The BYK-Gardner color-guide and spectro-guide contain many common and useful color indices. One can change the instrument to most of the widely used color systems: CIE, Lab (hunter), Spectrum, XYZ, Yxy, FMC2 and others. You can also change the instrument to a number of different indices to measure color difference, whiteness, yellowness, opacity and strength. But nowhere in these lists are any indications of the LRV of the color you are measuring.
What is the LRV and why is it important? There are several ASTM specifications that deal with the LRV, also commonly known as the Light Reflectance Value or Luminous Reflectance Factor. ASTM C 609 discusses the LRV of ceramic tiles and ASTM E 1477 deals with the LRV of Ceiling tiles. There are even Transportation and Building Safety codes requiring LRV values and differences in LRV values for signage near emergency exits, both in buildings and on airplanes.
So, how does one obtain the LRV value of a paint color? Many paint companies actually post the LRV value of a color right on the fandeck of colors. So if the requirement for the background color of a sign in an emergency exit is a minimum of 70, it’s quite easy to pick a color. However, if the LRV value isn’t there it is easily measured with the spectro-guide Sphere. This is quite important. The instrument taking the measurement must be a d/8 Sphere.
To set up the spectro-guide to measure the LRV, move to the Option menu at the top of the screen. Under Option, move down to Color Sys. Move to the right and select either XYZ or Yxy for the color system. Push the operate button to select this color system. Then under Option again, move down to Illum/Obs and select D65/10° or F2/10°. The system is not set up to supply the LRV value. The LRV is nothing more complicated than the Y value (capital Y, not the small y in the Yxy system).
Safety signs, in accordance with the Americans with Disabilities Act, are designed so that there is at least a 70 unit difference in LRV between the background color and the text. Colors, even colors which have a very high contrast between them, do not stand out well against each other if the LRV is too close.
As an industry ‘rule of thumb’, a 70% Light Reflectance Value (LRV) contrast between sign text and
background colors is an ideal guideline to follow when evaluating color and finish options. Most major paint manufacturers include LRV values for their colors in their swatch books. These values can be used in the manual calculation below.
Contrast = ( B1 – B2 ) x 100 / B1
B1 = light reflectance value (LRV) of lighter area
B2 = light reflectance value (LRV) of darker area
Experience has shown that the 70% figure is not a magic number. Contrasts of a few percentage points below the recommended figure, depending on the colors chosen, can often yield legible results.
Jim Roberts is a Technical Support Manager at BYK-Gardner USA, Columbia, MD.
For more information on BYK-Gardner’s spectro-guide instruments, please click here.
To watch how to change your color system on your spectro-guide, click on the video below: