Light reflectance value (LRV) is the total quantity of visible and useable light reflected by a surface in all directions and at all wavelengths when illuminated by a light source (as defined in British Standard BS 8300:2001/A1:2005). The LRV scale expressed as a percentage ranges from 0, which is the darkest or least reflective, to 100, which is the lightest or most reflective – the LRV of the whitest white is approximately 85%, and the LRV of darkest black is approximately 5%.
E2/AS1 requires an LRV of 40% or higher for EIFS systems and fibre-cement sheets that have a flush plastered system. There are no requirements for stucco, but NZS 4251.1:2007 Solid plastering – Cement plasters for walls, ceilings and soffits recommends lighter colours to reduce the likelihood of cracking.
For timber or fibre-cement weatherboards and flat sheet materials, manufacturers may have specific LRV requirements for coatings applied to them, and some paint suppliers may have LRV requirements depending on the material the coating is applied to.
Timber generally requires an LRV of 40% or greater to minimise the amount of heat build-up in the timber and the resultant thermal movement.
Coating manufacturers have developed darker-coloured coatings that have a better ability to reflect and allow a darker colour to be used than would otherwise be possible.
Summarised from BRANZ Guideline, February 2014.