Light Visible electromagnetic radiation Power spectrum From London

Light Visible electromagnetic radiation Power spectrum From London and Upton Polarization Photon (quantum effects) Wave (interference, diffraction)

Topics Light sources and illumination Radiometry and photometry Quantify spatial energy distribution n Radiant intensity n Irradiance n n n Inverse square law and cosine law Radiance Radiant exitance (radiosity) Illumination calculations n Irradiance from environment

Radiometry and Photometry

Radiant Energy and Power: Watts vs. Lumens Energy efficiency n Spectral efficacy n Energy: Joules vs. Talbot n Exposure n Film response n Skin - sunburn Luminance

Radiometry vs. Photometry Radiometry [Units = Watts] n Physical measurement of electromagnetic energy Photometry and Colorimetry [Lumen] n n Sensation as a function of wavelength Relative perceptual measurement Brightness [Brils] n n n Sensation at different brightness levels Absolute perceptual measurement Obeys Steven’s Power Law

Radiant Intensity

The Invention of Photometry Bouguer’s classic experiment • Compare a light source and a candle • Intensity is proportional to ratio of distances squared Definition of a candela • Originally a “standard” candle • Currently 550 nm laser w/ 1/683 W/sr • 1 of 6 fundamental SI units

Radiant Intensity Definition: The radiant (luminous) intensity is the power per unit solid angle emanating from a point source. 683 lumens/watt @ 555 nm

Angles and Solid Angles • Angle circle has 2 p radians • Solid angle sphere has 4 p steradians

Differential Solid Angles

Differential Solid Angles

Isotropic Point Source

Warn’s Spotlight

Warn’s Spotlight

Light Source Goniometric Diagrams

Radiance

Radiance Definition: The surface radiance (luminance) is the intensity per unit (projected) area leaving a surface

Typical Values of Luminance [cd/m 2] Surface of the sun 2, 000, 000 nit Sunlight clouds 30, 000 Clear day 3, 000 Overcast day 300 Moon 0. 03

The Sky Radiance Distribution From Greenler, Rainbows, halos and glories

Environment Maps Interface, Chou and Williams (ca. 1985)

Gazing Ball Environment Maps Photograph of mirror ball Miller and Hoffman, 1984 n Maps all spherical directions to a to circle n Reflection direction indexed by normal n Resolution function of orientation n

Irradiance

Irradiance Definition: The irradiance (illuminance) is the power per unit area incident on a surface. Sometimes referred to as the radiant (luminous) incidence.

Lambert’s Cosine Law A

Lambert’s Cosine Law A

Irradiance: Isotropic Point Source

Irradiance: Isotropic Point Source

Irradiance: Isotropic Point Source

Irradiance: Isotropic Point Source

Irradiance: Isotropic Point Source

Irradiance: Isotropic Point Source

Directional Power Arriving at a Surface

Irradiance from the Environment Light meter

Typical Values of Illuminance [lm/m 2] Sunlight plus skylight (overcast) Interior near window (daylight) Artificial light (minimum) Moonlight (full) Starlight 100, 000 lux 10, 000 100 0. 02 0. 0003

Blackbody Radiation

Tungsten Lamp

Fluorescent Bulb

Sunlight

Irradiance Environment Maps R Radiance Environment Map N Irradiance Environment Map

Irradiance Map or Light Map Isolux contours

Radiant Exitance (Radiosity)

Radiant Exitance Definition: The radiant (luminous) exitance is the energy per unit area leaving a surface. In computer graphics, this quantity is often referred to as the radiosity (B)

Directional Power Leaving a Surface

Uniform Diffuse Emitter

Projected Solid Angle

Uniform Diffuse Emitter

Radiometry and Photometry Summary

Radiometric and Photometric Terms

Photometric Units “Thus one nit is one lux per steradian is one candela per square meter is one lumen per square meter per steradian. Got it? ”, James Kajiya