Photometric accuracy (absorbance) is measured by shining a light beam from the spectrophotometer through the inserted filter. An absorbance value (Abs) can be deduced from the light attenuation caused by the filter. The light attenuation produced by the filter gives the absorbance value (Abs). A reference material for checking the photometric accuracy ideally has wide flat scan lines.

Hellma Analytics neutral density glass filters are made from filter materials produced by Schott AG, which were selected on account of their homogeneity and stability. Thanks to a relatively constant transmittance within the wavelength range of 405 nm to 800 nm, they have been used to check photometric accuracy and linearity in the visible wavelength range (> 405 nm) for decades.

You can specify any 5 wavelengths between 405-890nm as calibration points, and there is no extra cost for this service.