PVC or Paint Value Calculation is a method used to determine the ratio of paint's resistance to fading. It is expressed as a percentage and is determined by measuring the amount of light that passes through a sample of paint after it has been exposed to a specified number of cycles of ultraviolet light. The lower the PVC, the greater a paint's resistance to fading.
To calculate PVC, you will need:
-A piece of white paper
-A black Sharpie
-A calculator
-Exterior latex paint in desired colors
first take your exterior latex paint and pour out enough onto the white paper so that when you make a 1 inch circle with the black Sharpie, there is still some wet paint left inside the circle. This will be your test patch. Let this dry completely for at least 24 hours before continuing. Once it is dry, measure the diameter of your circle with the black Sharpie still intact. This will be X1. Now use an X-Acto knife or something similar to cut out your one inch test patch from the center of your dried paint sample while being very careful not to damage any surrounding areas. Set this aside for now..
Now we need to determine how much light will be passing through our one inch test patch which we just cut out. In order to do this we will need to find what is called the %Transmittance(T)of our UV light source using equation T=I/I0 where I0is the original intensity(in lux or footcandles)and I is the measured intensity after exposure (lux or footcandles). A standard 100 watt incandescent bulb has an I0of 17000 lux and an average household fluorescent tube has an I0of 700 lux so we can easily plug these values into our equation making sure all units cancel out leaving only a numerical value for T . From here we can convert our Tvalue into what is called haze units(HU)or % haze using equation HU=100%-%T*100%. With all that being said, lets say we are working under conditions where our fluorescent tube has an initial intensity or I0of 700 lux and after 10 minutes exposed to our UV source its measured intensity or I drops down too 400 lux giving us a transmittance(T)of 57%. We would then plug these values into our equation which would give us a haze unit value or HU=