The BLUE COOLING series features C2, C4, C8 and C12 gradation, which refer respectively to a mired shift of -20, -40, -80 and -120.
In other words, as seen in the transmission graph, the BLUE COOLING series reduces orange and reddish light entering the lens, therefore indirectly enhancing blue colors. The lower the mired value, the less orange and red light enters the lens and the stronger the cooling effect.
It is possible to combine various BLUE COOLING filters to achieve different values, which allows photographers to achieve almost any desired color correction.