Sun and SkyDiffuse illuminance (Evd) also called Skylight - Solar Radiation reaches the Earth as a Result of Scattering in the AtmosphereDirect illuminance (Evs) also called sunlight - Solar Radiation reaches the Earth’s Surface as Parallel Rays, directly from the Sun’s Disc, after Selective Attenuation by the AtmosphereGlobal Illuminance (Evg) Evg = Evd + Evs
CIE Standard Overcast SkyCompletely Overcast SkySky being 3 times Brighter Overheadthan Horizon
Daylight Factor (DF) Illuminance received at a Point Indoors, expressed as a Percentage of Evd from an UNOBSTRUCTED sky. Containing Sky Component (SC), Externally Reflected Component (ERC) and the Internally Reflected Component (IRC)
Vertical Daylight Factor (VDF)Illuminance received at a Point on aVERTICAL OUTDOOR Surface, expressedas a Percentage of Evd from anUNOBSTRUCTED sky. Containing SC andERC.Applied in PNAP APP-130 Lighting andVentilation Requirements –Performance-based Approach
Daylight Glare Index (DGI) Glare from Windows can arise from Excessive Contrast between the Luminance of the Visible Sky and the Luminance of the Internal Surfaces within the Field of View.
Daylight Autonomy“The % of Aggregate Floor Area of RegularlyOccupied Spaces which achieves a minimumhighly Illuminance value of 300 lux at TaskLevel for at least 50% of the hours between8am to 6pm, Local Clock Time, after accountingfor Typical Weather Conditions, ExteriorObstructions, Attached Furniture Systems andafter Blinds have been operated Hourly toblock Direct Sun predicted to enter the Spacethat would fall on more than 2% of theCalculation Grid.” LEED 2012 Draft 3
Global IlluminationMaxwell’s Electromagneticwave equationRadiosityRay-tracing
Maxwell’s Electromagnetic wave equation Treating Light as EM Wave Could model the behaviours (Reflection, Refraction, Diffraction, Interference) of Light Uncommon neither in Daylighting Research or Design
RadiosityOriginally developed for Energy Calculation(Energy Balance for a set of Surfacesexchanging Radiant Energy)Surfaces must be subdivided into FiniteElementsAll elements are assumed to be PerfectlyDiffuseView IndependentPre-eminence of major light sources
RaytracingDetermine the Visibility of Surfacesby Tracing Imaginary Rays of Lightfrom Viewer’s eye.Account for every Optical Phenomenonthat can Analytically expressed byPhysical EquationCan consider specular material
Sky ModelA simple program gensky is includedin Radiance. This program can createa sky description file for thefollowing sky:CIE overcast skyUniform skyCIE clear sky (1973)CIE clear turbid sky
CIE Standard General Skies 5 Clear, 5 Intermediate and 5 Overcast Sky Types Any Standard Sky can be considered as combining the Gradation function φ(Z) and Indicatrix Function f(χ)
Gradation FunctionThe Standard Gradation Equationrelates Sky Luminance to the AngularDistance from the Zenith
Scattering IndicatrixThe Relative Scattering IndicatrixFunction models Sky Luminance withAngular Distance from the Sun.
CIE Standard General Skies No Type of sky Overcast with the steep gradation and azimuthal 1 uniform Overcast with a steep gradation and slight brightening 2 toward sun, Overcast moderately gradated, azimuthal uniformity 3 Overcast moderately gradated and slightly brightening 4 toward sun Overcast or cloudy with overall uniformity 5
CIE Standard General Skies No Type of sky Partly cloudy with a uniform gradation and slight 6 brightening toward sun Partly cloudy with a brighter circumsolar effect and 7 uniform gradation Partly cloudy, rather uniform with a clear solar corona 8 Partly cloudy with a shaded sun position 9 Partly cloudy with brighter circumsolar effect 10
CIE Standard General Skies No Type of sky White – blue sky with a clear solar corona 11 Very clear / unturbid with a clear solar corona 12 Cloudless polluted with a broader solar corona 13 Cloudless turbid with a broader solar corona 14 White – blue sky, turbid with a wide solar corona 15 effect
Ambient Divisions (-ad) andAmbient Super-samples (-as) To reduce the Errors in Monte Carlo Calculation of Indirect Illuminance Error reduce in a Inversely Proportional to the Square Root of this Value Addition Sampling will be done if -ad shows a significant Change Doubling this value doubles the Rendering Time
Ambient Accuracy (-aa) and Ambient Resolution (-ar) -aa controls the Error from Indirect Illuminance Calculation -ar determines the Maximum Density of Ambient Values used in Interpolation. The Maximum Ambient Value Density is the Scene Size times -aa divided by -ar. Doubling these Two Values quadruples the Time for Rendering
Common Misunderstandings in Global Illumination
Use Large Surface as Possible YES.... but also NO Recall the Definitions of -aa and -ar The -ar Setting is proportional to Minimum/Average Size An Oversize Surface in the Scene, -ar need to be increased. And Sometimes it requires a very large -ar.
Using a single Surface for Multiple Surfaces Sure!
Using a single Surface for Multiple Surfaces How about these?
ConclusionsReview Major Simulation Technique involvedin Global IlluminanceIntroduces RADIANCE System includes theinputs and outputsReview the Parameters and Items affectingthe Accurcy of simulationIntroduces two of the Major Misunderstandingin Global Illumination