Raout-in: Color rendering of objects in a daylit room viewed from outdoors

This paper addresses the definition of a new criterion Raout-in to evaluate the color rendering of objects in a room viewed by an observer who is outdoors. This is not only relevant when outdoor observers are viewing persons in the room. It is also frequently taken into account when the color of internal solar-control or glare protection systems is selected so that they have a pleasing appearance for both indoor and outdoor observers. The relation of the new criterion to the general color rendering index Ra as applied for daylight transmitted through glazing is discussed and several solar control systems are assessed with respect to Ra and Raout-in. Both color rendering indices are based on an evaluation of the color rendering of eight moderately saturated test colors illuminated with the reference illuminant D65 and the illuminant under consideration (e.g. the same illuminant transmitted through a spectrally selective solar-control glazing). A discussion about an extension of the range of test colors by addition of strongly saturated test colors is also included in the paper.