Period Costs. Period costs are expenses that are easier to attribute to times and accounting periods than actual production processes or finished goods. Typically, managerial accountant want to classify expenses in categories that can improve operations. Manufactures tend to focus on functional classifications.
The amber color of these impact-resistant polycarbonate lenses block short-wavelength blue light and 100% of ultraviolet (UV) light, thus providing additional protection against cataract formation and the development of macular degeneration, while increasing contrast on both sunny and bright hazy days.
Since blue light seems to be particularly harmful (it carries the most energy of all the visible wavelengths), choose a lens color that blocks a lot of blue. Amber or gray tint will work well. Do not choose lenses that transmit blue light. You can see what color light a lens will let through by holding the glasses up to a light and looking at the color of the light coming through the side that would face your eyes.