Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Absorptance (formerly Absorption Factor) Ratio of the absorbed radiant or luminous flux to the incident flux. Absorption Conversion of radiant energy to a different form of energy by interaction with matter. AC (Alternating Current) Current which passes from the generator in one direction and then the other, alternately. Accommodation Focal adjustment of the eye, generally spontaneous, made for the purpose of obtaining maximum visual acuity at various distances. Adaptation 1. The process by which the state of the visual system is modified according to the luminances or the color stimuli presented to it. 2. The final state of the process. Back to top Angle of tilt see Tilt, angle of Arc Intense luminous discharge formed by the passage of electric current across a space between electrodes. Arc discharge (in a gas or vapor) Electric discharge characterized by a cathode fall that is small compared with that in a glow discharge. Average illuminance (Eav) Over a surface, Illuminance averaged over the specified surface. Average luminance coefficient (Q0) A measure for the lightness of a road surface being defined as the value of the luminance coefficient q averaged over a specified solid angle of light incidence.