Lesson 7 – Light-Matter Interactions

When light interacts with a shiny, smooth optical material, most either specularly reflects or transmits. However, even at polished optical surfaces light may also scatter or be absorbed. Most common, non-optical surfaces scatter light, and this is what allows them to be seen. Scattering may occur in the forward direction, transmitting into the same general direction as the initial beam of light, or in the reverse direction, reflecting back toward the light’s source. This reduces the amount of light that is specularly reflected or transmitted. Some materials reduce the amount of light transmitted by absorbing it, or changing it to another type of energy like heat.

Considering all of this, when light interacts with any material, it must either reflect, transmit, scatter, or be absorbed. When accounting for all these interaction phenomena, conservation of energy is invoked—the quantity of light reflected plus the light transmitted plus the light scattered plus the light absorbed must equal all of the light initially incident.