Aperture-based daylight modelling: Introducing the ‘View Lumen’

This paper presents a new way to determine measures of view at the building aperture. It introduces the concept of the view lumen – this is the illumination effect received at the building aperture from a visible external entity (e.g. ground, sky, obstruction, etc.) which is made self-luminous for this purpose. The paper describes the fundamental principle behind the view lumen, and gives some preliminary illustrations of the technique to show its potential. The examples employ the British Standard framework to define categories of view. That is, three layers named upper, middle and lower comprising, respectively, sky, natural or man-made objects (e.g. buildings) and ground. The proposal is an extension of the recently introduced sunlight beam index