National Physical Laboratory

Diffuse / Total Transmittance

Diffuse transmittance
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Total Transmittance

Measurements are made using a scanning spectrophotometer fitted with an integrating sphere accessory. The sample is placed in front of the sphere entrance port through which the light beam enters. The sphere collects all the light passing through the sample. Measurements can be made over the wavelength range 200 nm to 2500 nm at wavelength intervals from 0.5 nm to 100 nm. Bandwidths available for measurements are 0.5 to 5 nm from 200 nm to 860 nm and vary from 860 nm to 2500 nm. Uncertainties are typically of the order of ± 1%, but depend on the sample under test.

Diffuse Transmittance

Measurements are performed using the same equipment and over the same parameters as the Total Transmittances measurements, but with a hole in the light collector so that that light passing directly through the sample is not collected.

UV Transmittance Protection

UV transmittance protection
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Textiles can be measured to determine the protection they offer from the Ultra Violet (UV) radiation from sunlight. Measurements are made to appropriate British, European (BS EN 13758-1:2002), Australian and other international standards. These require the measurement of the total diffuse transmittance of textile samples at UV wavelengths from 280 nm to 400 nm at 5 nm intervals using a spectrophotometer fitted with an integrating sphere accessory. The integrating sphere enables collection of all the light that passes through the textile sample. The resulting spectral diffuse transmittance values are then used in conjunction with solar spectra data and biological activation data to calculate the required UV and solar protection factors.

Other diffuse transmittance properties can be measured, including measurement of angular transmittance and scatter through semi-transparent samples and also haze. Please contact NPL with your exact requirements.


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Last Updated: 22 May 2014
Created: 5 Aug 2009


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