Display++ neutral density filter set and mounting brackets for scotopic vision tests. Scotopic vision testing requires attenuation of the overall light emitted from the Display++. This is achieved by using a set of calibrated Neutral Density (ND) filters. At scotopic light levels, the peak white value is set at 1 cd.m^-2 and the set of calibrated ND filters attenuate that peak level to about 0.0005, still with a black level which is 3 log units lower (assuming the LCD contrast ratio is > 1000:1). So, peak (R=G=B=1) = 0.0005 cd.m^-2, “black” (R=G=B=0) = 0.0005/1000 = 0.0000005 cd.m^-2. The ND filters are customized, factory calibrated and provided with the necessary brackets to mount on the existing Display++ frame.