scope:

Aim

The purpose of the TC 1-80 work was to provide guidance to aid the successful implementation of the experimental procedures commonly used to measure spatial brightness. This was done through a review of the procedures and conditions under which these experiments have been carried out.

Spatial Brightness describes a visual sensation to the magnitude of the ambient lighting within an environment, such as a room or lighted street. Generally the ambient lighting creates atmosphere and facilitates larger visual tasks such as safe circulation and visual communication. This brightness percept encompasses the overall sensation based on the response of a large part of the visual field extending beyond the fovea. It may be sensed or perceived while immersed within a space or when a space is observed remotely but fills a large part of the visual field. Spatial brightness does not necessarily relate to the brightness of any individual objects or surfaces in the environment, but may be influenced by the brightness of these individual items (Fotios & Atli, 2012).

Evaluation of spatial brightness is a subjective assessment and experimenters need to be aware of the limitations of such assessments as can be observed through two statements:

Quantitative subjective assessments are almost always biased, sometimes completely misleading.

[Source: Poulton, E.C., British Journal of Psychology, 1977; 68; 409-425]

In the study of perception, I think we get caught up a little in thinking that much has to do with what people see. Sometimes the procedural matter is more about influences on what people say, rather than what they see.

[Source: Niall, K., TC1-80 member, June 2011; feedback on an early draft]