National Physical Laboratory

Neutral Density & Transmitted Colour Filters

NPL offers a range of transmittance standards for use as calibration standards for spectrophotometers.

Transmittance Standards

Neutral Density Filters

NPL can provide calibrated neutral density filters.The filters can be provided in a variety of sizes, typically mounted in frames for use in 10 mm path length cuvette holders. These cuvette-sized filters have a working aperture of 24 mm x 8 mm and are those that are typically used to certify spectrophotometers. Other sizes such as 50 mm square or 25 mm in diameter can also be provided.

Both glass and metal-on-silica filter types are available. The metal-on-silica filters consist of a silica substrate coated on one side with a nickel chromium alloy. The advantage of the metal-on-silica filters is that they can also be used in the UV.

A wide range of optical density values can be provided, with typical values shown below. Other optical density values are available on request.

Nominal optical density

Nominal Transmittance
(T%)

0.04
0.22
0.5
1
1.5
2
2.5
3
4
5

90
60
30
10
3
1
0.3
0.1
0.01
0.001

Transmitted Colour Filters

NPL can also provide red, yellow and blue glass transmittance standards. For each colour, 9 transmittance levels are available, ranging from approximately 3% to 85%. The standards have a working aperture of are 19 x 9 mm and are compatible with 10 mm path length cuvette holders.

Transmittance data are usually supplied in 5 nm intervals from 380 nm to 780 nm. Colorimetric data – such as x, y, X, Y, Z, u', v', L*, a*, b* – are calculated for CIE 2° and 10° Standard Observers and CIE Standard Illuminants A, C, and D65.

Contact us for further information

Call the Instruments team on: 020 8943 6539
Email instruments@npl.co.uk

Last Updated: 10 Apr 2017
Created: 6 Aug 2009

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