Simply put, colour and texture equally affect the amount of light reflected by any surface. The more light reflected, the higher the LRV, the less light reflected, the lower the LRV. In the case of Dryvit finishes, for example, a white Sandblast® will have a high LRV, while a dark - coloured Quarzputz® will have a lower one. The LRV is generally measured using a spectrophotometer, and is expressed as a number without units. But this LRV number is indirectly related to the percentage of light reflected.
Architects may specify a certain LRV range in an attempt to provide a distinct colour range for a project containing multiple units. For example, in Tucson, Arizona, all homes must be constructed with finishes within a certain LRV range, to ensure a given earth-toned colour group is maintained.
LRV can also affect energy consumption of the building - for example, in a hot climate a building will absorb less heat from the sun if it has a lighter and smoother finish, rather than a dark and coarsely textured one. Conversely, in a cold climate a building may be kept warmer by specifying a colour and texture with a low LRV.
The basis for determining the LRV value is the ASTM (AMERICAN SOCIETY FOR TESTING AND MATERIALS) standard E 1477 - 98a titled: "Standard Test Method for Luminous Reflectance Factor of Acoustical Materials by Use of Integrating-Sphere Reflectometers"
It's a fairly simple test method where "Test specimens are measured for (total) luminous reflectance factor by standard colour-measurement techniques using a spectrophotometer, tristimulus (filter) colourimeter, or other reflectometer having a hemispherical optical measuring system, such as an integrating sphere. The specular component is included to provide the total reflectance factor condition. The instrument standard is referenced to the perfect reflecting diffuser. Luminous reflectance factor is calculated as CIE tristimulus value Y for the CIE 1964 (10°) standard observer and CIE standard illuminant D 65 (daylight) or F 2 (cool white fluorescent).
We can easily measure the Y value and therefore obtain LRV values for any of our finishes.
So in short: LRV value = Y value
Please remember: LRV values can differ between different finishes and supply plants!
Please contact your regional Dryvit plant Colourist
Make sure you have the following information available:
Acknowledgements: Information offered in this datasheet has been obtained from Datacolor.com, Color Learning: From The Experts.