This example shows the subtle and complex influences of lighting component
colors and intensities to the rendered effect.  A grid of spheres is drawn,
with the material colors changing across the grid.  From left to right, the
diffuse material color changes from black (non-reflective) to white (fully-
reflective).  From bottom to top, the specular material color changes from
black to white.  Thus, in a single image, the effect of changing material
diffuse and ambient colors can be seen.  The scene is lit by a single point
light.  For instructional reasons, the ambient, diffuse and specular 
components are each a different color.  The light (represented by a plus
sign) may be moved in three dimensions, to explore the geometric effects of
the lighting.  Also, the ambient, diffuse and specular intensities of the
light may be adjusted (or even completely cleared) to see a single 
component's effect.  Finally, the specular surface material exponent may be
changed, so that the changes to the size of the highlight may be explored

The key commands are:

i, k - translate light in x
j, l - translate light in y
y, h - translate light in depth
q, a - increase, decrease light ambient intensity (red)
w, s - increase, decrease light diffuse intensity (green)
e, d - increase, decrease light specular intensity (white)
r, f - increase, decrease specular shininess (exponent)
Space - reset transforms and lighting values
