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Jun 7, 2024 · Luminous flux is a fundamental concept in optics representing the total amount of visible light emitted from a source in all directions. It measures the total quantity of light energy emitted per unit time, illuminating the surroundings and affecting the observer’s brightness perception.
A 150 watt light bulb emits a luminous flux of 2275 lm. Find the resulting luminance at each distance shown in the table below. Create a graph of illuminance vs. distance for this bulb.
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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 illuminate 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.
- 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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The luminous flux accounts for the sensitivity of the eye by weighting the power at each wavelength with the luminosity function, which represents the eye's response to different wavelengths. The luminous flux is a weighted sum of the power at all wavelengths in the visible band.
May 25, 2024 · Mathematically, luminance is defined as the amount of luminous flux per unit projected area per unit solid angle. It is denoted by the symbol “L”. The formula for luminance is derived from the ratio of luminous flux to the product of projected area and solid angle. This core formula is expressed as follows:
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Jun 7, 2024 · Mathematically, illuminance (E) is expressed as the ratio of luminous flux (Φ) incident onto a surface to the surface area (A) receiving that flux. This core formula can be articulated as follows: Where: – ∅ is luminous flux (in lumens or lm) – A is the surface area (in square meters or m²).
