Modify the code obtained in Exercise 3 to perform a simulation of daylighting. This modification is accomplished in a series of steps as follows.
(a) First, photons must be emitted from only one surface (choose a vertical
surface - say the left side), a ``solar'' surface which simulates photons
coming from the sun. They can be emitted in a constant direction, and
should be emitted with a positive 
and a negative 
. Photons need
not be emitted from any other surfaces. Also, if you implement a non-zero
reflectance (see part (c), then all photons which get back to the
``solar'' surface should not be reflected (i.e. should be absorbed).
(b) Second, the photons from the ``solar'' surface must be traced and those
which pass through the ``work'' surface (corresponding to a typical height
of a desk) must be tallied. It is useful to capture the flux of these
photons by partitioning the work surface into a grid (10 grids in the X
direction is a good number). This work surface is a non-interacting
surface, used only for tallying photons which pass through it. It is
convenient to define this surface to be a plane at 
in the
geometry given.
(c) Finally, you may wish to make the surfaces reflecting. Choosing a diffuse reflectance of 0.7 is typical of a surface painted flat white, yielding an absorptance of 0.3.
