A measurement of the amount of color shift that objects undergo when lighted by a light source as compared with the color of those same objects when seen under a reference light source of comparable color temperature. CRI values generally range from 0 to 100. The law that the illuminance on any surface varies as the cosine of the angle of incidence. The process by which the retina becomes adapted to a luminance of less than 0.01 footlamberts. The ratio of daylight illumination at a given point on a given plane due to the light received directly or indirectly from a sky of assumed or known luminance distribution, to the illumination on a horizontal plane due to an unobstructed hemisphere of this sky, expressed as a percentage.
Direct sunlight is excluded for both values of illumination.
The daylight factor is the sum of the sky component, the external reflected component, and the internal reflected component. The interior plane is usually horizontal. If the sky condition is the C.I.E. standard overcast condition, then the DF will remain constant, regardless of absolute exterior illuminance. If used in conjunction with other than standard overcast conditions, the sky conditions should be specified. Those surfaces and glazing that redistribute some of the incident flux by scattering in all directions.