths corresponding to the colors of the rainbow

Particle model
Particles called photons
Exert a pressure, called radiation pressure, on matter
Shorter wavelengths correspond to more energetic photons

Spectroscopy
The study of the properties of light that depend on wavelength
The light pattern produced by passing light through a prism, which spreads out the various wavelengths, is called a spectrum (plural: spectra)

Types of spectra
Continuous spectrum
Produced by an incandescent solid, liquid, or high pressure gas
Uninterrupted band of color
Dark-line (absorption) spectrum
Produced when white light is passed through a comparatively cool, low pressure gas
Appears as a continuous spectrum but with dark lines running through it

Bright-line (emission) spectrum
Produced by a hot (incandescent) gas under low pressure
Appears as a series of bright lines of particular wavelengths depending on the gas that produced them