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Draw a graph of the illuminance produced by a lamp. with a luminous flux of 2275 lm at distances from 0.50 m to 5.0 m. SOLUTION: SOLUTION: 3. A 64-cd point source of light is 3.0 m away from a painting. What is the illumination on the painting in.
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- Geometric Modeling
- Lighting & Materials
- Cameras & Imaging
- Today
- Radiometry
- Assumption: geometric optics model of light
- Example Light Measurements of Interest
- Radiant Intensity
- as a direction vector
- Polar AKA Goniometric Diagram
- Radiance
- Incident Surface Radiance
- Exiting Surface Radiance
- Field Radiance or Light Field
- Irradiance from the Environment
- Light meter
- II
- Things to Remember
- Acknowledgments
- A Pinhole Camera Samples Radiance
- Cartesian Diagram
Core Concepts Splines, Bezier Curves Topological Mesh Representations Subdivision, Geometry Processing
Core Concepts Measuring Light Unbiased Integral Estimation Light Transport & Materials
Rasterization Transforms & Projection Texture Mapping Visibility, Shading, Overall Pipeline Intro to Geometry Curves and Surfaces Geometry Processing Ray-Tracing & Acceleration
Monte Carlo Integration Global Illumination & Path Tracing Material Modeling
Measurement system and units for illumination Measure the spatial properties of light • New terms: Radiant flux, intensity, irradiance, radiance Perform lighting calculations in a physically correct manner
• Photons travel in straight lines, represented by rays
Light Emitted From A Source “Radiant Intensity” Light Falling On A Surface “Irradiance” Light Traveling Along A Ray “Radiance”
Definition: The radiant (luminous) intensity is the power per unit solid angle emitted by a point light source. ⌘ d d! W sr (! ) I ⌘ lm sr W d! d sr lm sr = = cd = candela The candela is one of the seven SI base units.
! Will use ! to denote a direction vector (unit length)
http://www.louispoulsen.com/ PH Artichoke Lamps in Rivercenter for the Performing Arts, Georgia
Light Traveling Along A Ray Radiance is the fundamental field quantity that describes the distribution of light in an environment Radiance is the quantity associated with a ray Rendering is all about computing radiance Radiance is invariant along a ray in a vacuum
Equivalent: Incident surface radiance (luminance) is the irradiance per unit solid angle arriving at the surface. dA ✓ ! d! L(p, ! ) = dE (p) d! cos ✓ i.e. it is the light arriving at the surface along a given ray (point on surface and incident direction).
Equivalent: Exiting surface radiance (luminance) is the intensity per unit projected area leaving the surface. dA ✓ ! d! L(p, ! ) = dI (p, ! ) dA cos ✓ e.g. for an area light it is the light emitted along a given ray (point on surface and exit direction). Incident & Exiting Surface Radiance Differ!
Definition: The field radiance (luminance) at a point in space in a given direction is the power per unit solid angle per unit area perpendicular to the direction. dA d! !
Computing flux per unit area on surface, due to incoming light from all directions. dE (p, ! ) = E (p) =
d! Contribution to irradiance from light arriving ! from direction
“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
Radiometry vs photometry: physics vs human response Spatial measures of light: Flux, intensity, irradiance, radiance Pinhole cameras and light field cameras Lighting calculations Integration on sphere / hemisphere Cosine weight: project from hemisphere onto disk Photon counting Radiometric / photometric units
Many thanks to Kayvon Fatahalian, Matt Pharr, Pat Hanrahan, and Steve Marschner for presentation resources. Extra
Photograph pixels measure radiance for rays passing through pinhole in different directions Spherical Gantry
http://www.louispoulsen.com/ Light Fixture Measurements
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A student wants to compare the luminous flux of a lightbulb with that of a 1750-lm lamp. The lightbulb and the lamp illumi-nate a sheet of paper equally. The 1750-lm lamp is 1.25 m away from the sheet of paper; the lightbulb is 1.08 m away.
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For the following problems give calculated answer, sig figs, and/or scientific notation when applicable. 7. What is the illumination of the page of a book that is 2.75 m directly below a source whose intensity is 150 cd?
1. Radiant flux [luminous flux] Radiant flux is a unit to express radiant quantity, while luminous flux shown in brackets [ ] in Table 1-2 and the subhead just above is a unit to represent luminous quantity. (Units'are shown this way in the rest of this chapter.)
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Luminous Flux or Power P or Φ lm Luminous Exitance M M = dΦ dA lm=m2 Illuminance E E = dΦ dA lm=m2 Luminous Intensity I I = dΦ dΩ lm=sr Luminance L L = d2Φ dAcos dΩ lm=m2 Spectral Luminous Efficiency V ( ) Dimensionless Color Matching Functions ¯x( ) y¯( ) z¯( ) Dimensionless Apr. 2014 c C. DiMarzio (Based on Optics for Engineers, CRC ...
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What is the difference between radiant intensity and luminous intensity?
Lumens (abbreviated to lm) are the units of luminous flux. Imagine the flux from a luminaire (the technical name for a light source) to be the sum of the lengths of all the rays of light. Think of flux (in Lumens) as an amorphous blobby flow of energy issuing the luminaire. Luminous intensity (candelas, cd)
