Critical Lighting

The way that bricks are arranged affects a veneers stability and strength and is referred to as a ‘bond’ or ‘bonding’.

Unless specifically outlined in the contract specifications, imperfections that are only visible under critical light do not indicate defective workmanship. 

Critical lighting occurs when sunlight or an intense artificial light source strikes a wall or other flat surface at a low angle, typically 15° or less. Because of the low angle of the light any small variations or irregularities on the surface cast a relatively large shadow which can highlight imperfections that would not normally be visible under more diffused lighting conditions.
Critical lighting occurs naturally for a short period each day, typically 30–60 minutes in the early morning and late afternoon when the sun is low in the sky.

It is common practice to use high output lighting to accentuate areas requiring attention during the construction phase, but this level of lighting is not suitable for performing a subjective visual inspection of interior surfaces.
More information on critical lighting and its effects is available from:

  • AS/NZS 2589:2007 – Gypsum linings – Application and finishing (particularly Appendix C)
  • AWCIANZ Trade Guidelines and Information Booklet Oct 2012 (www.awci.org.au/national-publications/ trade-guidelines-information-booklet )
  • AWCIANZ Insight Newsletter: Critical light August

Diffuse light is light that is scattered, causing it to fall on the crop from all sides. The light is evenly distributed, leaving no sharp shadows. Diffuse light arises when direct light is scattered naturally (e.g. by clouds) or with artificial means (e.g. a diffuse coating).
Direct light is a light where no obstacle is between the light source and the subject. The light rays all go in the same direction and are completely rectilinear from their point of departure to their destination.