Understanding Light Reflectance Value (LRV) is important to the design, construction, and maintenance of buildings that can be used safely by everyone. LRV is a measure of the percentage of visible light reflected by a surface, weighted for the sensitivity of the human eye.
LRV ranges from 0 to 100. A value of 100 indicates absolute reflectance, while 0 represents no reflectance or total absorption of light. The LRV is used to specify and control contrasts between different materials, fixtures, fittings, and surfaces within the built environment.
Some of the current regulations and codes of practice like BS 8300:2009 and BS8493:2008+A1:2010 established the CIE Y value as the single consistent method. It defined that the visual contrast would be sufficient if the LRV of contrasting surfaces, with illumination greater than 200 lux, differs by a minimum of 20 points. This contrast is calculated using the following formula: (B1 – B2) x 100 / B1, where B1 and B2 are the LRV of the lighter area and darker area, respectively.
The LRV can be obtained using the CIE Y values measured under the illuminant D65 (natural daylight) and 10° observer. This measurement can be conducted easily using a sphere-based spectrophotometer like Konica Minolta Spectrophotometer CM-25d that has a calibration certificate that is traceable to international standards.
The d:8° portable sphere-based CM-25d is ideal for on-site measurements, whether assessing the building as a whole or to test the impact of sun exposure, wear, and cleaning over time.
Besides LRV measurement, the CM-25d, with its high repeatability of σ∆E*ab 0.04 and good inter-instrument agreement of ∆E*ab< 0.12 (average of BCRA 12 Tiles), is also ideal for the measurement of the architectural glass and ceramic tiles.
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