Radiance change with light distance

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Discussion Overview

The discussion revolves around the behavior of radiance in the context of the rendering equation and Monte Carlo integration, particularly focusing on the implications of distance from a point light source and how it affects illumination of objects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that since radiance does not change with distance, a point light source could theoretically illuminate objects from an infinite distance away.
  • Another participant questions this interpretation, noting that light is not physically composed of rays and expressing uncertainty about the claim.
  • A later reply indicates that while rays can be modeled as individual photons for intuition, the energy associated with each ray in the simulation is likely much greater than that of an actual photon.
  • Concerns are raised about the limitations of the model, particularly regarding the computational cost of tracing more rays with less energy and the physical accuracy of modeling reflections over large distances.
  • One participant emphasizes that the first limitation is significant, while the second is less of a concern for practical applications.

Areas of Agreement / Disagreement

Participants express differing views on the implications of radiance remaining constant with distance, with no consensus reached on whether a point light source can illuminate objects from an infinite distance.

Contextual Notes

The discussion highlights limitations related to the computational cost of ray tracing and the physical accuracy of modeling reflections, which remain unresolved.

Gadersd
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I am trying to solve the rendering equation with monte carlo integration. I gather all of the incoming radiance from light sources and plug it into the rendering equation. A reference I am using said that radiance does not change with distance. Does this mean that a point light source will illuminate objects from a infinite distance away since the radiance does not change?
 
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Not sure. Can you provide a link to your reference?
 
I can't be sure, but it appears to say that whatever quantity of light you have associated with a ray will stay with that ray. I wouldn't say that a point source can illuminate an object an infinite distance away, since light is not physically composed of rays.
 
In this modelling scenario you are modelling the path of individual rays which may as well be regarded as individual photons for the purpose of intuition, although the amount of energy associated with each ray is likely to be much greater than an actual photon.

Yes the ray will travel infinitely if running the simulation does not introduce an interaction with another object. But what probability is associated with this outcome in your scenario?

The model appears limited by the quantity of light that can be associated with a ray, and also by the physical accuracy of modelling reflections between ideal flat surfaces separated by large distances.

The first limitation is due to the increase in computational cost of tracing more rays, each having less energy associated with it (as ray energy approaches photon energy resolution is improved). The second limitation is due to measuring and encoding accurate curvature.

The first limitation is obvious and tangible. The second is barely of concern for basically all pracital applications.
 
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