The Monte Carlo simulation process proceeds as follows. Individual photons of daylight are emitted from a plane outside the room. Each is traced from birth to death, through possibly many intermediate interactions (reflections or transmissions) with surfaces. An event proceeds as follows. First, all photons are traced to their surface of interaction. Next, the interaction occurs, resulting in the photons being absorbed (death) whence tracing ceases, reflected or transmitted. If reflected or transmitted, the outgoing direction is determined. The tracing then recommences with the next event.
The objective of each complete simulation is to compute the lluminance of the work surface. A completely transmitting ``work'' surface at a height of 3 ft. (1 meter) above the floor is subdivided into a grid. The number of photons which pass through each subdivision of the work surface are tallied. A series of simulations are performed, varying the geometry and the material properties, to optimize versus cost the parameters of the design.
In the accompanying video, we illustrate this process by displaying photons as they enter the geometry of Figure 22 and interact with interior surfaces. There are multiple views of the process, from the rear of the room, and various side perspectives. Photons which are emitted from the exterior ``solar'' surface are initially colored yellow. If they succeed in passing through the windows into the room, their color is changed to red for those which are transmitted through the upper light duct window or green for those which are transmitted through the lower view window.
In this particular example, there are mini-blinds inside the view window, which serve to reflect the strong sunlight up onto the bottom of the light shelf, which is a diffuse white surface. This diffuses the strong daylight and distributes it to the front one-third of the room. A close-up view of this process is also shown on the video.
The video has been very effective in illustrating the process to non-technical audiences. It has received particular attention from the Architectural community.
Photon animation - mpeg.
(See exercise 7.)