Haze and Luminous Transmittance of Transparent Plastics
This standard test method covers the evaluation of specific light-transmitting and
wide angle light scattering properties of planar sections of materials like, but
not restricted to transparent plastic.
The test specimen shall be ø50mm (ø2”) in size, or an exact square piece of material,
completely clean and without defect (unless necessary). The test specimen could
also be just large enough to cover the testing unit entryway. Each specimen is put
through two procedures; 1) using a hazemeter and 2) using a spectrophotometer. Regular
luminous transmittance is obtained when placing a clear specimen at a distance from
the testing unit entryway. Hemispherical luminous transmittance is obtained when
placing a hazy specimen at the testing unit entryway.
During the hazemeter test a light beam is shone through a condenser, lens and then
the specimen into a spherical testing unit which gauges the amount of light/diffusion.
Test procedures using a Spectrophotometer differ slightly from that of the hazemeter
where the results are automatically computer calculated but give slightly lower,
more consistent results. If results from the Spectrophotometer are manually taken
then the results can be worked out in the same way as using the Hazemeter. Anything
with a haze value greater than 30% is considered diffusing. To calculate the results,
four readings are taken with parts of the testing units in several different positions
giving the user these units: T1, T2, T3 & T4, thus: