Our neutral density filter sets are based on and traceable to the NIST sets SRM 930e and SRM 1930. These sets are used to test the photometric scale in both Transmission and Absorbance in the visible range. The filters are made from Schott NG-type glass which blocks known transmission and absorbance values. We calibrate the glass type and thickness of the filters to produce the transmission and absorbance values. The approximate values are shown in the chart below. Each NIST traceable filter set is individually tested and certified to its transmission and absorbance values and the confidence limits of each reading.

The neutral density filters are mounted in a black anodized aluminum holder, 12.5mm x 12.5mm x 45mm high. The dimensions are the same as a standard instrument cell holder and will work with all standard spectrophotometers. The filters have been shown to be effective in instruments with an effective bandwidth of 2.2n to 6.5 nm.

Set your spectrophotometer in either absorbance or transmission with a wavelength of 440.0nm. Using the empty filter holder (blank), zero the instrument. Insert each filter in turn and note the value. Set your instrument to each successive wavelength and repeat the procedure. The value that you read should be close to the measured certificate value listed for that filter. Using the readings of the filters from your instrument, you can assure the photometric accuracy of your instrument is within the operating specifications from your instrument's manufacturer.

Repeat the tests at a fixed period of time. If you note any discrepancy in the readings, call your service technician and they can use the data that you have collected from using the filters to diagnose and correct any problems with your instrument.