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Natural Science Forum / Physics / General Physics / August 2007Radiance/Irradiance - Maya
Hi, Can someone please give me a basic (working) , non mathematical, definition for radiance and irradiance? I have been using Wiki/Google but it is difficult for me to tell when to use one term and when to use the other. I need this for an artistic graphical application not something scientific or mathematical. Here is what I came up with: Radiance - amount of light emitted from a surface Irradiance - amount of light incident on a surface Thanks, Ron : Hi, : Can someone please give me a basic (working) , non mathematical, [quoted text clipped - 7 lines] : Radiance - amount of light emitted from a surface : Irradiance - amount of light incident on a surface That's it exactly. The sun radiates and irradiates the planets, including Earth. A radar beam radiates and irradiates a plane. Thanks Androcles > Hi, > Can someone please give me a basic (working) , non mathematical, [quoted text clipped - 10 lines] > Thanks, > Ron Photons/area, energy/area. Spectral distribution may matter. Depends what you need.  SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > Hi, > Can someone please give me a basic (working) , non mathematical, [quoted text clipped - 7 lines] > Radiance - amount of light emitted from a surface > Irradiance - amount of light incident on a surface Ahhhh... Radiometry. That most dismal science. "Radiance" is one of the more complicated quantities, so I'll build up to it. Irradiance has units of watts/area, and refers to the amount of power either incident onto, exiting from, or passing through a surface. Irradiance is sometimes called "Incidance" or "Exitance" in conjuction with the first two meanings. Irradiance does not tell you how the flux is distributed in direction. Intensity has units of watts/solid angle. It tells you into what direction the power is being radiated. Combine the two, and you have "radiance". It has units of W/(area*solid angle), and not only tells you where the radiation is going, but how much is being emitted from an extended surface. Note that the area is actually the *projected area*, becasue radiance is tied into the direction that radiation is emitted. Radiance is the fundamental radiometric quantity. It is invariant for any optical system. The best book for all of this is William Wolfe's "Introduction to Radiometry" (SPIE Press TT29) SignatureAndrew Resnick, Ph.D. Department of Physiology and Biophysics Case Western Reserve University > ronvi...@gmail.com wrote: > > Hi, [quoted text clipped - 37 lines] > Department of Physiology and Biophysics > Case Western Reserve University Hi Dr. Resnick That's the kind of answer that was confusing me before. I liked it better when Androcles was telling me how right I was. When you write "or passing through a surface" do you mean that it is exiting the interface? Can something be incident and still pass through? Unfortunately I do not have the aptitude for the Wolfe book you mentioned but I only need to be able to understand it well enough to build illumination maps with Maya (my 3D app.). Thank you, Ron <snip> >>Radiance is the fundamental radiometric quantity. It is invariant for >>any optical system. [quoted text clipped - 12 lines] > "or passing through a surface" do you mean that it is exiting the > interface? Can something be incident and still pass through? Irradiance is a power density. Perhaps it's easier to think of it as power incident onto a surface (hence, Incidance), or exiting from a surface (Exitance). But, one can think of the power passing through a plane even if no material surface is present. They are all the same concept; why they have different names is a different issue. Radiometry is the study of the flow of electromagnetic energy- what direction it propogates and how it is absorbed/scattered (and the directions it is scattered). I can illuminate a surface with 100 MW/mm^2, some will be absorbed, some will be scattered. I can take the surface away, there is still an irradiance of 100 MW/mm^2 passing through the plane where the surface used to be. > Unfortunately I do not have the aptitude for the Wolfe book you > mentioned but I only need to be able to understand it well enough to > build illumination maps with Maya (my 3D app.). Wolfe is a surprisngly easy read, and it's an excellent reference. I don't know what Maya does. There's a few good web resources you may like; search for "bidirectional reflectance distribution function". Check out gaming sites for ideas also. SignatureAndrew Resnick, Ph.D. Department of Physiology and Biophysics Case Western Reserve University > But, one can think of the power passing through a > plane even if no material surface is present. > I can take the > surface away, there is still an irradiance of 100 MW/mm^2 passing > through the plane where the surface used to be. > -- > Andrew Resnick, Ph.D. > Department of Physiology and Biophysics > Case Western Reserve University Got it. Thank you. Thanks also for the search BRDF tip. It turns out to be very important, as well as the more general BSSRDF used for simulating subsurface scattering. http://graphics.ucsd.edu/~henrik/ http://graphics.ucsd.edu/~henrik/papers/bssrdf/ Here is what Maya does - besides gaming Industrial Light & Magic (ILM) was the main visual effects house for Pirates of the Caribbean: At World's End. ILM used Maya and Flame as part of its proprietary SABRE visual effects system to create computer- generated characters and maelstrom sequence. Transformers - ILM used Maya and Inferno as part of its proprietary SABRE visual effects system to complete 460 shots for the film. Maya was used for all character animation, including the challenging opening sequence in which a robot attacks an American military base in the Middle East. The robot's bones were created using Maya and imported into Inferno, and were animated and combined with flying and burning debris. Fantastic Four: Rise of the Silver Surfer - The Orphanage completed approximately 120 shots on the film, with the majority of shots involving Maya 3D animation software. Surf's Up, from Sony Pictures Imageworks. The wizards at Sony Pictures Imageworks used Autodesk Lustre color grading system for the film's final grade. Also, a combination of software was used to create the final water animation, with much of it completed using Maya. Penelope is the story of pig-nosed Penelope Wilhern (Christina Ricci) and her family's secret curse. Double Negative turned to Maya to create the complicated computer-generated tree that helps tell the tale in the film's opening. Evan Almighty: Rhythm + Hues used Autodesk Maya to create computer- generated characters and CafeFX used Maya to model and animate sixty CG salt-water tropical fish |
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