Demo 2 - Adobe Atmosphere. Modeling Reflections

When light energy reaches a surface, some is absorbed (turned into heat) and some is reflected. How much and what color is reflected depends on the color and texture of the surface. The rule is, "The angle of incidence (incoming angle) equals the angle of reflection (outgoing angle)". In other words, like billiard ball angles, but without any spin.

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The demo below has two identical small test environments, except the sides are removed from the left one and the bottom is black, so no reflections can hit the square vertical column.

What to do, notice and investigate

1. Which environment puts the most light onto all sides of its square upright test column? Why?
2. Does light reach the back side of both columns?
3. Are there more than 5 reflection paths reaching the back side of the column in the right environment (think billiard balls!)?
4. If the walls and floor of the right environment were painted black, would the result be about the same as the left one?
   

1. Which environment puts the most illumination onto its column?

Obviously the walls of the right hand environment reflect more light onto the square column than reaches the square column in the left hand environment. The white "mirror" in the right environment reflects the most. Multiple reflections paths even reach the back and sides of the column, which the light source cannot light directly (Radiosity in action ).

2. Does light reach the back side of both columns?

No, without the walls and white reflector to reflect the light, no light illuminates the back side of the column in the left environment.

3. Are there more than 5 reflection paths...?

Yes, since the light can reflect off the floor as well as the walls, there are many more than 5 ways for light to reach the sides or back of the square column in the right hand environment. Of course, the paths that have the fewest reflections (and absorptions) give the most light, so the longest and most indirect paths don't provide much light and can be ignored. Even Atmosphere doesn't have to calculate every possible reflection.

4. If the right environment walls were black, would it look like the left?

Yep, for all practical purposes, painting a wall black stops light reflections just as well as having no wall, since black (the absence of color), in the presence of a nearby light source, only happens when all light is being absorbed.

1. The angle of incidence equals the angle of reflection - just like billiard balls.
2. The lighter in color a reflector is the more light it reflects.