Light Visible electromagnetic radiation Power spectrum Polarization Photon
Light Visible electromagnetic radiation Power spectrum Polarization Photon (quantum effects) From London and Upton Wave (interference, diffraction) CS 348 B Lecture 4 Pat Hanrahan, 2005
Topics Light sources and illumination Radiometry and photometry Quantify spatial energy distribution n Radiant intensity n Irradiance n Inverse square law and cosine law n Radiance n Radiant exitance (radiosity) Illumination calculations n Irradiance from environment CS 348 B Lecture 4 Pat Hanrahan, 2005
Radiometry and Photometry
Radiant Energy and Power: Watts vs. Lumens n Energy efficiency n Spectral efficacy Energy: Joules vs. Talbot n Exposure n Film response n Skin - sunburn CS 348 B Lecture 4 Luminance Pat Hanrahan, 2005
Radiometry vs. Photometry Radiometry [Units = Watts] n Physical measurement of electromagnetic energy Photometry and Colorimetry [Lumen] n Sensation as a function of wavelength n Relative perceptual measurement Brightness [Brils] n Sensation at different brightness levels n Absolute perceptual measurement n Obeys Steven’s Power Law CS 348 B Lecture 4 Pat Hanrahan, 2005
Blackbody Radiation CS 348 B Lecture 4 Pat Hanrahan, 2005
Tungsten Lamp CS 348 B Lecture 4 Pat Hanrahan, 2005
Fluorescent Bulb CS 348 B Lecture 4 Pat Hanrahan, 2005
Sunlight CS 348 B Lecture 4 Pat Hanrahan, 2005
Radiant Intensity
Radiant Intensity Definition: The radiant (luminous) intensity is the power per unit solid angle emanating from a point source. CS 348 B Lecture 4 Pat Hanrahan, 2005
Angles and Solid Angles n Angle circle has 2 p radians n Solid angle sphere has 4 p steradians CS 348 B Lecture 4 Pat Hanrahan, 2005
Differential Solid Angles CS 348 B Lecture 4 Pat Hanrahan, 2005
Differential Solid Angles CS 348 B Lecture 4 Pat Hanrahan, 2005
Isotropic Point Source CS 348 B Lecture 4 Pat Hanrahan, 2005
Warn’s Spotlight CS 348 B Lecture 4 Pat Hanrahan, 2005
Warn’s Spotlight CS 348 B Lecture 4 Pat Hanrahan, 2005
Light Source Goniometric Diagrams CS 348 B Lecture 4 Pat Hanrahan, 2005
PIXAR Light Source Shadows Shadow Matte Projected Slide Texture CS 348 B Lecture 4 Uber. Light( ) { Clip to near/far planes Clip to shape boundary foreach superelliptical blocker atten *= … foreach cookie texture atten *= … foreach slide texture color *= … foreach noise texture atten, color *= … foreach shadow map atten, color *= … Calculate intensity fall-off Calculate beam distribution } Pat Hanrahan, 2005
Radiance
Radiance Definition: The surface radiance (luminance) is the intensity per unit area leaving a surface CS 348 B Lecture 4 Pat Hanrahan, 2005
Typical Values of Luminance [cd/m 2] Surface of the sun 2, 000, 000 nit Sunlight clouds Clear day Overcast day Moon CS 348 B Lecture 4 30, 000 300 0. 03 Pat Hanrahan, 2005
Irradiance
The Invention of Photometry Bouguer’s classic experiment n Compare a light source and a candle n Intensity is proportional to ratio of distances squared Definition of a candela n Originally a “standard” candle n Currently 550 nm laser w/ 1/683 W/sr n 1 of 6 fundamental SI units CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance Definition: The irradiance (illuminance) is the power per unit area incident on a surface. Sometimes referred to as the radiant (luminous) incidence. CS 348 B Lecture 4 Pat Hanrahan, 2005
Lambert’s Cosine Law A CS 348 B Lecture 4 Pat Hanrahan, 2005
Lambert’s Cosine Law A CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance: Isotropic Point Source CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance: Isotropic Point Source CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance: Isotropic Point Source CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance: Isotropic Point Source CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance: Isotropic Point Source CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance: Isotropic Point Source CS 348 B Lecture 4 Pat Hanrahan, 2005
Directional Power Arriving at a Surface CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance from the Environment Light meter CS 348 B Lecture 4 Pat Hanrahan, 2005
Typical Values of Illuminance [lm/m 2] Sunlight plus skylight (overcast) Interior near window (daylight) Artificial light (minimum) 100, 000 lux 10, 000 100 Moonlight (full) 0. 02 Starlight 0. 0003 CS 348 B Lecture 4 Pat Hanrahan, 2005
The Sky Radiance Distribution From Greenler, Rainbows, halos and glories CS 348 B Lecture 4 Pat Hanrahan, 2005
Gazing Ball Environment Maps Miller and Hoffman, 1984 Photograph of mirror ball n Maps all spherical directions to a to circle n Reflection direction indexed by normal n Resolution function of orientation n CS 348 B Lecture 4 Pat Hanrahan, 2005
Environment Maps Interface, Chou and Williams (ca. 1985) CS 348 B Lecture 4 Pat Hanrahan, 2005
Irradiance Environment Maps R Radiance Environment Map CS 348 B Lecture 4 N Irradiance Environment Map Pat Hanrahan, 2005
Irradiance Map or Light Map Isolux contours CS 348 B Lecture 4 Pat Hanrahan, 2005
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) CS 348 B Lecture 4 Pat Hanrahan, 2005
Directional Power Leaving a Surface CS 348 B Lecture 4 Pat Hanrahan, 2005
Uniform Diffuse Emitter CS 348 B Lecture 4 Pat Hanrahan, 2005
Projected Solid Angle CS 348 B Lecture 4 Pat Hanrahan, 2005
Uniform Diffuse Emitter CS 348 B Lecture 4 Pat Hanrahan, 2005
Radiometry and Photometry Summary
Radiometric and Photometric Terms CS 348 B Lecture 4 Pat Hanrahan, 2005
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 CS 348 B Lecture 4 Pat Hanrahan, 2005
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