1. What is a Spectrum? How much of observed light is high energy radiation and how much is low energy radiation.

2. 2 Nature of Light Properties Short wavelength, λHigh Frequency, νHigh Photon EnergyBlue Long wavelength, λ Low Frequency, νLow Photon EnergyRed Small Amplitude - FaintLow Photon Flux Faint Large Amplitude - BrightHigh Photon Flux Bright

3. 3 What is a Spectrum Brightness or Intensity as a function of Energy – Flux as function of Energy – How many photons have what energy? – How many waves of a certain wavelength or frequency have what amplitude?

4. How many photons (brightness or flux) have what energy (wavelength, frequency)? High energy Low energy High energy Low energy In the wavelength range 450nm to 750nm, the Sun emits… …more high energy (blue) photons. …fewer low energy (red) photons. Particle (photon) view of light

5. What is the amplitude (brightness or flux) of light waves of different energy (wavelength, frequency)? High energy Low energy High energy Low energy In the wavelength range 450nm to 750nm, the Sun emits… …short-wave (blue) light with large amplitude. …long-wave (red) light with small (or low) amplitude. Wave view of light

6. 6 What is a Spectrum Brightness or Intensity as a function of Energy May equivalently shown be shown as a function of wavelength or frequency Describes the energy distribution of the observed light, or Describes how much of the observed light has what energy value