EM Plane Wave: z Wave propagates along k, magnitude = 2p/l E and B constant on planar “phase front” k E and B are in phase E B x y

Energy density (J/m3) in an electrostatic field: Energy density (J/m3) in an magnetostatic field: Energy density in an electromagnetic wave is equally divided:

Rate of energy transport: Power (W) John Henry Poynting Rate of energy transport: Power (W) A cDt Power per unit area (W/m2): Pointing Vector Poynting

Poynting Vector oscillates very rapidly! Take the time average: “Irradiance” (W/m2)

EM radiation carries momentum: absorber Radiation pressure

Light is really made up of particles - photons absorber They carry energy: and momentum: “H-bar” is Planck’s constant:

Radiometry: the measurement of EM radiation Radiant Power Fe W Radiant Exitance Me W/m2 Irradiance Ee Radiant Intensity Ie W/sr Radiance (brightness) Le W/sr-m2 Le Me Fe Ee Ie W

Gamma ray X-ray UV Infrared radar radio l (meters) 10-15 10-12 10-9 10-6 10-3 1 103 Visible Light 400 nm 700 nm

Photometry: the measurement of EM radiation as perceived by the eye. equal radiance Luminous efficiency 1 (me) V(l) (you) 400 nm 700 nm (administrator)

Luminous Flux Fv lumen (lm) Luminous Exitance Mv lm/m2 Illuminance Ev lm/m2 or lux (lx) Luminous Intensity Iv lm/sr or candela (cd) Luminance (brightness) Lv cd/m2 or nit (Photometric value) = 685 x V(l) x (radiometric value)