National Physical Laboratory

Transmittance

Image courtesy of iStockphoto
Image courtesy of iStockphoto

Regular Transmittance

NPL is able to make regular transmittance measurements from 200 nm to 3000 nm. Spectral transmittance can be measured at either selected wavelengths or by using a scanning technique at regular intervals. Wavelength intervals are typically 5 nm and can be as low as 0.05 nm. Small wavelength interval scans are most useful when measuring wavelength standards that have narrow absorption bands. The spectral bandwidth used for wavelengths up to 800 nm is chosen by the customer and can be up to 5.0 nm. Above 800 nm the bandwidth usually varies with wavelength up to a maximum of 20.0 nm. NPL can measure samples mounted in 10 mm path length cuvette holders and can also measure smaller and larger and some irregular shaped samples. Typical measurement uncertainty for a 90% transmitting filter in the visible part of the spectrum is ± 0.2%. Uncertainties for other transmittance values are relative to the filter transmittance.

Solar Integrated Values

Solar integrated values of transmittance can be calculated using Parry Moon air mass 0, 1 and 2, or Makarova air mass 0 solar data.

Wavelength and Bandwidth (Transmissive Evaluation)

Where scans have been made on samples (at resolutions sometimes as low as 0.05 nm), such as bandpass filters, in addition to the determination of the wavelength of the transmittance / absorption peak, other data such as the half height bandwidth, centre wavelength, wavelength of centre of gravity of peak can be calculated.

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Customer Service tel: +44 20 8943 6151
E-mail: optical_enquiries@npl.co.uk

Last Updated: 22 May 2014
Created: 5 Aug 2009

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