The visible light band ranges from 400 – 700 nanometers. Within this band, colors occur in the sequence observed in the rainbow, ranging from violet, to blue, green, yellow, orange and red. Each wavelength in the visible light band causes a particular sensation of color. As shown in Figure 1 and Graph 1, solar radiation is most intense in the visible light band. This band is also the area where the human eye is most sensitive to radiation. However, the eye is not equally sensitive to light emitted at all wavelengths; it is most sensitive to the light in the yellow and green areas of the spectrum.
When a light beam strikes a material, some light is transmitted, some reflected, and the rest is absorbed. Light transmission depends on the reflectance at both surfaces of the material and the absorption of light into the material. Colorless ACRYLITE® acrylic sheets typically absorb less than 0.5% of visible light per inch of thickness. However, some light is reflected at both surfaces. A beam of light striking a smooth ACRYLITE® sheet perpendicular to the surface (at 0º angle of incidence) will lose approximately 4% of its light at each surface due to reflection, resulting in a total loss of 8%. Therefore, the overall light transmission will be approximately 92%. If light rays strike the sheet at angles greater than 30 degrees from the vertical, the surface reflectance will be greater than 4% and, thus, the overall transmission will be smaller. For example, when light falls on colorless ACRYLITE® cast or ACRYLITE® premium acrylic sheet from all angles, as from a sky of uniform brightness, the transmission factor will be approximately 85%.