|
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!
|
